enlightenment in strata 3d cx

by Rodrigo Duarte

Enlightenmentin Strata 3D CX

Copyright 2005, WestRim Digital Arts.Unauthorized copying or distribution is prohibited. Do not post or share electronically without express written permission.

Unlocking the power of Strata Software

WestRim Digital Arts has been conduct-ing professional training classes on Strata products since 1999. The WestRim team of Instructors has decades of experience and knows Strata products inside and out. We provide the highest quality of instruction available to unlock the power of Strata for you and your business, school or organization.

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To see work done by Rodrigo Duarte using Strata 3D, please visit his profi le at Stratacafe.

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ContentsCo e sContentsContentsContentsContentsC t t

Lights in Strata 3D ....................................................19

Types of lights in Strata 3D .......................................19

General properties ....................................................20

Ambient Color.........................................................20

Intensity ..................................................................21

Color .......................................................................23

Applying color temperatures ................................23

Falloff ......................................................................24

Full Intensity Radius .............................................24

Total Falloff Distance ............................................24

Fall-Off ..................................................................25

Light Source Radius ...............................................26

Gels .......................................................................27

Colors and Images ...............................................28

Specular Refl ectance Scale .................................29

Diffuse Refl ectance Scale .....................................29

Volumetrics .............................................................30

Fog .......................................................................30

Mist .......................................................................31

FX ...........................................................................32

Hotspot .................................................................32

Lens Flare .............................................................33

Global lights ..............................................................35

Point lights ................................................................37

Spotlights .................................................................38

The Spotlight window .............................................38

Area lights .............................................................39

Lightdomes ...............................................................41

HDR v/s LDR ..........................................................41

ContentsLight: ....................................................1Let there... ..................................................................2

The nature of light .....................................................2

Wave or Particle, and why should I care? ................2

Wave .......................................................................2

Particle ....................................................................3

The middle ground .................................................3

How does that affect us? .......................................3

Properties of light .......................................................4

Intensity ....................................................................4

Falloff ........................................................................4

Shadows ...................................................................5

Interaction with objects ..............................................7

Refl ection..................................................................7

Specular refl ection ..................................................8

Diffuse refl ection .....................................................8

Diffuse interillumination ..........................................9

Transmission ...........................................................10

Absorption ............................................................12

Refraction ...............................................................12

Some common Refraction indices .........................13

Fresnel Effect ........................................................14

Caustics ..................................................................14

Transmission caustics ..........................................14

Refl ection caustics ...................................................15

Color temperature and light types ............................16

Color and Temperature .............................................17

Moving On ................................................................17

Lights in Strata 3D: ....................18


ContentsCo e sContentsContentsContentsContentsC t t

Creating HDR images .............................................42

Moving on... ..............................................................43

Exteriors: ....................................... 44The color of sunlight .................................................45

Default Strata 3D light ...........................................46

Adding a Skylight ...................................................47

Light Dome skylight ..............................................47

Clear day: Morning .................................................48

Clear day: Noon ......................................................49

Clear Day: Sunset ...................................................50

Clear Day: Dusk ......................................................52

Partly Cloudy ..........................................................52

Rendering considerations for soft shadows .........54

Hazy/foggy day ......................................................56

Sunny day, shady spot ...........................................58

Volumetrics and shadows ....................................59

Overcast .................................................................60

Clusters ................................................................60

Night time ...............................................................62

Interiors: ........................................63Lighting a simple interior ........................................64

The fi rst light .........................................................65

Lighting the scene more evenly ............................68

Textures and objects ............................................69

Adding lamps .........................................................70

The starting point..................................................71

Adding and adjusting a lamp ................................71

Adding a fl oor lamp ..............................................73

Modeling the lamp ................................................73

The main light .......................................................73

Simulating a bounced light ...................................74

Exterior light ...........................................................74

Creating the “window”..........................................74

Adding a “sun” .....................................................75

Adding a gel and moving the camera ...................76

Optional volumetrics .............................................76

Nighttime ..............................................................77

Raydiosity ...............................................................78

Collected light amplifi er ........................................79

Diffuse bounces ....................................................79

General tips ............................................................80

Beveling ................................................................80

Estimating light intensities using Photoshop ........81

Chapter ContentLet there... ..........................................2

The nature of light ............................2

Wave or Particle, and why should I care? ................................................2

Wave .................................................... 2

Particle ................................................. 3

The middle ground ............................... 3

How does that affect us? ..................... 3

Properties of light ...............................4

Intensity ............................................4

Falloff ...............................................4

Shadows ..........................................5

Interaction with objects ......................7

Refl ection .........................................7

Specular refl ection ............................... 8

Diffuse refl ection .................................. 8

Diffuse interillumination ........................ 9

Transmission ..................................10

Absorption .......................................... 12

Refraction .......................................12

Some common Refraction indices .13

Fresnel Effect ..................................... 14

Caustics .........................................14

Transmission caustics ........................ 14

Refl ection caustics ............................. 15

Color temperature and light types ...16

Color and Temperature ..................17

Moving On ........................................17

Light:HOW LIGHT BEHAVES IN THE REAL WORLD

Light interacts with matter in certain ways.We will begin by reviewing this behaviorprior to applying it to Strata 3D.


1 LightgLightLightLightLightLi ht

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Let there...This document is all about lighting, so a very good way to start would be an approach at what light is and how light behaves, the different ways in which it interacts with objects and which properties and interactions of light will be useful to us in our work in Strata 3D.

The nature of light

Light enables us to see things.

It is not by chance that light has been linked to manifestations of the divine from as far as we can reach into our past. The intangible nature of light and its power to make us aware of our surroundings is nothing short of magi-cal.

Light is an elusive phenomenon, and has been studied extensively, so we now have a pretty good idea about how it works, but not too good an idea about what it is.

One thing we are fairly certain of is that light is a form of energy, emitted from different objects for different causes, each of them with certain properties. Among these causes we can name:

FlamesHot objects (red-hot, white hot, etc.)Chemical reactionsFluorescenceBioluminescence (glowworms, fi refl ies, abyssal fi sh, etc.)LightningEtc.

There is a very wide range of possible light emitters; more than enough to keep us entertained exploring their representation in our digital art for a life-time, or more.

Wave or Particle, and why should I care?

From —at least— the time of the ancient Greeks, there has been an ongo-ing discussion about the nature —and behavior— of light. One of the most heated aspects of this discussion has been whether light behaves as a par-ticle (the particle of light is called a photon), or as a wave.

Wave

To those who think light behaves as an electromagnetic wave, light is some-thing similar to a radio wave, only with a higher vibration frequency that enables them to travel farther.

Wave-like behaviors of light include:

Refl ectionRefraction

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Interference (not used in Strata 3D)Correspondence between wavelengths and light color

Particle

Those who believe in the particle behavior of light think that light is com-posed of tiny billiard ball-like particles that interact with each other more or less as billiard balls do, colliding and bouncing off objects.

Particle-like behaviors of light include:

Refl ection (just like billiard balls)Traveling in a straight line

Different physicists have taken different stands on this discussion: Newton, for example, defended the particle view, while other physicists (or Natural Philosophers as they were called at the time) such as Young, spoused the opposite view. Both sides have had experimental and theoretical evidence to support their claims

The middle ground

In 1923, the French physicist Louis de Broglie found a middle ground that proved that photons and other particles have a dual nature: partly particle and partly wave. This may not be a once and for all solution to the problem but at least has appeased the discussion quite a bit.

It is now a consensus that all electromagnetic radiation (and even subatomic particles) has a dual nature. Sometimes it behaves as a particle, and some-times it behaves as a wave. The higher the energy of the entity, the more particle-like it will behave. The lower the energy, the more wave-like its be-havior

How does that affect us?

Strata 3D handles light in a simplifi ed way, using only those properties of light that are relevant to most 3D scenes.

Sometimes, some properties or phenomena are not handled directly by Strata 3D and we have to simulate them ourselves.

Most of the properties we are concerned with have to do with the way in which light interacts with objects and surfaces.

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Properties of lightSome properties of light are its own: properties such as intensity, color (and composition) have nothing to do with any interaction between light and oth-er objects but rather with how the light was produced.

Intensity

Light is energy.

A burning match does not hold a candle to a fl oodlight and even less to the nuclear reactions that cause the light of the stars.

The more energy that is released, the more intense the light is.

Falloff

The farther way we get from a light source, the less lighting we get from that light. Indeed, the intensity received from a light source decreases very rap-idly as we increase the distance to the light source.

The reason for falloff is that a certain amount of energy is produced and as it does away from the light source that same energy has to cover larger and larger surfaces.

The strength with which a light illuminates decreases rapidly as it moves away from the source

Let us suppose that 10 units of energy are emitted from a light source.

When the light is 10 inches away from the source the 10 units of light cover an area of 4π x 102 sq. inches (approx. 1200 sq. in.)

When the light is 20 inches away from the source, those same 10 units cover an area of 4π x 202 sq. inches (approx. 4800 sq. in.)

Light intensity decreases with the square of the distance.



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Lighting intensity obeys the inverse square law, so it decreases with the square of the distance between the light source and the object being lit.

Shadows

Where there is light, there is shadow, or should be.

A shadow is nothing more than an area where light does not fall because it was already refl ected by an object.

Shadows are seldom totally dark, because there are usually several light sources and bounces that light even dark areas. There is a kind of light called Ambient Light that has bounced many times and is non-directional. This kind of light is often responsible for the visible details in unlit areas.

Areas in shadow need not be totally dark

How hard or how soft the shadows are is determined by the size of the light source and by how far the source is.

A nearby light source casts softer shadows than a faraway light sourceA large light source casts softer shadows than a small light sourceA very distant source of light (such as the sun in a clear day) casts very hard shadows.A very large area light (such as the sky in an overcast day) casts small, very soft —at times indistinguishable— shadows.

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Light sources of increasing diameter cast increasingly softer shadows

Diffuse lighting produces very soft shadows.



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Interaction with objectsMost of the time what we see is light that has bounced off, or passed through, one or more objects. We usually do not see light coming straight from its source. Since most of our work in Strata 3D will have to do with the interaction between light and objects, it is profi table that we review these interactions briefl y.

The interactions that interest us here are:

Refl ectionSpecular refl ectionDiffuse refl ection

AbsorptionTransmission

RefractionFresnel EffectCaustics

To reproduce different objects, it is very useful to understand what is happening. Different refl ections, transmissions, refraction, etc., are combined in this depiction.

Refl ection

Light travels in a straight line.

Light bounces off most materials. This bouncing is called refl ection.

We can visualize this bouncing as something similar to what billiard balls do. The ray of light approaches the surface, hits it, and bounces off it.

There is a law in optics stating that the angle formed between the incom-ing ray of light and the normal (perpendicular) to the surface is equal to the angle formed between the normal and the outgoing ray of light. This law governs the refl ection in every surface but can produce quite different re-

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sults depending on the nature of the surface. Perfectly smooth (or nearly so) surfaces will refl ect light in an orderly fashion, while rough (on a very small scale) surfaces will scatter light in every direction.

Specular refl ection

When the surface on which the light strikes is smooth, the rays of light are refl ected in an orderly way. Every ray of light strikes a surface that has more or less the same normal and therefore bounces off more or less in the same direction of the other rays. This is called specular refl ection, from the Latin word speculum, meaning “mirror”.

In fact, a mirror is a perfect example of specular refl ection. All light bounces off the mirror in an orderly way, preserving the original image perfectly.

Light

Specular reflection

In specular refl ection, rays of light are refl ected in an orderly way

Diffuse refl ection

Diffuse refl ection occurs when light strikes a non-smooth surface. Because of the way light is refl ected, the direction in which each ray bounces de-pends on the normal for the particular point of the surface, and in this case, the normals point in different ways, and the rays of light are refl ected in dif-ferent directions. This is called diffuse refl ection.



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Light

Diffuse reflection

In diffuse refl ection, light gets refl ected in a scattered pattern

Most materials exhibit an intermediate behavior, refl ecting part of the re-ceived light specularly and part diffusely.

Surfaces such as mirrors refl ect most light specularly, but most metals, plastics, and other shiny surfaces exhibit both behaviors.Not all matt surfaces will be entirely devoid of specular refl ectivity. Notice for example the specular refl ections of the pavement on a sunny day.

Diffuse interillumination

Diffuse refl ection of light on an object can light other objects. This is not usu-ally apparent, but usually makes a big difference when aiming for realism. It is surprising to see how much diffuse materials light each other.

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Diffuse interillumination lights parts of scenes with diffuse light bounces.

Color bleed

Diffuse interillumination causes color bleed, Color bleeding occurs when light that bounces diffusely off a colored object lights other areas, imparting the color of the object.

Transmission

Light does not always bounce off objects. Sometimes light passes through objects. This is called transmission. It is also called transparency.

Several materials are transparent: air, several gases, glass, plastic, many liquids, gems, etc. Several other materials are partly transparent (partial transparency is called translucency). A totally transparent object is invisible. Most transparent objects are not fully transparent, but partly transparent and partly refl ective (most commonly exhibiting specular refl ection).



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A fully transparent object is invisible

For transparent objects to be seen refl ection is required, often specular refl ection

Real-world materials, such as plastics, glass, quartz, etc., are not fully trans-parent. They transmit part of the light they receive and refl ect back the rest.

In the case of colored materials, for example cobalt glass, most colors are being transmitted by the glass, but blue is being refl ected. Several other ma-terials exhibit this same behavior and are responsible for a series of colors glass, plastics, etc. In most of these cases, the color is caused by absorp-tion of certain parts of the spectrum by the material.

This behavior does not only happen in transparent materials.



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Absorption

As in the cobalt glass example, sometimes not all colors are transmitted or refl ected equally.

In many cases, some colors are transmitted and some are refl ected, and for some materials, some colors are absorbed (more strictly speaking, light of a certain wavelength is absorbed). What we see in those cases is the refl ected light, that has all the colors of the light that was falling on the object minus the color that was absorbed. Supposing we originally had white light (light composed of all visible wavelengths) what we get is the complementary color of the color that was absorbed.

If the absorbed color is red, we see cyanIf the absorbed color is yellow, we see blueIf the absorbed color is green, we see magentaIf the absorbed color is cyan, we see redIf the absorbed color is blue, we see yellowIf the absorbed color is magenta, we see green.

In the cobalt glass example, what happens is that the substance is absorb-ing the yellow component of light and the refl ected and the transmitted light are now blue.

Refraction

When light passes from one medium (usually air) to another, the rays of light change speed (usually slow down) and direction. This causes the typical “breaking” of objects seen partly in water and partly in the air.

This deviation of the rays of light is called refraction.

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The Refraction index of a substance is a value that measures the deviation of a ray of light passing from vacuum (Refraction index=1.0000000000) to the substance.

Refraction causes the apparent breaking of an object seen partly in air and partly in water

Each substance has it own refraction index. The refraction index of a sub-stance is so particular to it that it is used in chemical analysis to determine the degree of purity.

Refraction is also seen in other phenomenon called caustics, which is partly caused by light being concentrated by refraction.

1.0 (vacuum)

1.33 (water) 1.5 (glass)

2.4 (diamond)

Different materials have different refraction indices

Some common Refraction indices

General

Vacuum: .......................... 1.0Air: ................................... 1.0003Ice: .................................. 1.31Water:.............................. 1.33Plexiglass: ....................... 1.48Pyrex Glass: .................... 1.46Glass: .............................. 1.5-1.6Lead Glass: ..................... 1.6-1.8

Liquids

Beer: ............................... 1.34Ethyl Alcohol: .................. 1.36Quartz: ............................ 1.46Vegetable Oil: .................. 1.47

Gems

Opal: ............................... 1.45Moonstone: ..................... 1.52Amber: ............................ 1.54Agate:.............................. 1.55Emerald: .......................... 1.58Jade: ............................... 1.6Topaz: ............................. 1.62Ruby:............................... 1.77Sapphire:......................... 1.77Zircon: ............................. 1.85Cubic Zirconia: ................ 2.05Diamond: ........................ 2.42

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Some common Refraction indices

General

Vacuum: .......................... 1.0Air: ................................... 1.0003Ice: .................................. 1.31Water:.............................. 1.33Plexiglass: ....................... 1.48Pyrex Glass: .................... 1.46Glass: .............................. 1.5-1.6Lead Glass: ..................... 1.6-1.8

Liquids

Beer: ............................... 1.34Ethyl Alcohol: .................. 1.36Quartz: ............................ 1.46Vegetable Oil: .................. 1.47

Gems

Opal: ............................... 1.45Moonstone: ..................... 1.52Amber: ............................ 1.54Agate:.............................. 1.55Emerald: .......................... 1.58Jade: ............................... 1.6Topaz: ............................. 1.62Ruby:............................... 1.77Sapphire:......................... 1.77Zircon: ............................. 1.85Cubic Zirconia: ................ 2.05Diamond: ........................ 2.42

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This change of direction is known as refraction, and is a property of each material.

Fresnel Effect

Ever seen a mirage, or wondered why, if water is transparent, we cannot see any transparency, but rather mirror-like behavior when staring into the horizon?

Fresnel effect causes mirages

The answer is called Fresnel Effect. This is simply that the amount of refl ec-tance of a surface varies with the viewing angle.

When the surface is being viewed at 90 degrees, the refl ectance is minimal and the transmission is maximized. As the viewing angle is reduced, the refl ectance of a surface increases and the transmission decreases. When the viewing angle becomes smaller than the critical angle (depends on the Refraction index of the substance) all light is refl ected and nothing is trans-mitted.

Caustics

If you ever burned paper using a magnifying glass and sunlight when you were a kid, then you know what caustics are. Caustics are the concentration of light caused by refl ection or refraction.

Transmission caustics

Transmission caustics are a concentration of light passing through a trans-parent object and concentrated by refraction. This wold be the typical ex-ample of using a magnifying glass to burn paper.



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Refl ection caustics

Refl ection caustics are caused by the concentration of refl ected light. A typi-cal example would be the pattern that appears when a ring is laid fl at on a horizontal surface.

Refl ection caustics are caused by the concentration ofrefl ected light



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Color temperature and light typesThere are several possible kinds of light sources, from an open fi re to a fl uorescent tube to a fi refl y, and the different light source kinds will provide different types of light.

For example, a fl uorescent tube will light a scene differently than a candle will.

The same scene will be lighted differently by two different light sources

Color temperature is measured in degrees Kelvin1. This is because how these temperatures were fi rst measured.

1 One degree Kelvin equals one degree Celsius. Degrees Kelvin are based on the absolute zero (the coldest temperature that can be reached) which is reached at -273 Celsius.



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Color temperature was originally determined by heating a carbon block and correlating the temperature with the color of the emitted light. As you heat this carbon block (also called a black body), the color will go from red-hot to white-hot to bluish.

This correlation between temperature and color holds true only for incan-descent light sources, such as light bulbs, fl ames, etc., but nevertheless is used for all light sources.

Color and Temperature

The following table correlates the color temperature of different light sources with the color associated to it.

Color Color Temperature (K)

Light Source

1200 Candle

2800 Tungsten Lamp(common light bulb)

2800 Sunrise

2800 Sunset

5000 Average Daylight

6000 Bright Midday Sun

8000 Hazy Sky

10000 Overcast Sky

Moving OnNow we have a common ground for understanding how light works.

In the next chapter we’ll explore how Strata 3D deals with light.

Lights in Strata 3D:HOW STRATA 3D HANDLES LIGHT

Strata 3D handles light in a simplifi ed way to avoid getting caught in cal-culations forever. This chaper explains how Strata 3D does it.

Chapter ContentLights in Strata 3D ............................19

Types of lights in Strata 3D ..............19

General properties ............................20

Ambient Color ................................20

Intensity ..........................................21

Color ..............................................23

Applying color temperatures .............. 23

Falloff .............................................24

Full Intensity Radius ........................... 24

Total Falloff Distance .......................... 24

Fall-Off ................................................ 25

Light Source Radius .......................26

Gels ...............................................27

Colors and Images ............................. 28

Specular Refl ectance Scale ............... 29

Diffuse Refl ectance Scale .................. 29

Volumetrics ....................................30

Fog ..................................................... 30

Mist .................................................... 31

FX ...................................................32

Hotspot .............................................. 32

Lens Flare ........................................... 33

Global lights .....................................35

Point lights .......................................37

Spotlights .........................................38

The Spotlight window ....................38

Area lights .......................................... 39

Lightdomes ......................................41

HDR v/s LDR ..................................41

Creating HDR images ....................42

Moving on... .....................................43


2 Lights in Strata 3Dg s S a a 3Lights in Strata 3DLights in Strata 3DLights in Strata 3DLights in Strata 3DLi ht i St t 3D

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Lights in Strata 3DAfter the overview about how light behaves, we will now have a look at how lights work in Strata 3D, seeing how the general behavior of light applies to the program, and what behaviors of light are taken into account in Strata 3D and which ones are not.

Types of lights in Strata 3DBefore going into the general properties of Strata 3D lights, it is a good thing to know what kinds of lights are available to us in the program. These are:

Global lightsInfi nitely distant lights (parallel rays) that can only cast hard shadows. Limited FX can be applied to them. Should be used as sunlight only.Point lightsLights that behave more or less as light bulbs. They are good for (but not limited to) lighting interior scenes.Spot lightsThese lights can be aimed at objects and have adjustable beams. They are much used because they provide the greatest amount of control of all lights.Light DomesLight domes provide global illumination (not to be confused with global lights). This type of light requires the Raydiosity renderer to be of use. Any background (and only a background) can be used as a light dome. HDR images are frequently used for lightdomes.Area lightsThese are also Raydiosity-only lights. They are created by applying a texture with a glow value greater than zero to any object, which then acts as a light-casting object.

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General propertiesThere are properties common to (almost) all light types in Strata 3D. We will discuss them here before going into each specifi c light type.

Area lights and light domes are different beasts, so some of the properties that will be discussed here do not apply to them.

Ambient Color

The ambient color is not exactly a property of any light in Strata 3D, but is a very important element to take into account while lighting.

Ambient light is light that has bounced so many times that we no longer know where it is coming from. Strata 3D simulates this phenomenon by us-ing a base color, called the Ambient color, to avoid having unlighted areas being black.

Ambient color set to 90% black and to 50% black

Aside from defi ning the intensity of the ambient light, the ambient color also defi nes the color of the ambient light, and can be used to set moods or environments. For example, an underwater scene will benefi t greatly from a blue Ambient color.

Ambient color set to dark red and dark green

For those of you who are into space scenes, it is important to keep in mind that in outer space there is no ambient, because it is mostly empty space, so there are rally few places for light to bounce off and become this “back-ground light.“



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Space scenes should not have any ambient light

When working on a space scene then, keep in mind that either unchecking the Enable check box under ambient or setting the ambient color to black will result in no ambient light preset in your scene.

Intensity

The intensity of most Strata 3D lights is controlled by a slider that goes from 0% to 100%, but larger values can be typed by hand to obtain an intensity greater than 100%.

Scene lighted with a 25% and a 50% intensity spotlight, plus a fi ll light




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Also, negative intensity values can be typed into the intensity fi eld, so the lights can also be used to “suck light off” a scene.

When using a negative intensity light, the specular highlights will be dark and the shadows may be light.

A -100% intensity spotlight is used here to create a dark zone on the image.

A negative intensity spotlight and white ambient color can be used to create a negative image (in case using Photoshop is out of the question).

A -100% intensity spotlight plus white ambient color create a negative image



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Color

We can control the color of our global lights, spotlights and point lights by clicking in the color miniature of the appropriate palette.

Color selector for a global light and for a Spotlight.

The color selector for point lights is very similar to the one for a Spotlight

In the case of light domes, the color will be already present in the back-ground, be it a color, horizon or image-based.

In the case of area lights, the glowing texture needs to be colored to impart a color to the light.

It is important to keep in mind that the choice of darker colors will decrease the intensity of the light. As shown by the images below, at the same light intensity, if the light color darkens, the light appears to lose intensity.

Scene lighted with a 75% intensity spotlight with darkening gray colors.

Applying color temperatures

One place to assign the light’s color based on the color temperature of a particular light source can be the light color. However, if we plan to build a library of light sources and their colors (a wise move), a better idea would be to build a library of gels to have faster access to the different light types.



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Falloff

We already saw that the light emitted by a source loses intensity the farther the illuminated object is from the source.

Point lights and Spot lights have Falloff.Global lights do NOT have Falloff. This is because the light source is supposed to be (almost) infi nitely distant and no signifi cant falloff can be perceived in the small scale the scene’s dimensions are compared to the distance of the light.

We can control the falloff of lights in Strata both numerically and interac-tively.

Full Intensity Radius

This value controls at which distance does the falloff begin for a light.

In real world lights, the falloff begins immediately after leaving the surface of the light source. In Strata 3D we can control where does the falloff begin either numerically or by:

Dragging the inner ring (point light)Dragging the red square closest to the light (spotlight)

Total Falloff Distance

The total Falloff Distance defi nes the full reach of the light before losing power entirely.

To control the falloff of a point or spot light we can either enter the total falloff distance value in the Object palette, object tab or do it interactively:

Dragging the outer ring (point light)Dragging the red square farthest from the light (spotlight)

Full intensity Distance


Full intensity and Total Falloff Distance rings for a point light

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Full intensity Distance


Full intensity and Total Falloff Distance rings for a spotlight

Fall-Off

Strata 3D can calculate the falloff for a light in two different ways: Linear and exponential.

Exponential is the way in which the intensity of light decreases in the real world

Linear is not accurate, but can be of use in cases that the light intensity lowers too fast for our needs as a good alternative to increasing the Full Intensity distance to uncomfortable distances.

Two renderings of the same scene. The image on the left has a point light with ex-ponential falloff. The image on the right has the same point light set to linear falloff.

The total falloff distance increases from 100 in. to 720000 in. when changing from exponential to linear.



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Light Source Radius

When our fi nal image or animation needs soft shadows, the light source radius becomes important, because the softness of the shadow will depend on the light source radius.

Light source radius set to 0.1 in, 1 in, 5 in, and 10 in.

There is no need to concern ourselves with this value if we are using straight Raytracing with no soft shadows.

5 in. light radius rendered in Raytracing best (left) and Soft Shadows (right)

It is important to remember that the light source radius is not the only vari-able in determining the shadow softness. The distance at which the light source is set from the object is also of importance.



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Closer to the light:harder shadows

Farther from the light:softer shadows

When objects are close to the light source, their shadows are comparatively hard. As the objects move away from the light source, their shadows be-come softer.

Gels

Gels are essentially textures for lights. We can use them to add ambience to our scenes, to color the lights so they resemble a certain kind of light ac-curately and to control the specular highlights and diffuse lighting a certain light provides.

A Light gel can easily turn plain lighting into something with more ambience and texture

Just like textures, we can layer gels on top of each other. Unlike textures, though, we cannot control blend modes. Keep in mind that a black pixel in a gel map will remain dark no matter what other gels we layer on top of it.



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Gels can be layered on top of each other

Colors and Images

Just like image textures, we can control color, image map, repetitions and scaling in light gels.

NameThe name of the gel. It is always a very good idea to assign meaningful names to things, specially in complex projects.Copy fromWe can create new gels based on existing ones. This menu allows us to select the gel we will use as a starting point for our new gel.ColorWe can assign a color to our gel. Clicking here will open the system color picker.MapWe can use image maps for our gels. Clicking here enables us to load and do minor adjustments to the map we use for our gel.TilingJust like with Image textures, we can set the tiling of the map we are using. We can choose from:

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NormalRepeats the map normally MirroredRepeats the map, mirroring it each time there is a repetitionNoneThe map is applied only once

x scaleControls the horizontal scale of the mapy scaleControls the vertical scale of the mapSpecular Refl ectance ScaleControls the size of the specular highlights (see below)Diffuse Refl ectance ScaleControls the intensity of the diffuse refl ections (see below)

Specular Refl ectance Scale

We can adjust the size of the specular highlights by altering the Specular refl ectance scale .

A Specular refl ectance scale of zero means there are no specular high-lights at all.The default value for the Specular refl ectance scale is 1Values larger than 1 will result in larger than normal specular highlights.

Specular refl ectance scales of zero, 1.0, 2.0 and 10

Diffuse Refl ectance Scale

The Diffuse Refl ectance Scale value controls the intensity of the diffuse re-fl ection for the light.

A Diffuse Refl ectance Scale of zero results in no diffuse refl ection

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The default value for the Diffuse Refl ectance Scale is 1.A Diffuse Refl ectance Scale with a value greater than 1 will result in increased diffuse refl ection (see image below).

An interesting application of Diffuse refl ectance scale is turning it to zero to help obtain a specular-only pass to compose passes separately later on.

Diffuse refl ectance scales of zero, 1.0, 2.0 and 10

Volumetrics

Volumetrics are a group of shaders that are applied to several objects (3d shapes, environment, lights) that fi ll the volumes.

Lights accept two of these volumetric shaders: Fog and Mist.

Besides applying the shaders directly to the lights, we can also apply them to the air of the scene. In either case, lights will cast volumetric shadows if the check box is applied.

Fog

Fog is a semitransparent volumetric shader that does not evolve over time (even though its parameters can be animated). It can cast shadows and has multiple confi gurable parameters such as color, density, falloff, etc.

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A Fog shader applied to the spotlight

A similar Fog shader applied to the air. Some density adjustment was required

Mist

Fog is a semitransparent volumetric shader that can evolve over time. It has a cloud like texture and can cast shadows.



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Mist shader applied to the street lights

FX

FX, or special Effects are mostly post-rendering effects that are applied to different objects of a scene. Lights support two FX: Hotspot and Lens Flare.

Hotspot

A hotspot is a glowing spot with rays of light. We can confi gure the color, intensity, ray number, saturation, etc. for the Hotspot.

The Hotspot parameters can be animated.



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Lens Flare

A lens fl are is basically a Hotspot with glare. It mimics the fl ares we some-times get because of internal refl ections and refractions in camera lenses.

The Lens Flare parameters can be animated.



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A somewhat exaggerated lens fl are applied to one of the point lights in the building



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Global lightsNow that we have already covered the common properties for Strata 3D lights, we can focus on the lights themselves. We will start with global lights.

As we have already mentioned, global lights simulate sunlight. They have the following properties:

Parallel raysNo falloffDo not accept volumetric shadersHard shadows onlyThey do not produce caustics

Global lights are created and managed in the Lights tab of the Environment palette (E key).

Exterior scene lit only with global lights

It is not advised to use many global lights. In this book, we’ll never use more than two. All additional lighting should be handled by point lights or spot-lights.

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Global light set to front and back. We can toggle the side by holding the Command (or Control in Windows) key while dragging the light

The circle in which the global lights are set has the ambient color, so we can see at a glance what is the ambient color we are using.

The circle in which the global lights appear represents a sphere. Notice how, when moving the light, it gets distorted when approaching the edges of the circle. If such is the case, it is a good idea to change view in our scene to be able to manipulate the light with ease.

When using a ground plane beware of setting the global light under the hori-zon line. This happens quite often, specially if we are manipulating the lights in an isometric view.

Often, the light appears “on the other side of the sphere”, and lights our scene from the back. If we do not want that, we can Command (Ctrl in Win-dows) drag the light. That will bring it back to the “front” side of the sphere.



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Point lightsPoint lights are light bulbs. They light the scene in all directions. A summary of their properties follows:

Rays radiating from a point in all directionsLinear or logarithmic falloffAccept volumetric shadersHard or soft shadowsCan produce caustics

A typical application of point lights is lighting interior scenes. Just like in actual interior scenes, many point lights may be required to light a scene appropriately.

The falloff for point lights can be controlled by dragging the inner ring (full intensity radius) and the outer ring (total falloff distance).

If there rings are close, the point light will have a small penumbra — an abrupt transition between lighted and dark areas.

If the rings are far apart, there will be a smooth transition between lighted and dark areas.

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SpotlightsSpotlights are the most versatile lights in Strata 3D. Their properties can be summarized as follows:

Rays radiating from a point in a cone. We can set the angle of the cone.They always have falloff. It can be either linear or logarithmic falloffAccept volumetric shadersHard or soft shadowsCan produce caustics

The Spotlight window

We can double-click a spotlight to open the Spotlight window. This window shows us what the spotlight “sees”, and allows us to control the position of the spotlight in the same way we control the position of a camera.

We can also control the angle of the cone of light projected by the spotlight using the horizontal slider on top of the window. The cone angle corre-sponds to the inner ring of the Spotlight.

Double-click hereTo open this window

Softness

The softness of the ray of light emitted by the spotlight can be controlled either manually by dragging the outer ring of the spotlight or by the softness slider in the Objects palette, Object tab.

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Hard and softer spotlight beam edges

Area lights

Area lights are Raydiosity-only, because they use a texture’s Glow value as a source of light, and Raytracing cannot do that.

Raytraced v/s Raydiosity rendered scene with no lights and an object with a

glowing texture

When using area lights for lighting, the glow value of the texture used for the light source determines the intensity of the light the object will emit.



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Glowing object with a texture that has glow values of 1.0, 2.0, 5.0 and 10.0



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LightdomesFrom version 4.0 (aka CX) Strata 3D enables us to light our scenes using Light domes.

A Light dome is a Strata background that casts light. Any Strata 3D back-ground can be used as a Light Dome.

A Solid color background, Horizon, Spherical and Spherical HDRI used as Light

domes

Light Domes are mostly Raydiosity only. Although we can obtain light from a Light Dome in Raytracing, images come out fl at, with little suggestion of volume and no shadows. To make the most of a Light Dome, we need to use Raydiosity rendering.

Scene lit by a Light dome rendered in Raytracing (left) and Raydiosity (right)

HDR v/s LDR

Light Domes are best suited for using images as backgrounds. Both spheri-cal or cubic backgrounds will work quite well.



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Basically there are two types of images we can use as backgrounds: LDR and HDR images. LDR (Low Dynamic Range) images are regular 8 bit per channel per pixel images, the sort we use in our everyday work. HDR (High Dynamic Range) images are images with more information per channel per pixel, that store luminance values. These values can be understood by Stra-ta 3D and converted back into a light source.

Scene lit by a light dome using a LDR image (left) and HDR image (right)

There are two supported HDRI (High Dynamic Range Image) formats sup-ported by Strata 3D: OpenEXR (.exr) and Radiance (.hdr).

Creating HDR images

HDR images can be created in Photoshop CS2 by merging different shots of the same scene taken at different f-stops and then using the merge to HDR command (File>Automate>Merge to HDR...).

First, the images from which the HDR image will be created are selected.

Then, the exposure settings are entered for each one of the images used.

After that, the white point preview is manually adjusted, and the image is calculated. In the Photoshop help there is more abundant information con-cerning creating your own HDR images.



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Moving on...We now have a grasp of what kinds of lights are supported in Strata 3D and what do they do.

We will now put this knowledge to use, exploring and discussing some typi-cal lighting setups for exteriors, interiors and studio settings.

Chapter ContentThe color of sunlight .........................45

Default Strata 3D light ...................46

Adding a Skylight ...........................47

Light Dome skylight ........................... 47

Clear day: Morning .........................48

Clear day: Noon .............................49

Clear Day: Sunset ..........................50

Clear Day: Dusk .............................52

Partly Cloudy ..................................52

Rendering considerations for soft shad-ows ..................................................... 54

Hazy/foggy day ..............................56

Sunny day, shady spot ...................58

Volumetrics and shadows .................. 59

Overcast .........................................60

Clusters .............................................. 60

Night time .......................................62

Exteriors:LIGHTING EXTERIOR SCENES

Time to apply what we have reviewedWe’ll start by lighting exterior scenes at different times of the dayand conditions


3 Lighting exterior scenesg g e e o sce esLighting exterior scenesLighting exterior scenesLighting exterior scenesLighting exterior scenesLi hti t i

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Let us begin lighting things.

Let us start outdoors.

In most cases, our exterior scenes will be lighted by the sun, either directly or diffused through clouds, foliage or other obstacles.

Before reviewing the different lighting techniques, it will be profi table to have a look at how sunlight behaves at different times of the day and in different weather conditions.

The color of sunlightThe color and light intensity of the morning sun is different from the noon sun and different from the sunset. This is due to different reasons, but the main variable involved is how much air does sunlight have to go through. In air, blue light is scattered 6 times more than other colors, so at sunrise and sunset, when sunlight passes through more air than at noon, because of the angle at which it falls, more blue light is scattered, and yellow is the complementary color for blue.

Noon

Sunrise Sunset

The color temperature of the sun changes during the day

Sunrise/SunsetSunlight goes through more air

and gets scattered more

NoonSunlight goes through less air

so there is less scattering

Air scatters blue light more than other colors. The more air sunlight goes through, the more blue light gets scattered and the yellower the light looks.



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That is the very same reason why the sky is blue. With all the scattered blue light (over other colors) the sky is full of blue light bouncing around, and that light imparts its blue color to the sky.

In some cases like just before a storm, in contaminated cities or during vol-canic eruptions, sunsets can be orange to red. This is also due to the scat-tering of blue, violet and other shorter wavelength light by the dust, water and other particles in the air. What we see is the remaining, non-scattered light, corresponding to longer wavelengths (red, orange, yellow).

Default Strata 3D light

Now that we are ready to begin lighting our exterior scene, let us have a look at the default lighting we get in Strata 3D.

The default light Strata 3D has when creating a new scene is a 95% intensity global light and a 95% black Ambient color. These add to 100% intensity.

The image above shows a scene rendered using the default light. It has the problem that areas that are not lit by the global light are fl at. There is no de-tail to be seen, and that is not how light works, nor how we’d like our images to look.

This scene with the default light can be found in the CD. The fi lename is ex-terior_default.s3d and is in the 3.- Exteriors folder. From there you can follow the different lighting conditions that will be discussed here.



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Adding a Skylight

In exterior scenes, there is an ambient light caused by all the scattered blue light of sunlight, that helps light the scene, causing the detail in areas that aren’t lit by the sun to be visible. One way to simulate this skylight is using another global light, 40% in intensity, with a light blue color.

30% skylight, 85% sun, plus a refl ected environment

The image above shows a 30% skylight and a 85% “sun”. Aside from the skylight, a simple horizon refl ected environment was added to the scene to give it more coherence.

The skylight has the following properties:

Color: light blueIntensity: 30%Cast shadows check box unchecked.A gel that has a specular refl ectance of 0 to avoid specular highlights for the skylight (there is one in the Goodies folder).

This gel eliminates specular highlights from the skylight

Light Dome skylight

Another way to simulate the skylight is using the same refl ected environ-ment as a lightdome. The example below shows the same scene using the Horizon environment as a lightdome set to an intensity of 30%.

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A horizon lightdome can hide detail in the shadow areas

This technique has the drawback that the Light dome hides the detail in the shadow areas. The image above shows that the details of the tile are lost in the hydrant shadow. This happens both when using Raytracing and Raydiosity.

Clear day: Morning

Morning light is yellow colored, because the angle at which it enters the atmosphere makes it travel through a lot of air, and the blue light scatters, leaving it complementary color: yellow.

Because of the low angle, shadows are long.

To create morning light for a scene we need two global lights:

Sunlight: A light yellow light that casts shadows, set to an intensity of around 85% and falling at an angle on the scene.Skylight: A light blue light that casts no shadows, set to an intensity of around 30%

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For this example we will also use a Horizon refl ected environment set to light blue on top and bottom, and white on the horizon.

Of course, any suitable refl ected environment can be used. Of the default backgrounds that come with Strata 3D, Apple orchard, Residential streetand Mountains are good for daylight exterior scenes.

The image below is rendered using the RT Best render preset.

Morning sun is yellow in color and casts long shadows

Clear day: Noon

Around noon the light adopts a bluish cast. This is because the skylight is strong and sunlight is not yellow. At noon, sunlight passes through a thin layer of air and, as less blue light is scattered, the color of sunlight is not yel-low, but white. The bluish cast is actually imparted by the skylight.

To create noon light for a scene we need two global lights:

Sunlight: A white or very light blue light that casts shadows, set to an intensity of around 85% and falling almost vertical on the scene.

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Skylight: A light blue light that casts no shadows, set to an intensity of around 30%

For this example we will also use a Horizon refl ected environment set to light blue on top and bottom, and white on the horizon.



Noon light is bluish in color and casts very short shadows

Shadows around noon are very short, because of the position of the sun. Noon shadows are also dark, because the sun is at its maximum intensity.

Clear Day: Sunset

As the day progresses, shadows begin lengthening again, and as sunlight passes through an increasingly thicker layer of air, the light becomes in-creasingly yellow, with an orange tinge.

To create sunset light for a scene we need two global lights:

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Sunlight: A yellow/orange light that casts shadows, set to an intensity of around 85% and falling at an angle on the scene to cast long shad-ows.Skylight: A light blue light (slightly darker than the skylights on the pre-vious examples) that casts no shadows, set to an intensity of around 30%

For this example we will also use a Horizon refl ected environment set to blue on top and bottom, and light orange on the horizon.



Long shadows and yellow-orange light are typical of sunsets

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Clear Day: Dusk

At dusk the sun has gone and only a little skylight remains.

Even though it is not the most canonical solution, I fi nd that two global lights set ton the following parameters work pretty well:

25% intensityLight blue colorNo speculars gelNo shadows.

Essentially, both these lights are fi ll lights. The idea is to have detail be vis-ible.

Partly Cloudy

Partly cloudy days require a change of lights.

Global lights are unable to cast soft shadows, and we need soft shadows for anything other than a perfectly clear day

A good way to create a gel is the following:

Create a new Photoshop image, 512x512 pixels in sizeSelect the default colors (D key). This will leave black as the foreground color and white as the background color.Apply the Render>Clouds fi lter. Because of the image size (a power of 2), there is no need to apply the Offset fi lter and rubberstamping. The image is spontaneously non-tiling1

1 Tip learned at Red Rock Revival 2004 from an attendee.

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Adjust levels/curves until a good balance between grays and whites is achieved. Avoid excessive contrast.Create a new light gel in Strata 3DCopy the image and paste as the image for the new gel

If you want to, reduce the specular refl ectance scale to 0.7, to reduce the specular highlights a bit.

Of course, you can also load the gel that is in the CD (Goodies folder), that was created in the same way.

This gel is applied to a very distant spotlight. Have a care to increase the total falloff distance, and if needed the full intensity radius to have a good light intensity in the part of the scene we are rendering. Also, the beam width rings may need adjustment, as we are trying to trick the spotlight into behav-ing like a global light.

For the sake of comfort, once the spotlight is properly positioned, it can be turned into a Shy object by pressing Cmd (or Ctrl in Windows)+5. Shy ob-jects are objects that do not appear in the modelling window but do appear in the rendered image.

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A very distant spotlight is used as a “sun” in a partly cloudy scene

It is probably a good idea to convert the spotlight into a Shy object (Cmd (Ctrl)+5) to avoid uncomfortable overuse of the magnifying glass tool.

Rendering considerations for soft shadows

In order to get the soft shadows caused by the diffusion of light by clouds or other particles present in the air, soft shadows must be enabled.

The easiest way to activate soft shadows is using the Soft Shadow presets available in the toolbar. However, these may be a little slow and too detailed for our purposes.

In the Render window, expert button the amount of Light/Shadow samples can be changed (It is assumed we are using the Local Lights Good Soft Shadow preset).



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The light/shadow samples control the quality of soft shadows

Of course, there is a trade-off between speed and shadow quality. Trial and error will defi ne the best settings for each case. In the examples here 32 light/shadow samples were used for the sake of speed.

The Randomize light samples check box helps diffuse the shadows in case the samples are too few and banding appears in the shadows.

Depending on how cloudy we want our day to appear, the gel can be made darker or lighter, and the specular refl ectance scale can be adjusted accord-ingly.

This is a very lightly cloudy day

As the day gets cloudier, the light raises its color temperature, going from yellowish to white and even a cold white, and the light is more diffused by the clouds, so aside from modifying our light gel, the light source radius and color of the spotlight we are using should also be modifi ed.



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A cloudier day

An even cloudier day

If the day is defi nitely an overcast day, other lighting ways are better than a single soft spotlight. A light dome or point light clusters are better solutions in this case.

Hazy/foggy day

On a hazy day (or for those of us who live in cities prone to smog, on a nor-mal day) the air is not clear, with a haze or smog present.



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For this kind of day we need a spotlight, because the light is diffused by the fog or haze and casts soft shadows, and global lights do not support soft shadows.

A Fog shader applied to the spotlight is a good solution for hazy days

For this example, there is a very far away spotlight with a yellowish fog ap-plied.

The fog shader (shown at left) is the default shader set to yellow, colors linked and shadows enabled.

When shadows are enabled the rendering time increases, but depending on the scene composition, interesting applications of the Tyndall effect can be made.

Fog applied to the spotlight



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Sunny day, shady spot

We may set our scene on a perfectly clear day, but need a shady spot. Of course modelling a complete tree is justifi ed only if it will appear in the scene. Many times we only need the appearance of an off-scene tree to fi lter the light.

This can be easily accomplished by using a fi lled square with a stencilled texture put between the light source and the camera view.

There is a wide variety of useful images for this purpose: often some play-ing with painting parts of an image in Photoshop, adding noise, blurring and posterizing or applying Threshold will yield satisfactory results.

Image used as stencil for projecting a “tree shadow”

Depending on our needs, using soft shadows may be a good idea. Often the use of few samples can create interesting patterns. This is defi nitely a matter of experimentation.



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A fake shadow is projected into our camera view

Volumetrics and shadows

The use of stencilled panels is useful only if we do not need volumetrics such as fog and mist in our light sources. If this is the case, we need actual geometry to create crepuscular rays.

We need actual geometry for this kind of effect

An easy way to create geometry from the same map we had previously been applying as a stencil is to simply copy from Photoshop and paste into our Strata 3D scene. The pixels will be converted into geometry.

This way of working creates somewhat larger scenes, but enables us to make the most out of volumetric shaders used together with lights.



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Overcast

In an overcast day light comes from everywhere because sunlight has been totally diffused by the clouds. This is best created by a lightdome and ren-dered using Raydiosity.

In the example, a simple background is used: a Horizon in grays and whites, both as light dome and as refl ected background.

In overcast days there are little or no specular highlights

When using a lightdome there are no specular highlights. This may be a problem in other circumstances, but in this case it is a very good thing.

The screenshot at the left shows the horizon background used as a light-dome. Global lights are visible, but they are not in use: both are set to Con-struction lights.

Clusters

If there is no time to do a Raydiosity render, using a cluster of point lights is a viable solution. A cluster is a group of lights. In this case, we will replicate instances of a shape that contains a point light.

Create a new shapeInsert a point lightPut a cube around itMake the cube a construction object (this will enable us to drag the lights around easily)Set the point light to a very light blue color and lower its intensity to 10% Drag an instance of the shape we just made into the scene. Replicate the instance until there are 24 instances of the shape in the scene.

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With all these low intensity lights in our scene we can do a Raytracing ren-dering that will be much quicker than a Raydiosity rendering and will obtain satisfactory results.

An overcast day made with a light cluster



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Night time

A basic night time lighting setup is simply a blue skylight without any shad-ows and a low intensity. I fi nd that 30% works well.

A good refl ected environment for a night scene is a Horizon background going from dark blue to light blue and back.

In most night time scenes we will have other light sources aside from the skylight. For that we will have to use lamps and other light sources.

Depending on the night scene, the lights will be different. The example im-age uses six spotlights of 45% intensity and a bluish white color.

Chapter ContentLighting a simple interior ................64

The fi rst light ....................................... 65

Lighting the scene more evenly ......... 68

Textures and objects .......................... 69

Adding lamps .................................70

The starting point ............................... 71

Adding and adjusting a lamp ............. 71

Adding a fl oor lamp ............................ 73

Modeling the lamp ............................. 73

The main light ..................................... 73

Simulating a bounced light................. 74

Exterior light ...................................74

Creating the “window” ....................... 74

Adding a “sun” ................................... 75

Adding a gel and moving the camera 76

Optional volumetrics .......................... 76

Nighttime ............................................ 77

Raydiosity.......................................78

Collected light amplifi er...................... 79

Diffuse bounces ................................. 79

General tips ....................................80

Beveling .............................................. 80

Estimating light intensities using Photo-shop ................................................... 81

Interiors:LIGHTING INTERIOR SCENES

Lighting interiors is very different to lighting exteriors.Some guidelines are given and explained here



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Lighting interiors poses different questions to be answered and different situations to be solved than lighting exteriors. Of course, many of the same principles apply, and there isn’t always a clear-cut distinction between inte-riors and exteriors.

One of the things we will have to concern ourselves with is the proper light-ing of the whole interior scene without overdoing it. It is easy to have underlit and overlit areas in the same scene.

Because the possibilities are far greater than in the case of exteriors and the generalities are less, rather than discussing some general principles, we will light different interior scenes in varying conditions.

Lighting a simple interior

Let us begin by creating a very simple interior scene with no windows or textures, made entirely out of cubes and fi lled rectangles.

This is a totally closed volume: no light enters is, and we cannot see inside it, unless we get a camera in there.

I have found that for interiors, it is often useful to use shorter “camera lens-es.” The preset 50 mm Strata 3D cameras are too long and usually fail to capture the whole room at the scale I work.



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Even with a camera inside the room there is not much to be seen unless we light the interior. The default global light is not entering this room, so we can convert it into a construction light or altogether delete it.

The fi rst light

Let us bring light into our room as a point light.

Let us start by using a default point light (95% intensity, white color, default full intensity distance and maximum falloff distance) more or less in the cen-ter of the room close to the ceiling.



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The ceiling problem

The point light we added seems to light everything but the ceiling. We can check this by doing a rendering.

The ceiling is not lit as expected

Indeed, we have a problem. The whole room is lit except for the ceiling. This is a common problem when doing Raytracing renderings.

If we do a Raydiosity rendering, we will see that everything is perfectly lit.

A Raydiosity rendering does not show any problem

Of course, we do not always have the time or processor) horsepower to do a Raydiosity rendering, so we will fi nd a workaround for having a properly lit ceiling in raytracing.



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A solution to the ceiling problem

A good fi x for the Raytraced ceiling problem is applying a texture to the ceiling. The lack of lighting is compensated by a glow value (0.4 in this ex-ample).

This glowing texture solves the black ceiling problem. Now the ceiling looks normal, and we do not have the long Raydiosity render times.

Have a care to eliminate the glow when trying a Raydiosity render. Remem-ber that in Raydiosity glowing surfaces are light emitters.



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Lighting the scene more evenly

We have one point light that is working well after fi xing the ceiling. However, the light is not evenly distributed in the room.

To make the handling of lights easier, we’ll make a new shape containing and replacing the light we now have.

Creating a shape with the basic light

Inside the shape window, create a cube of a size that is comfortable for you to handle (most of the time I use 1x1x1 in.), center the point light in the cube and convert the cube into a construction object. The whole point of having the cube there is to make selecting and moving our point light more easily. Besides, if the cube is not converted into a construction object, the point light will not light anything.

Lower the intensity of the light to about 15% because we will use several copies of this shape to light the room evenly.

Close the shape window, and in the scene window, replicate the light shape until there are 6 evenly distributed light sources.

The cubes surrounding the point lights are visible only in modeling views, not in the render

The cubes will be visible in the modeling window but will not appear in the render. With these six point lights we should obtain a good, even light in the room.



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Six point lights give us a good overall lighting

Textures and objects

Now that our simple, empty room is well lit, it is time to add textures and objects. For this exercise, library objects will be used.

Let us begin by applying the Cedar Parquet texture to the fl oor.

The point lights cast some specular highlights in the shiny fl oor

Next, some library shapes will furnish the room: a couple dressers, a couple tables and some chairs should be enough for this exercise.

A light yellow texture with a little specularity was added to the walls. On top of it, a corrosion shader with very low bump and mapped very small was applied.



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Hard shadows are not very helpful

Things look pretty good, but the hard shadows projected by the lights are not helping much.

A soft shadow render of the same scene will take considerably longer but will be much more believable.

The fi nished exercise

We have managed to obtain a well lit room, but there are no lamps in it.

The next exercise adds lamps to our room.

Adding lamps

This exercise expands on the previous one.

The previous exercise shows a room that is well lit, but no light sources are visible. This time we will add some lamps and set them up.



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The starting point

We will use the same room we had before.

The point lights that light this scene will be modifi ed:

Open the shape and lower the intensity of the point light to 5%Uncheck the Shadows checkboxAdd a little yellow cast to the light

This is the starting point for our exercise

With these modifi cations out room is lit at a low intensity, so there are no dark areas, and at the same time there is space to experiment with other lights to give our room a more believable look.

Adding and adjusting a lamp

We will add the Lamp that comes in the Household items shape library on top of one of the dressers.

To do this, I fi nd that the most comfortable way to work is selecting and grouping the dresser and then double-clicking it, to get it to appear in its own editing window.

Then drag the lamp shape and scale and position to suit proportions on the scene.

A render should look like this.

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Lamp shape applied to the scene

There is a need for modifi cations. Some points to consider include:

Light color: The default orange color this shape has the color tempera-ture of a candle or a very low intensity light bulb. The scene will benefi t from a higher color temperature. Let us change the color from orange to light orange-yellowIntensity: The light intensity is a bit high for the scene. Let us reduce it to 60%Total falloff: reducing it to 15 in. will help limit the area of infl uence of this light.Shade color: Changed to yellow.

The adjusted lamp gives a more believable light, like in the

The adjusted lamp

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Adding a fl oor lamp

We will add a fl oor lamp on the right. We’ll add a fl oor lamp that lights the room by bouncing light off the wall and ceiling. We’ll simulate this bounce to avoid being tied to Raydiosity.

Modeling the lamp

First thing we’ll do is model the lamp. For this example We will create a simple profi le for lathing.

Create a new, empty shape. Name it fl oor lamp or something equally creative.In the shape editing window, front view, draw a profi le for the body of the lamp.Lathe the profi le.Draw a second profi le for the glass portion of the lamp. Lathe itCreate and apply textures to the body and the upper part.

The lamp is modeled. We now need to apply the lights inside of it.

The main light

We will use point lights for this lamp, even thought at fi rst sigh it looks better suited for using a spotlight.

We’ll use a very small radius point light to produce tight shadows. In the ex-ample the light radius is set to 0.1 in. The shadows cast by this light will be fairly tight shadows, coming as they are from a small source.

We need another light to fi nish this lamp, a point light that mimics light bouncing off the wall to light the scene.

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Simulating a bounced light

The light that is bounced off the wall to light the scene will be simulated with another point light, whiter in color that the other light.

The radius of this point light will be larger, to simulate the more diffuse light coming from the wall. 2 in. is a good value.

Notice the difference between the two lamps

Exterior light

Let us now add a window to our scene. Exterior sunlight (or moonlight, or artifi cial light)

Creating the “window”

For this exercise we will create a window in the wall. A good way to do it is using Subdivision modelling.

Select the wall.Convert to Polygon MeshIn the reshape window, select the “interior“ and “exterior“ faces of the wall.Using the extrude tool, inset the wall faces.Bridge the selected facesAdjust the “window“ size and position to taste.

This is a good moment to add a visible environment. We are looking out the window, and now all we have is the black default background.

The image below shows a Horizon visible environment.

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Perforated window and visible background

Adding a “sun”

We will use a distant spotlight for the sun, in case we want to have soft shadows.

There is defi nitely a trial and error process in positioning



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Front and top view of the “sun” spotlight

Experimenting with the light positioning is a process of trial and error

Adding a gel and moving the camera

A light gel may be a good idea to enliven the scene. For this exercise a new gel was created from the image we used in last chapter to cast shadows for the exterior lights.

Besides adding the gel, the camera was moved so that more of the wall that receives the sunlight is visible in the rendering. Again, this is a trial and error process.

Optional volumetrics

A little fog adds to the realism of the scene.



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It also increases the rendering times, so we need to be careful. In this case, a light yellow Fog was added to the spotlight, with the Cast Shadows option enabled.

Nighttime

For the same view set to nighttime, the visible background is changed, the color and intensity of the spotlight are changed and the fog (if present) is deleted or edited.

For this example let us alter the intensity of the spotlight to 40%, change the color to light blue and delete the volumetric texture.

We should get an image similar to the one below.

By editing the spotlight parameters we can create a night scene.



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Raydiosity

Raydiosity is a renderer that —at the cost of rendering time— gives more realistic results than Raytracing because it calculates phenomena that Ray-tracing does not take into account.

Let us use an empty room with only a spotlight shining light through an open window. The Raytraced rendering looks like the image below.

Raytraced rendering of a room with only an external light source

Only where the light enters directly we can see something. That is the nature of Raytracing.

Raydiosity, on the other hand, can do diffuse interillumination, that is, cal-culating the diffuse refl ection of light and use that to light other areas of the scene. The image below is rendered with (more or less) default Raydiosity settings. Notice how there is some weak lighting in areas where there wasn’t any light previously. This is because diffuse interillumination is being taken into account.

Same room, same light source, Raydiosity render

If we have the time, it is profi table to use Raydiosity in our renderings. We shall explore some of the variables that infl uence our rendering time and results.



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This section is not meant to be a detailed explanation of Raydiosity set-tings: The Art & Science of Strata 3D CX CD by Chris Tyler is a very good resource for that kind of information. Here we’ll only touch on some settings that will be of use when rendering interiors.

Collected light amplifi er

The collected light amplifi er controls the brightness of the image.

Values of less than 1.0 darken the image.A value of 1.0 does not affect the imageValues larger than 1.0 lighten the image.

Collected light amplifi er values of 1.0, 1.2, 2 and 5

Diffuse bounces

Diffuse bounces determines how many times the renderer will let a ray of light that undergoes diffuse refl ection bounce.

One, two, four and eight diffuse bounces.

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The default value is one diffuse bounce. This may be insuffi cient for showing all the available detail, particularly in scenes with few light sources.

More is not always better. See the image above and notice that with 8 dif-fuse bounces the scene is over lit.

Keep in mind that less light is required to light a raydiosity scene than a raytracing scene.Less fi ll lights are required in Raydiosity than in Raytracing Remember that glowing surfaces emit light in Raydiosity

Raydiosity rendered scene

General tips

There are some general ideas and quick tips that are very useful when light-ing scenes: We’ll touch some of them here.

Beveling

Sharp edges cannot give back light. If the edge has a little bevel, light will be refl ected off it, and will help to defi ne the areas of our models and add interest to the scene.

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A scene without any beveling

A scene with a little beveling in the wall and table corners. Notice how we get a better defi nition of shapes.

Estimating light intensities using Photoshop

A quick way to estimate the light intensities for lighting a scene after we have decided how many light sources we’ll have is rendering the lights separately and then superimposing those images in Photoshop in screen mode and there manipulate their transparency to look for a good light balance.

This is nos as accurate as rendering the actual image, but it is much faster.

Rendering the base images

The fi rst thing is render the base images set to an intensity of 100%.

For the base lighting (the six instances of the point light inside a construc-tion cube), the total intensity should be 100%, so the intensity of each point light will be set to 16.66%



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Also, the point lights inside the shapes of the lamp and fl oor lamp are hid-den.

The render obtained is below.

Base lights set to 100% total intensity

For the lamp we hide the point lights used in the fl oor lamp and also hide the point light inside the cube.

We also set the intensity of the point light in the lamp to 100%

Lamp set to 100% intensity

The last image is the fl oor lamp. As before we hide all the other lights and set the intensity of the point lights to 100%



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Floor lamp at 100% intensity

We now open these three images in Photoshop, SHIFT+drag (to place them centered in the document) them to a new document of appropriate size and set them to screen mode.

All layers set to screen mode, 100% opacity

Now all we have to do is play with the opacity of the layers to estimate how a light with an intensity equal to the opacity of the layer will impact the light-ing of the scene.

Bear in mind that this is just an estimation and that the result we will get will be different from the estimation. The images below show the quick estimate and the real rendered image. Helpful, but not accurate.



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All lights estimated to 50% in Photoshop

All lights set to 50% rendered in Strata 3D

Chapter ContentIntroduction ....................................86

Three-point lighting ........................86

Creating the scene ............................. 86

Main light ............................................ 87

Fill Light .............................................. 88

Back Light .......................................... 90

Soft light and hard light ..................93

Lighting for Raydiosity ...................94

Lightdomes and HDRI ........................ 95

Area lights .......................................... 97

Important things to consider ........103

Bevel ................................................ 103

Environments ................................... 104

Caustics ........................................... 105

The End ........................................108

Objects:HOW TO LIGHT OBJECTS

Lighting objects is different (again) than lighting exteriors or interiors.We will see some lighting setups here



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Introduction

In this chapter we will discuss how to light objects, mimicking what we would do in a photo studio.

We will discuss the basics of theatrical lighting and see how to add environ-ments and effects to our object lighting.

Three-point lighting

We will begin by creating a scene and add lights to it in what is called “the-atrical” or “three point” lighting. This lighting scheme works as follows:

The subject is lit by the main lightDeep shadows are dispelled by the lower intensity fi ll light, that enables us to see detail in the shadow areasThe subject is separated from the background by the back light.

Creating the scene

Let us light a simple subject: a coffee grinder.

The coffee grinder is se in the scene and a camera is added for better con-trol of the view.

The grinder with Strata’s default light

The scene’s default global light does not give us enough control for properly lighting our object. We need to delete the global light to start from scratch.

After doing this we begin adding spotlights to light our object.

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Main light

Let us start by adding a spotlight that will be the main light source for our object. The reason why we use a spotlight is that the spotlight is much more controllable than either a global light or a point light concerning intensity, falloff, angle, gels, etc.

Position

Usually (but not always) the main light is set to the left and above the object, in an angle of 15 to 45 degrees to the left and 15 to 45 degrees upwards.

Intensity

A good number to begin setting the light intensity would be 80% We may change this value later depending on what kind of image we are after.

It is a good idea to make the spotlight point to the grinder. In this way we make sure the light is always

Falloff

When using spotlights, it is important to keep falloff in mind. If the main light is set away from the object it is lighting, the light cast by the spotlight will have lost intensity by the moment in which it reaches the object.

The spotlight falloff may cause insuffi cient light to reach the object.

Correcting the full intensity distance is a good solution.

Modifying the full intensity distance of the light, either numerically or by drag-ging the red square closest to the spotlight icon is a good way to control the intensity of the light that reaches the object being lit.

In the example the mail light was placed away from the object, so the full intensity distance was set to a fairly large value (40 in.) to allow enough light to reach the grinder.

The need for a fi ll light

The main light is lighting the grinder, or rather only the parts of the grinder that receive light directly. The parts that are left in shadow do not show any detail.



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Of course this is not desirable in our renders. A second light, less intense than the fi rst is needed here to dispel the dark shadows in the unlit areas. This second light is called a Fill light.

Fill Light

In order to see detail in the areas that remain unlit by the main spotlight, we will use a second spotlight, called the Fill light. This fi ll light is less intense than the main light and is usually placed on the other side of the camera.

A fi ll light is added

Position

The fi ll light usually goes on the opposite side of the camera to the main light, at an angle between 0 and 30 degrees upwards and 15 to 60 degrees to the right.

Main light

F i l l

Front view of the positions of the main and fi ll lights.



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Main light

F i l l

Top view of the positions of main and fi ll lights.

Shadows

The fi ll light does add detail in the unlit areas, but is now creating a second set of shadows that can be confusing. It is best to uncheck the shadows check box for the fi ll light.

Lack of shadows in the fi ll light makes the image less confusing

The Fill light now adds detail without adding confusion.

Main-fi ll ratio

The intensity ratio between main and fi ll lights is one of the decisions we have to make when creating an image. It is important to keep in mind that, when using three-point lighting, the function of the fi ll light is just to make detail visible in areas not touched by the main light.

The fi ll light then, should not be so strong as to compete with the main light, nor should it be so weak that it does not fulfi ll its function.



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A comparatively strong fi ll light lightens the shadows and generally lightens the mood of the whole image.A comparatively weak fi ll light causes dark shadows and adds drama and darkens the mood of the image.

The image below shows different main-fi ll ratios, from 1:1 to 11:1.

Notice how in the fi rst image the main light and the fi ll light compete against each other, and we do not know where the main light is coming from.

Different main-fi ll ratios: 1:1, 2:1, 4:1, 11:1

The second image has a 2:1 ratio. It is more noticeable where the main light comes from and the shadows are slightly darker.

The third image has a 4:1 ratio, with a higher contrast between light and shadow.

The fourth image has a 11:1 ratio with a very weak fi ll light. The image almost looks as if it had no fi ll light.

Back Light

Sometimes there is a need to bring the subject apart from the background. To accomplish this, one or more lights are put behind the object (from the camera point of view) to create a rim of light on the edges of the object.

Again, a spotlight will be used.

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Main lightFill light

Top view of the back light positioning

Main light

Fill light

Side view of the back light positioning

Placing the backlight is a matter of trial and error. Once the back light is ad-equately positioned, there will be a rim of light separating the lit object from the background.

The global light replaced with the main spotlight

Main light



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Bump and back lights

A bump applied to the object helps to break up the border of the rim of light that is caused by the back light.

Detail: back light, no bump

For this example a Corrosion shader is used on top of the metal texture. This corrosion shader has no hole or resistant area, and is mapped cubically to 0.1 size and 10% coverage. This gives us a really small bump that softens the hard line caused by the back light.

Detail: back light, corrosion texture set to 1.0 bump amplitude

The size and bump amplitude will determine how much the hard edge of the back light will be softened.

There is a danger of overdoing the bump amplitude, which can lend our materials an overly grainy appearance. Besides, the larger the amplitude, the slower the render.

B a c k

Back light



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Detail: back light, corrosion texture set to 0.5, 1.0, 2.0, 5.0 bump amplitude

Soft light and hard light



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Different main light radii: 0.5 in, 1 in, 2 in, 5 in, 10 in.

Lighting for Raydiosity

While reviewing three point lighting we worked with Raytracing and obtained very good results with it. Strata 3D also offers us the Raydiosity renderer which —at the price of speed— gives us a much more realistic result.

There are differences between lighting for these two renderers, which we’ll explore in this section.

Lighting that works well in Raytracing may be over illuminated in Raydiosity



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Raydiosity render with only one spotlight

Raydiosity takes more light into account than Raytracing. This means that a scene that has been properly lit for Raytracing will almost always be over illuminated in Raydiosity.

Often, a single spotlight will be enough to properly light an object in Raydios-ity.

Lightdomes and HDRI

Another way to light for Raydiosity is using a lightdome and an HDRI-based background for the lightdome.

For this example, the Soho hdr background (available at www.stratacafe.com) will be used as a background.

Render using an HDRI background as lightdome

This fi rst render is not very encouraging. This happens because the parts of the image that cast light are behind the curtain. We need to rotate the light-dome to have proper lighting.



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From the top view in the modeling window we can see that the part of the lightdome that casts the most light is behind the curtain. Rotating the light-dome 135˚ gives our scene much more light.

Rotating the lightdome

Rendering with the ightdome rotated 135 degrees

Too much light from the lightdome does not allow the detain in the curtain to be seen. Decreasing the intensity of the lightdome will bring the detail back



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Lightdome intensity decreased to 75%, 50% and 25%

Specular highlights are lost when using lightdomes for lighting. Combining a lightdome with a spotlight will give us global illumination and specular highlights at the same time.

Lightdome and spotlight for specular highlights

Area lights

Another way to use the features of the Raydiosity renderer is using area lights to light our scenes.

Any object can be an area light. The light is cast by a texture that has a glow value applied. Glow values cast light only if we are using Raydiosity for our rendering.



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To explore area lights, a 40 x 40 fi lled square is placed on top of the grinder, out of the camera view. This will be our area light.

Panel in place

A new image texture with a glow value of 1.0 will suffi ce to begin playing with lighting. A Raydiosity render of the scene with the panel in place and all other sources of light hidden should look more or less like the image below.

Glow panel in place: 40 x 40 in, glow intensity: 1.0

There is indeed light coming from the panel and lighting our scene. Some changes are in order. First thing will be softening the edges of the glow panel to avoid banding and to soften the refl ections.



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Softening the edges

The softening will be accomplished by a stencil map. A new Photoshop document, 512 x 512 pixels will do.

New Photoshop document

The stencil map will be a blurry white square on a black background. Away to make it is fi lling the image with black, then drawing a square selection, inverting the contents, deselecting, and applying Gaussian blur to taste. The result should look more or less like the image below.

This image goes into the stencil channel of the glowing texture we made for the panel



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The stencil map in place.

A rendering shows the difference.

Glow panel with a soft edge

A close up detail shows the difference even more.



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When reducing the size of the panel (with the stencil map) the intensity of the light varies. This should be compensated by increasing the glow value of the texture.

Glow intensity

At this stage, the intensity of the glow panel does not light the grinder well. This was done on purpose to see the effect of the glow value in the lighting intensity.

The images below show the scene being lit by a glow panel with glow values of 1.0, 2.0 and 5.0. In the three cases, the glow panel is very close to the grinder, and in the 5.0 glow example, too much light is falling on the top of the curtain. It is important to control the distance of the glow panel: if it is too close, too much light will fall on parts of our image; if it is too far away not enough light will reach our scene (falloff also applies here).



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Glow intensity values of 1.0, 2.0 and 5.0

The glow intensity of the texture controls how intense the light is. Another way to control the intensity of the light cast by an area light is modifying its size.

The images below show the effect of an area light 40 x 40 inches and an area light 80 x 80 inches, with all other parameters remaining the same.

40 x 40 and 80 x 80 area lights

Area lights do not produce any specular highlights. To counter this, a spot-light placed in combination with the glow panel will give us the effect and refl ections of the area light and the specular highlights of the spotlight.



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Rotated glow panel

The image below shows a glow panel and a spotlight in place. Notice the detail in the curtain.

Lightdome and spotlight for specular highlights

Important things to consider

Some important things to consider when lighting objects to increase the realism of the render.

Bevel

Bevels refl ect light and help defi ne the edges of objects and to give them volume.



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Either by bevelling in the subdivision modeler, using the fi llet extension or adding details by hand manipulating bezier elements to add curves on the edges, added detail on the edges will benefi t the fi nal work.

Adding detail and beveling edges creates interesting refl ections

Environments

Never forget to add an environment to the scene.

Either by using a refl ected environment, or off-camera glow panels, or both, the fi nal image or animation will benefi t greatly.

Render without any refl ected environment



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Same scene with a refl ected environment

Caustics

As we saw in the fi rst chapter, caustics are concentrations of light caused by refl ection or transmission/refraction.

Caustics require a spotlight or point light to be produced.

Base image for exploring caustics

Caustics also need to be activated in the render, either by using the available presets or by manually editing the Expert Raytracing parameters.



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Caustics require spotlights or point lights and have to be activated in the render



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Caustics brightness

Caustics brightness allows us to control how bright will our caustics be. Depending on the scene good values fl uctuate from 1.0 to 5.0.

Caustics brightness controls the brightness of the caustics.Caustics brightness 1.0, 2.0 and 5.0



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Photon map size

The photon map size defi nes how detailed our caustics will be. The larger the map, the more detailed the caustics, and the longer the render will take. Smaller maps render faster but the caustics obtained will not be as de-tailed.

Photon map size controls the detail of the caustics. Photon Map sizes 1.0, 2.0, 4.0

and 8.0

The End

Here ends this overview of working with light in Strata 3D. We barely scratched the surface of what can be done with the program, but it is my hope that good groundwork was laid. Hope you fi nd this document useful.

enlightenment in strata 3d cx

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