module 3: color theory & management

Module 3: Color Theory & Management 1

1

Module 3:Color Theory & Management

Instructor: Doughlas Remy


Topics Covered in This Module

Section 1

• Factors Determining Color• Characteristics of EM Radiation• Light Sources• Visible Light• The Newton Color Wheel• Quiz

Section 2

• The Ostwald Color Model• The Attributes of Color: Hue, Saturation,

and Brightness (HSB)• Color Output Models: CMYK and RGB• How CMYK Inks are Layered in Printing• How CMYK Inks Combine to Form

Composite Colors• Exercise: Halftone Screens• Quiz

Section 3

Color Schemes (optional)

Section 4

Exercises Using the HSB, CMYK, and RGB Sliders in PhotoShop

Section 5

• The CIE Color Model• The Munsell System• Quiz

Answer Forms for Printing


Section 1 • Factors Determining Color• Characteristics of EM Radiation• Light Sources• Visible Light• The Newton Color Wheel• Quiz

Section 1


Factors Determining Color (and why they matter...)

• The physics of light• Visible light represents one tiny band of the entire electromagnetic

(EM) spectrum, which also includes radio waves, microwaves, infrared and ultraviolet rays, X-rays, and Gamma rays. (More about this shortly.)

• The chemistry of matter. • Solids, liquids, and gases reflect light waves differentially.

• Solids and gases may emit light when

• heated (e.g., an electric burner coil)

• combusted (e.g., a gas explosion, logs in fireplace), or

• melted (e.g., volcanic lava).

• The physiology of human vision• Our receptors and brains vary slightly in the way they gather and

interpret color.

Section 1

Light is also emitted from electrical discharge (e.g., lightning), bioluminescence (e.g., glowworms),and chemoluminescence (e.g., lightsticks).

For other sources, see the Wikipedia List of light sources.

http://en.wikipedia.org/wiki/List_of_light_sources

http://en.wikipedia.org/wiki/List_of_light_sources



Section 1

Why color is so “wobbly” (1)

1. In a sunlit room that has two white walls, a cream-colored wall, and one green wall, pick a color from a swatch book and note its exact RGB values so that you can reproduce it later. Let’s say the color is “teal.”

2. Hold the swatch so that it is catching light reflected from one of the white walls.

3. Now turn the swatch so that it catches light reflected from the green wall. Notice the slight shift in color.

4. Turn on the florescent lights in the room. Note the slight shift in the appearance of the color on the swatch. (The RGB values haven’t changed.)

5. Close the blinds in the room and look at the swatch again (reflecting only florescent light).



Section 1

Why color is so “wobbly” (2)

6. Key the RGB values into your Photoshop color palette and fill a large square with the color. Compare it to the color swatch.

7. Print the square on your office printer. Compare the color to that of the swatch and the monitor display.

8. Using an overhead projector, project the color on a white screen. Compare.

9. Now turn off the florescent lights and view the color again. Compare.

10. Roll up the white screen and allow the projector’s light to shine on the wall, which is cream-colored. Compare the color with that of the swatch.

11. Finally, save your teal square as a PDF file and send it to a professional printer. When the proof comes back for your inspection, compare it to the swatch and to the printed output from your office printer.


Like waves in the ocean, EM waves have a crest and a trough.

The speed of the wave is constant (186,000 miles/sec).

Wavelength (distance between two crests) and amplitude (distance between crest and trough) are variable.

Characteristics of EM Radiation

Crest

Trough

Wavelength

Amplitude

Section 1


1. Wavelength (meters)

2. Amplitude (meters)

3. Frequency (cycles per second, or Hertz)

4. Temperature/Energy (electron volts, measured in Kelvins)

EM Radiation (including visible light)is measured by…

Section 1


1. Wavelength (meters)• Radio waves: 1 cm to 1 km• Microwaves: 100 microns* to 1 cm• Infrared: 1-100 microns• Visible Light: nanometers*• Ultraviolet rays (measured in kelvins only)• X-rays (measured in kelvins only)• Gamma Rays (measured in kelvins only)

2. Amplitude (meters)

3. Frequency

4. Temperature/Energy

Wavelength and Amplitude

*Micron: one-millionth of a meter.

*Nanometer: one ten-billionth of a meter

Section 1


1. Wavelength

2. Amplitude

3. Frequency (cycles per second, or Hertz) Example: Radio waves: 1kHz to 1MHz

4. Temperature/Energy

FrequencyNote The wave’s speed is constant (186,000 mi/sec), so the shorter waves have higher frequency, and vice versa.

1 sec

4 cycles per sec

2 cycles per sec

Section 1


1. Wavelength

2. Amplitude

3. Frequency

4. Temperature / Energy (electron volts, measured in Kelvins)

Temperature / Energy

Max Planck (German physicist) developed a formula for determining the spectral power distribution of a light source based on its temperature. This is called “Planck’s Law.”

Color temperature refers to the heat (or energy) of a light source. As color temperatures vary, so does the makeup of the light in terms of the relative power of its constituent wavelengths.

Section 1


1. Wavelength

2. Amplitude

3. Frequency

4. Temperature / Energy (electron volts, measured in Kelvins)• Longer wavelengths (e.g., radio waves)

are lower frequency and lower energy.• Shorter wavelengths (e.g., gamma rays)

are higher frequency and higher energy.

Temperature / Energy

Lower energy

Higher energy

Section 1


“Hotter” sources emit shorter wavelengths in larger amounts.

“Cooler” sources emit longer wavelengths in larger amounts.

Color Temperature

Note This is somewhat counter-intuitive, since we associate red with hot and blue with cold.

Section 1


• Incandescence: Solids and liquids heated to 1000K or greater emit light. (1000K = 541 degrees Fahrenheit)

• Tungsten filament light bulb (2854 K)• The Sun (5800 K on surface)• A candle flame

• Gas discharge: Gases emit light when an electric current passes through them. Variations in the density of the gas produce variations in color.

• Sodium lamps• Mercury lamps• Xenon lamps

Light Sources

Section 1

Mercury vapor lamp


• Photoluminescence: Phosphors are substances that absorb and re-emit light.

Florescence: Absorption is concurrent with re-emission.

Phosphorescence: Re-emission continues after absorption has stopped.

Note: A florescent tube is really a Mercury light coated on the inside with phosphor.

Light Sources (continued)

Section 1


The human eye is only sensitive to EM radiation at wavelengths that range roughly between 780 nanometers and 380 nanometers*. This small segment is called the visible spectrum or visible light. (Note: reptiles and insects)

*Nanometer: one ten-billionth of a meter

Visible Light

Radio wavesX-Rays

Gamma RaysInfraredUltraviolet

Visible spectrum

Section 1


• The human eye can distinguish approximately 10,000 colors.

• We call the most prominent ones, in their order, by the acronym ROY G BIV. (red, orange…)

• These are the colors as you see them refracted by a prism or in a rainbow.

• 1666: Isaac Newton experimented with a prism and concluded that “white” light is not homogeneous but rather a composite of myriad-color wavelengths.

More About Visible Light

Section 1


Newton shone white light through a prism to produce a spectrum of red, orange, yellow, green, blue, indigo, and violet beams. Then he joined the two ends of the color spectrum together to show the natural progression of colors in the form of a wheel with 360 degrees.

The Newton Color Wheel

Section 1


Newton’s color wheel was the first truly “scientific” color model because it was an empirical model—i.e., based on observation.

The Newton Color Wheel

Section 1


The Newton Color Wheel describes only hue, not saturation or brightness. The darker core of this illustration is meaningless.

Newton didn’t do saturation or brightness.

So, what do we mean by “saturation” and “brightness”?(We’ll find out in the next section...)

Section 1


Section 1 Quiz

1. Color is determined by… a. the physics of light. b. the chemistry of matter. c. the physiology of human

vision. d. (all of the above)

2. A light wave’s _____ is its only

constant characteristic. a. length b. amplitude c. crest d. speed e. trough

3. The distance between the crest

and the trough of the wave is called its “___.”

a. frequency b. wavelength c. amplitude

4. Which of these measurements is

the smallest? a. a nanometer b. a micron c. a centimeter

5. The amplitude of a wave is measured in…

a. inches b. Kelvins c. meters d. Hertz

6. The frequency of a wave is

measured in… a. inches b. Kelvins c. meters d. Hertz

7. The “temperature” of EM radiation

is measured in… a. inches b. Kelvins c. meters d. Hertz

8. Light waves with shorter

wavelengths (e.g., blue, violet) have a _____ temperature than ones with longer wavelengths (e.g., red).

a. higher b. lower

9. Which of the following are incandescent light sources?

a. Mercury lamps b. the Sun and stars c. ordinary filament light

bulbs d. candle flames

10. The spectrum of visible light runs

from… a. violet to red. b. blue to green. c. red to yellow.

11. It was ____ who discovered that

white light is composed of different-colored wavelengths.

a. Copernicus b. Ptolemy c. Isaac Newton d. Galileo e. Leonardo da Vinci

Instructions: More than one answer may be correct. Use the highlighter to mark your options. (Right-click anywhere, click Pointer Options, and then click Highlighter. When you finish, restore the arrow pointer.)

Section 1


Section 2 • The Ostwald Color Model• The Attributes of Color: Hue, Saturation,

and Brightness (HSB)• Color Output Models: CMYK and RGB• How CMYK Inks are Layered in Printing• How CMYK Inks Combine to Form

Composite Colors• Exercise: Halftone Screens• Quiz

Section 2


• dominant wavelength (hue)• purity (saturation)• luminance (brightness)

Lum

ina

nce

(B

righ

tnes

s)

*Proposed by the German scientist Ostwald in 1914, this model is useful as a tool for understanding the properties of color.

Purity (Saturation) (a measure of how far the color is from the pure hue)

Dominant Wavelength (Hue)

The Ostwald* Color Model—A Useful Tool

…characterizes color by

Section 2


The Ostwald Color Model—A Useful Tool

white

black

no hue full hue(saturation)

(brightness)

The color in each cell of the model can be expressed as the percentage of white, black and hue required on a spinning disk to produced the same perceived color.

Section 2


The Ostwald Color Model—A Useful Tool

Illustrative model (from previous slide)

Ostwald’s HSB model. PhotoShop’s color panel shows HSB values.

However, the illustrative model you’ve just seen does not identify the hue in its coding, so you will not find that model in graphics software. The HSB model, shown to the right (below), identifies the hue by its position on the color wheel (0°-360°), where both 0° and 360° are red. Notice the significance of the numbers.

Section 2


Change of HueRed (hue) in

varyingdegrees of

saturation and brightness

Adjusting Hue

Section 2


Saturation

Brightness

Hue is determined by wave length.

Brightness is determined by the amplitude of the wave.

Saturation refers to the purity of the hue.

Attributes of Color

Hue

Section 2


The visible spectrum is composed of pure (fully saturated) hues.

The spectral hues may combine to produce…

• other pure hues. (E.g., green at 520nm plus red at 66nm equals yellow at 590nm),

or

• less saturated hues. (Pink is a desaturated red insofar as it is basically white light with a greater preponderance of red wavelengths.)

+ =

More About Hue…

Section 2


Note that some fully saturated hues, e.g., magenta, are not spectral. They do not occur in the light spectrum, but they may be produced by combining other hues.

More About Hue…

Note also that some pure hues are perceived to be less saturated than others. E.g., a fully saturated yellow appears to be less saturated than a fully saturated red or violet.

magenta

Section 2


• Saturation refers to the purity of the hue. A fully saturated hue is one that contains no white.

• Brightness, also known as luminance, is determined by the amplitude of the wave. You may think of the brightness axis as progressing along an achromatic line from white through shades of grey to black. Black is simply the absence of light, whereas white is a complete mix of light.

More About Saturation and Brightness…

Section 2


HSB describes attributes.

Any color may be described in terms of its hue, saturation, and brightness, whether that color is produced by inks, by paints, by projected light, or by the bombardment of electrons against the phosphor coating on the screen of a CRT monitor.

Attributes of Color

Section 2


However, the HSB values don’t tell us how to produce (output) a certain color by using inks, paints, electrons, etc. Notice that the Photoshop HSB color panel only assigns a number (0-360) to a hue without providing any instructions to the printer, to the press, or to the monitor for producing it.

Color Output Models

Section 2


So, we need another color model for mixing inks or toners to produce full-color printed output.

Color Output Models

And we need yet another color model for mixing wavelengths of light to produce the different hues we see on our monitors.

Section 2


How a press desaturates a magenta (M) for full-color (CMYK) printing on white paper:

(1) It adds black ink (K). (desaturating toward black)

--OR--

(2) It adds equal amounts of cyan (C) and yellow (Y). (desaturating toward black)

--OR--

(3) It applies less ink to the paper, thereby allowing more white to show. (desaturating toward white)

Hue

Saturation

Brightness

Full-color printing processes use CMYK (cyan, magenta, yellow, and black) inks. CMYK is called a “substractive” color model because it creates white by subtracting (not applying) color. The white is the white of the paper.

(Magenta)

(No CMYor K inks)

Black or CMY combo

Understanding the three attributes of colorin the printing model:

Section 2


Hue

Saturation

Brightness

A monitor or slide projector works by projecting beams of red, green, and blue light (RGB) in various combinations. RGB is called the “additive” model because it achieves white by adding equal amounts of red, green, and blue.

(Magenta)

All RGB

No RGB

Understanding the three attributes of colorin the projection model:

How a color monitor desaturates a magenta:

It adds white light (which is a mix of spectral hues).

--OR--

It lowers the amplitude of the magenta wave(s).

Section 2


Inscribe an equilateral triangle in Newton’s color wheel, with “red” at the top. Which of the two output models does this triad suggest?

http://www.color-wheel-pro.com/color-theory-basics.html

Newton’s Color Wheel and the Color Output Models

Section 2


Now flip the triangle top to bottom. Which of the two output models does this triad suggest?

Newton’s Color Wheel and the Color Output Models

Note This triangle only shows C, M, and Y, which can be mixed to produce black. However, to get a really “black” black, the printing process must use black ink or toner.

Section 2


More About RGB

• The RGB model is considered additive because it achieves white by mixing red, green, and blue light in equal proportions.

• These colors are optically mixed by being placed close together or being presented in very rapid succession.

• When the wheel on the right spins, the eye does not distinguish the colors, but sees them as a composite.

• A TV screen and a computer monitor produce color pixels (picture elements) by firing red, green, and blue electron guns at phosphors on the screen in very close proximity and in very rapid succession.

Section 2


• The term additive also becomes clearer when you examine this illustration.

• Notice what “color” is at the intersection of the red, the green, and the blue circles.

• In this model, red, green, and blue are considered primary colors, and they combine to produce the secondary colors cyan, magenta, and yellow.

• You can mix red, green, and blue light in varying proportions to produce any other hue.

• Again, all hues are produced by adding red, green, and blue together.

More About RGB

Section 2


“White” light as we observe it in everyday life—e.g., in a cloud in the sky—is a mixture of all of the colors of the visible electromagnetic spectrum.

However, white light can also be produced by combining any three distinct frequencies of light as long as they are widely separated on the spectrum.

Such colors are called “primary” colors, and in the RGB model that is used for output to monitors, those colors are red, green, and blue.

RGB is simply an arbitrary choice for a triad of primary colors, and it has become a convention in computer video output more for cultural and historical reasons than for scientific ones.*

(*The prevalence of words for “red,” “green,” and “blue” throughout world languages indicates that these colors are perceived as being among the most dominant ones.)

A Note About White Light

Section 2


More About CMYK

Section 2

• CMYK is known as the subtractive model because of the way that it produces white.

• The three transparent inks used in full-color printing are cyan, magenta and yellow. When these inks are mixed in equal proportions, the result is a sort of muddy black. Black ink (or toner) is added to sharpen the black. (“K” = black)

• Remember that by default, the paper is white. So, to produce white in the printing process, we simply “subtract” the CMYK inks or toners.

• No ordinary mass printing process produces the color white on paper that is not white. This could theoretically be done, but only by applying a very thick and opaque white ink, and this would not be a cost-effective way of achieving white, particularly because press machinery is designed for thin, transparent inks.


• Here is the CMY model, where a muddy black results from overlaying the three colored inks.

• Notice here that cyan, magenta and yellow--primary colors in this model--combine to produce the secondary colors red, green and blue.

More About CMYK

Section 2


The Washington Post reported (2008) that a new paper-thin material has been developed that absorbs 99.955 percent of light that hits it, making it about 30 times as dark as the government’s current standard for blackest black, which absorbs only 98.6 percent of light.

This material, made of carbon nanotubes, will be used in solar panels (to absorb more light) and in telescopes (to sop up random bits of reflected light that don’t belong in the telescope’s canister).

“Super black” is not yet available in inks or toners, so it will not affect printed images for now.

--The Seattle Times, Feb. 21, 2008

“Super black”

Section 2


Compare the two models. Notice that the colors don’t look alike. This is because CMY cannot produce the brightness of the RGB colors. (E.g., compare the brightness of an image shown on a computer monitor and on a color print-out.)

Comparison of RGB and CMYK Output

Section 2


You just learned that, in the RGB model of mixing light, you can produce cyan bymixing blue and green together.

Logically, then, you should be able to mix redwith cyan to get white. And this is in factthe case.

Notice that red and cyan are opposite each on the colorwheel. They are what we call “complementary” colors.

Therefore, any two complementary colors will also produce white light, e.g., magenta and green , yellow and blue , etc.

A Further Note About White Light

Section 2


In printing, overlapping layers of varying percentages of transparent C, M and Y inks are used. Light passes through the inks and reflects off the surface below them (the substrate). (Black ink/toner may be added for areas that should not reflect any light.)

Each color of ink has chemical properties that allow it to absorb some wavelengths of light while reflecting others. E.g., cyan ink absorbs all the wavelengths except the cyan. So the resulting color in the illustration below is a mixture of reflected wavelengths from the CMY inks as well as the white substrate itself.

How CMYK Inks are Layered in Printing

Magenta 17%

Cyan 100%

Yellow 87%

White substrate, 100% reflectance

WHITE LIGHTREFLECTED LIGHT

Section 2


For an in-depth treatment of subtractive color, visit the “Physics Classroom” at

http://www.physicsclassroom.com/Class/light/U12L2e.html

How CMYK Inks are Layered in Printing

Section 2

http://www.physicsclassroom.com/Class/light/U12L2e.html


In printing, colors are laid down in dots. The centers of these dots are equidistant, so that the dots themselves form a grid, or “screen.”

However, the dots do not have to be completely filled with the ink. Figure 1 is an example of a (highly magnified) 50% yellow screen.

But what do we mean by “percentages” of CMY?

Figure 1

Figure 2 shows what a printed sample of the 50% yellow might look like. Notice that the yellow is lighter than the individual dots. This is because 50% of the area of each screen cell is white.

Figure 2

Section 2


Notice, too, that the color in the figure is uniform. (Figure 2) There are no gradations, as you would find in a monotone print of a photograph. (Fig. 3)

A Uniform 50% Yellow Screen

Figure 2

For gradations in the saturation of the color, you would need dots of varying sizes. Such variations can be achieved by allowing light to pass through a film negative and then through a screen to a photopolymer plate, where the light will react differentially to form raised and recessed areas for the application of the ink.

Figure 3

Section 2


This is the dark green that we saw in the earlier diagram showing the layering of inks.Note that the cyan screen at 100% prints as a solid layer and the 87% layer of yellow appears as green dots because in every case the yellow is overlaying the cyan, forming green. The magenta dots, at 17%, appear much darker because they are mostly overlaying both the cyan and yellow.

Notice, again, that the resulting color is uniform, not graduated.

How CMYK Inks Combine to Form Composite Colors

Section 2


Exercise 1: “Halftone Screens”Look carefully at the dots.

1. What colors of inks do you see?

2. Do the magenta dots vary in size?

3. Do the cyan and yellow dots vary in size?

4. Are the centers of the dots equidistant, or are they at varying distances from each other?

5. Are the “lines” (of dots) angled, or are they horizontal and vertical?

Section 2


Exercise 1: “Halftone Screens”(More about these later)

Based on the two sectors shown in white, estimate the angle of the halftone screen for magenta.

Note that each of the other three screens is at a different angle. The black (K) is usually at 45 degrees.

Section 2


Halftone Screens – 4-color


Section 2 Quiz

1. Hue is determined by... a. wave amplitude. b. wavelength. c. color temperature

2. Ostwald’s color model is useful

for understanding ... a. the CMYK model. b. complementary color

schemes c. hue, saturation, and

brightness.

3. A color’s brightness is determined by...

a. wave amplitude. b. wavelength. c. color temperature.

4. Which of the following colors is

always a desaturated hue? a. yellow b. blue c. pink d. magenta

5. When you completely desaturate a hue, you can get...

a. its complement. b. white c. total transparency d. black

6. When we combine red, green,

and blue light in equal proportions, we get...

a. black. b. white. c. sky blue. d. brown.

7. The HSB model describes color

that is produced... a. by any means. b. by inks or paints (only). c. by projected light (only). d. by computer displays

(only).

8. Using ordinary mass printing technology, what are the two conditions for producing white?

a. Use white paper. b. Apply no ink. c. Combine cyan, magenta,

and yellow in equal proportions.

d. Use white ink.

9. CMY inks must be both ___ if they are to combine to produce other hues.

a. reflectant and compatible b. compatible and water-

based c. transparent and

overlapping d. transparent and oil-based e. overlapping and reflectant

10. If all the dots in a set of CMYK

halftone screens are the same size, the printed output is...

a. a desaturated hue. b. a gradient. c. a uniform color.

Use the highlighter pointer to mark your answers. More than one answer may be correct.

Section 2


Section 3(optional)

Color Schemes


Color Schemes

Monochromatic Analogous Complementary

Split Complementary

Triadic Tetradic

Section 3


The monochromatic color scheme uses variations in brightness and saturation of a single color. This scheme looks clean and elegant. Monochromatic colors go well together, producing a soothing effect. The monochromatic scheme is very easy on the eyes, especially with blue or green hues.

A disadvantage of this scheme is its lack of contrast and vibrancy, unless blacks or dark grays are used with it.

(Note: Brightness and saturation are not shown on the color wheel.)

http://www.color-wheel-pro.com/color-theory-basics.html

Color Schemes: Monochromatic

Section 3


The analogous color scheme uses colors that are adjacent to each other on the color wheel. One color is used as a dominant color while others are used to enrich the scheme.This scheme looks richer than the monochromatic scheme, and it offers more contrast.

Color Schemes: Analogous

Section 3


The complementary color scheme consists of two colors that are opposite each other on the color wheel. This scheme looks best when you place a warm color against a cool color, for example, red versus green-blue. This scheme is intrinsically high- contrast.

Color Schemes: Complementary

Section 3


The split complementary scheme is a variation of the standard complementary scheme. It uses a color and the two colors adjacent to its complement. This provides high contrast without the strong tension of the complementary scheme.

This scheme is nuanced but difficult to balance.

Color Schemes: Split Complementary

Section 3


The triadic color scheme uses three colors equally spaced around the color wheel. This scheme is popular among artists because it offers strong visual contrast while retaining harmony and color richness. The triadic scheme is not as contrastive as the complementary scheme, but it looks more balanced and harmonious.

Color Schemes: Triadic

Section 3


The tetradic scheme is the most varied because it uses two complementary color pairs. This scheme is hard to harmonize; if all four hues are used in equal amounts, the scheme may look unbalanced, so you should choose a color to be dominant or subdue the colors.

Color Schemes: Tetradic

Section 3


Section 4 Exercises Using the HSB, CMYK, and RGB Sliders in PhotoShop


1. Start Photoshop. 2. On the File menu, click New, and then click OK.3. If the color palette (shown below) is not visible, then click Window on

the main menu, and then click Show color.4. In the top right corner of the color palette, click the small triangle to

display the menu. Then click HSB.

Exercise 2: Understanding Hue, Saturation, and Brightness

Section 4


1. Notice the symbols to the right of the number fields.2. What is the highest number in the top field?3. What is the highest number in the other two fields?

Notice the color and the hue number, as expressed in degrees.


Section 4


Use the values 0, 20, 40, 60, 80 and 100 to fill in the colored cells of the Ostwald chart.

The first number in each sequence is the hue, the second is saturation, and the third is brightness.

Note that the hue, with the number 0, does not change.


000

0100100

00

100

Section 4


Using the HSB color sliders, find the values for the following pure hues, plus black and white. Enter “x” where any value will do.

Exercise 4: Finding Pure Hues on the HSB Slider

H S B H S BRed Blue

Yellow Magenta

Green Black

Cyan White

Section 4


Now find the values for any three shades of gray.

Exercise 5: Finding Shades of Gray on the HSB Slider

H S BGray 1

Gray 2

Gray 3

Section 4


1. Select the RGB (Red, Green, Blue) slider from the drop-down menu at the arrow.

Exercise 6:Using the RGB Slider

2. What is the highest number on each slider, and what is the significance of each?

Section 4


Why 255?

RGB colors are for output from computers, which are digital devices.

Digital technology uses binary numbers. A signal may be in an “on” or an “off” state. These two states are represented as 1 and 0 and, together, they are referred to as a “bit” of information.

With two bits, we have four possible states: 10, 01, 11, or 00.

With three bits, we have eight possible states: 000, 001, 010, 011, 100, 101, 110, and 111.

Section 4


Why 255?

To determine how many possible states can be represented by “N” number of bits, just raise 2 to the power of “N.”

Example: 4 bits gives us 16 states (24), and 5 bits gives us 32 states (25).

How many states will 8 bits give us?

Section 4


Why 255?

255 is one less than 256...

Section 4

The software engineers who designed this RGB color palette wanted each slider to begin with a zero, not a “1,” so they shifted the scale back by one.

Now, with the G and B sliders at zero, slide the R slider back and forth from 0 to 255. What happens to the color?How many colors do you get?

Now set the R and B sliders to 0 and move the G slider back and forth. What happens to the green?


Why 255?

Now set the B slider to 0 and move the other two around.Describe the colors that you see.

How many colors can you produce with the R and G sliders?

How many colors can you produce all three sliders?

Section 4


Provide the RGB values for the colored cells, using the numbers 0, 51, 102, 153, 204, and 255.

You may use the Photoshop RGB slider to help in this task.

Exercise 7: Using RGB Values to Adjust Saturation and Brightness of a Pure Hue

000

25500

255255255

Section 4


Find the values for the following pure hues, plus black and white.

Exercise 8:Finding Pure Hues on the RGB Slider

R G B R G BBlack Blue

White Yellow

Red Magenta

Green Cyan

Section 4


Find the RGB values for any three different shades of gray.

Exercise 9: Finding Shades of Gray on the RGB Slider

R G BGray 1

Gray 2

Gray 3

Section 4


1. Select the CMYK slider from the drop-down menu at the arrow.

Exercise 10:Using the CMYK Slider

2. What is the highest number on each slider, and what is the significance of each?

Section 4


Provide the CMYK values for the colored cells, using the numbers 0, 20, 40, 60, 80 and 100.

You may use the Photoshop CMYK slider to help in this task.

Exercise 11: Using CMYK Values to Adjust Saturation and Brightness of a Pure Hue

000

100

0100800

0000

Section 4


Find the values for the following pure hues, plus black and white.

Exercise 12:Finding Pure Hues on the CMYK Slider

C M Y K C M Y KBlack Yellow

White Red

Cyan Green

Magenta Blue

Section 4


Now find the values for any three shades of gray.

Exercise 13: Finding Shades of Gray on the CMYK Slider

C M Y KGray 1

Gray 2

Gray 3

Section 4


Section 5 • The CIE Color Model• The Munsell System• Quiz

Section 5


• CIE was devised at Cambridge University in the early 20th century and adopted in 1931. “CIE” stands for “Commission Internationale de l’Eclairage.”

• The CIE color models (there was an original and several revisions) are based as closely as possible on how humans perceive color. They are device-independent.

• CIE researchers had to define standard (light) sources and standard observers.

CIE

Section 5


• Source A: A tungsten-filament lamp with a color temperature of 2854K.

• Source B: Noon sunlight (in Cambridge, England?), color temperature 4800K.

• Source C: Average daylight, color temperature 6500K.

These “sources,” also called “illuminants,” are defined by spectral power distribution. They are not actual physical sources of light.

CIE Standard Sources

Section 5


• The “standard observer” is actually a composite made from 15 to 20 individuals. The composite represents normal human color vision.

• The observer views a pure spectral color alongside one created by three lamps emitting varying amounts of RGB.

• When the observer thinks they match, the “tristimulus values” of the RGB lamps are assigned to the pure spectral color.

The CIE Standard Observer

Section 5


• Why the funny horseshoe shape?

• Caveat: Our output devices (monitor, projector) do not show the full range of colors, and the graphic is low-res.

• The white point at A is the achromatic point. (No hues)

• The numbers around the curve of the diagram are wavelengths (in nanometers) of all spectral hues visible to the human eye.

The CIE Diagram is an extremely precise and widely-used method of producing and identifying color since 1931. The CIE system was created by the Commission Internationale de l’Eclairage.

A

The CIE Chromaticity Diagram

Section 5


• Each color inside the curve has a precise mathematical relation to combinations of other colors within the curve. (These combinations may be represented by either straight lines or polygons.) E.g.,

• The three colors at the vertices of the white triangle combine to form the color indicated by the crosshair at B.

• Point B will be in the center of the triangle as long as the three component colors are in equal proportion.

• Notice the mint-green bar below the diagram. This shows the color at B.

• Shown just below the mint-green bar are the three colors that were combined in equal proportions to produce the color at point B.

http://www.cs.rit.edu/~ncs/color/a_chroma.html

B

CIE: A Highly Mathematical Model

Section 5


B • When three colors are mixed in different proportions (see sliders below), notice that point B moves away from the center of the triangle.

• Point B is said to represent the “Center of Gravity” of the triad.

The CIE “Center of Gravity”

Section 5


The chromaticity diagram is also used to define color gamuts, or color ranges. Gamuts are simply polygons placed on the diagram.

The CIE diagram is useful in comparing the color gamuts of monitors, printers, slide films and other hardcopy devices.

Shown here are the approximate color gamuts for computer monitors (RGB) and printers (CMYK). Actually, the red, green and blue phosphors used in monitors vary from manufacturer to manufacturer.

The color gamut of most printers is smaller than that of monitors. Setting your color quality from 24 to 16 bit in the control panel will help you match printer and monitor output more closely.

CIE Color Gamuts

Section 5


• Inconsistent color is a problem inherent in all computer-generated color output, whether to a monitor or to print.

• Every RGB device (scanner, monitor, digital camera) has itsown gamut.

• Some RGB colors cannot be reproduced in CMYK, and vice versa. (Open CIE Gamut 2 in PS, change RGB to CMYK and observe the difference. Start to save as TIFF.)

• Neither RGB nor CMYK can produce all colors visible to the human eye.

• The international standard for color output to print is known as SWOP, or Specifications for Web Offset Publications.

CIE Color Gamuts: Points to Remember

Section 5


The CIE chromaticity diagram shows only dominant wavelength and saturation.

It is independent of the amount of luminous energy (amplitude of the wave).

E.g.,

Brown is not shown on the diagram. It is just a low-luminance orange-red.

You could imagine a third axis for this diagram. It would show a range of luminance from 100% (at the surface) to 0% (black). Compare this to the color wheel we studied earlier:

Where’s Brown?

Section 5


The scientists who proposed the original CIE model found that, in order to produce certain colors visible to the human eye, some R, G or B values had to be negative. They thought this was unacceptable for an international standard, so they decided to use the letters X, Y, and Z instead. These have values represented solely by positive integers, but they correspond roughly to R, G, and B.

CIEXYZ

CIEXYZ, CIELAB, and CIELUV

Section 5


CIELAB is a 1942 revision that defines

colors along two polar axes for color (a

and b), and a third for lightness (L).

CIELAB has become very important

for desktop color. Like all CIE models,

it is device independent (unlike RGB

and CMYK), is the basic color model in

Adobe PostScript (level 2 and level 3),

and is used for color management as

the device independent model of the

ICC (International Color Consortium)

device profiles.

+a is red-a is green+b is yellow

-b is blue0 is greyscale


Section 5


A 1960 revision. It uses an altered and elongated form of the original chromaticity diagram.

CIELUV


Section 5


• Albert Henry Munsell: an American artist.• Wanted a decimal system instead of color names.• Published Color Notation in 1905.• His system is still a standard for colorimetry (the measurement

of color)• To understand this system, first we’ll take you back to the color

wheel we saw earlier:

Introduction to the Munsell System

Section 5


Munsell modeled his system as an orb (you have to imagine this) around whose equator there runs a band of pure hues corresponding to those of Newton’s color wheel.

The axis of the orb is a scale of neutral grey values with white as the north pole and black as the south pole.

Extending horizontally from the axis at each grey value is a gradation of color progressing from neutral gray to full saturation.

Munsell used the terms “hue,” “chroma,” and “value,” to describe these aspects of color. However, to avoid confusion, we’re going to stick with “hue,” “saturation,” and “brightness.”

How the Munsell System Works

Section 5


• 5 primary hues:• Red: R• Yellow: Y• Green: G• Blue: B• Purple: P

• 5 intermediate hues:• Yellow-red (YR)• Green-yellow (GY)• Blue-green (BG)• Purple-Blue (PB)• Red-Purple (RP)

Compare Newton’s wheel. How many “primary colors” are there?

The Munsell System: Hue (1)

Section 5


• Each primary and intermediate hue is allotted 10 compass degrees and then identified by its place in the segment.

• E.g., Primary red is 5R. 2.5R tends towards red-purple, and 7.5R tends towards yellow-red.

http://www.adobe.com/support/techguides/color/colormodels/munsell.html

The Munsell System: Hue (2)

Section 5


• The brightness axis controls the grey level. It runs from black (10) to white (0). E.g., 8 is a dark grey, and 2 is a light grey.

• So 5PB 6 indicates a middle purple-blue with a brightness level of 6.

The Munsell System: Brightness

Section 5


Saturation distinguishes between a pure hue and a grey shade. The saturation axis runs at a right angle to the brightness axis.

• Saturation is denoted by a number following the brightness number, separated by a slash (“/”). E.g., 7.5YR 7/12 indicates a yellow/red tending towards Y, with a brightness of 7 and a saturation of 12. It’s a sort of “salmon” color.

The Munsell System: Saturation (1)

Section 5


• You may have noticed that I did not mention the range of numbers for the saturation value.

• This is because full saturation for individual hues occurs at different places.

• E.g., 5RP, shown here, reaches full saturation at 5/26, whereas...


Section 5


• 10YR has a shorter saturation axis, with full saturation achieved at 7/10 and 6/10.


Section 5


• Munsell originally envisioned his color model as a sphere, but later saw it become radically asymmetrical.

• Note that reds, blues and purples tend to reach higher saturation values.

• Also note that these same colors reach full saturation at mid-levels on the brightness scale, while yellows and greens reach it a higher levels.


Section 5


• The Munsell system is still internationally accepted.

• The Munsell Book of Colors is sold commercially to printers and designers.

• There are also digital libraries for the Munsell system. You will find them in Adobe PageMaker and Adobe FrameMaker.

• No digital color library, however, will display accurately due to the gamut constraints of RGB.

• Printed swatches are the only way to guarantee accuracy.

• The Munsell Company is owned by GretagMacbeth and is on the web at www.munsell.com. (Take a look.)

Using the Munsell System

Section 5

http://www.munsell.com/


Section 5 Quiz

1. The range of colors that a device (monitor, printer, etc.) can handle is called its...

a. chromaticity. b. CIE. c. gamut. d. output. e. (none of the above)

2. In order to study color, CIE

researches had to define standards for...

a. light sources and observers.

b. inks and pigments. c. hue, saturation, and

brightness.

3. Which of the following devices can manage all the colors in the CIE system?

a. digital printers b. LCD monitors c. CRTs d. some digital cameras e. (none of the above)

4. CIE researchers had their observers compare pure spectral colors with...

a. Pantone colors. b. light from RGB lamps. c. sunlight. d. unsaturated spectral

colors

5. Which color model has the smallest color gamut?

a. CMYK b. RGB c. Ostwald d. Munsell e. CIELAB f. CIELUV

6. Which color model allows you to

compare color gamuts? a. Ostwald’s b. Munsell’s c. Newton’s d. CIE

7. Munsell’s color system took ___ and turned it into ___.

a. CIE ... a pyramid. b. CIE ... an orb. c. Newton’s color wheel ...

a pyramid. d. Newton’s color wheel ...

an orb.

8. Munsell’s system allowed a ___ of colors.

a. digital coding b. spectral mixing c. hypersaturation d. frequency analysis

9. A two-dimensional diagram

showing only the hues in Munsell’s system is a circle with ___ degrees.

a. 100 b. 360 c. 10,000 d. 1000 e. 256

Mark your answers on an answer sheet. More than one answer may be correct.

Section 5


End of Module 3


Slides to print out at 2 per page for handout (next 6 slides)


000

0100100

00

100


H S B H S BRed Blue

Yellow Magenta

Green Black

Cyan White

H S BGray 1

Gray 2

Gray 3


000

25500

255255255


R G B R G BBlack Blue

White Yellow

Red Magenta

Green Cyan

R G BGray 1

Gray 2

Gray 3


000

100

0100800

0000


C M Y K C M Y KBlack Yellow

White Red

Cyan Green

Magenta Blue

C M Y KGray 1

Gray 2

Gray 3


Answers to Exercises


Purity (Saturation)

Lum

inan

ce

(Brig

htne

ss)



000

0100100

00

100

060100

04060

04040

0060

020100

Section 4


Exercise 4: (answers)

Finding Pure Hues on the HSB Slider

H S B H S BRed 0 100 100 Blue 240 100 100

Yellow 60 100 100 Magenta 300 100 100

Green 120 100 100 Black x x 0

Cyan 180 100 100 White x 0 100

Section 4


Exercise 5: (Sample answers) Finding Shades of Gray on the HSB Slider

Section 4


Purity (Saturation)

Lum

inan

ce

(Brig

htne

ss)


Exercise 7: (Answers) Using RGB Values to Adjust Saturation and Brightness of a Pure Hue

000

25500

255255255

255102102

1535151

10200

153153153

255204204

100% Red+ 100% Blue+ 100% Green= White

100% Red+ 0% Blue+ 0% Green= Red

0% Red+ 0% Blue+ 0% Green= Black

Section 4


Exercise 8: (answers)

Finding Pure Hues on the RGB Slider

R G B R G BBlack 0 0 0 Blue 0 0 255

White 255 255 255 Yellow 255 255 0

Red 255 0 0 Magenta 255 0 255

Green 0 255 0 Cyan 0 255 255

Section 4


Exercise 9: (sample answers)

Finding Shades of Gray on the RGB Slider

Any set of equal RGB values (except 0,0,0 and 255,255,255) will produce a shade of gray.

Section 4


Purity (Saturation)

Lum

inan

ce

(Brig

htne

ss)


Exercise 11: (answers) Using CMYK Values to Adjust Saturation and Brightness of a Pure Hue

000

100

0100800

0000

060400

00040

0402040

0402060

Cyan: NoneMagenta: NoneYellow: NoneBlack: None

Cyan: NoneMagenta: 100%Yellow: 80%Black: None

Cyan: NoneMagenta: NoneYellow: NoneBlack: 100%

Section 4


Exercise 12: (Answers)

Finding Pure Hues on the CMYK Slider

C M Y K C M Y KBlack 100 100 100 0* Yellow 0 0 100 0

White 0 0 0 0 Red 0 100 100 0

Cyan 100 0 0 0 Green 100 0 100 0

Magenta 0 100 0 0 Blue 100 100 0 0*

*50 here makes a better blue.*Black may also have the following values: 0, 0, 0, 100, or100, 100, 100, 100.

Section 4


Exercise 13: (sample answers)

Finding Shades of Gray on the CMYK Slider

Section 4

Module 3: Color Theory & Management 123Answer forms

1. a b c d e 2. a b c d e 3. a b c d e 4. a b c d e 5. a b c d e 6. a b c d e 7. a b c d e 8. a b c d e 9. a b c d e 10. a b c d e11. a b c d e12. a b c d e13. a b c d e 14. a b c d e15. a b c d e16. a b c d e 17. a b c d e18. a b c d e19. a b c d e 20. a b c d e21. a b c d e22. a b c d e 23. a b c d e

1. a b c d e 2. a b c d e 3. a b c d e 4. a b c d e 5. a b c d e 6. a b c d e 7. a b c d e 8. a b c d e 9. a b c d e 10. a b c d e11. a b c d e12. a b c d e13. a b c d e 14. a b c d e

Module 1:Introduction

Module 2: Printing Processes Module 3:Color Theory and Mgmt

1. a b c d e 2. a b c d e 3. a b c d e 4. a b c d e 5. a b c d e 6. a b c d e 7. a b c d e 8. a b c d e 9. a b c d e 10. a b c d e11. a b c d e

1. a b c d e 2. a b c d e 3. a b c d e 4. a b c d e 5. a b c d e 6. a b c d e 7. a b c d e 8. a b c d e 9. a b c d e 10. a b c d e

Section 1

Section 2

24. a b c d e 25. a b c d e 26. a b c d e 27. a b c d e 28. a b c d e 29. a b c d e 30. a b c d e 31. a b c d e 32. a b c d e 33. a b c d e34. a b c d e35. a b c d e36. a b c d e 37. a b c d e38. a b c d e39. a b c d e 40. a b c d e41. a b c d e42. a b c d e 43. a b c d e44. a b c d e45. a b c d e 46. a b c d e

Module 3: Color Theory & Management 124Answer forms

Module 4: Tools and Techniques

1. a b c d e 2. a b c d e 3. a b c d e 4. a b c d e 5. a b c d e 6. a b c d e 7. a b c d e 8. a b c d e 9. a b c d e 10. a b c d e

Section 1


Section 2

1. a b c d e 2. a b c d e 3. a b c d e 4. a b c d e 5. a b c d e 6. a b c d e 7. a b c d e 8. a b c d e

Section 3


Section 4


Answer: 28, or 2x2x2x2x2x2x2x2, or 256.


Answer: 256 x 256 = 64,536


Answer: 256 x 256 x 256 = 16,777,216

module 3: color theory & management

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