digital photography: fundamentals of light, color and ... · 12-09-2006 ©michael j. glagola 2006 2...
TRANSCRIPT
12-09-2006 ©Michael J. Glagola 2006 2
Digital Photography: Fundamentals of Light, Color,
& Exposure – Part II
Michael J. Glagola - December 9, 2006
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- OR -Why does the
picture look like that?! (Part II)
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Why is Light, Color, and Exposure IMPORTANT?
• Image editing software cannot fix every image; some digital images are beyond repair! (Garbage in = Garbage out)
• Examples:– Image too dark; black values the same– Image too light; white values the same– White balance is off; entire image has a
distinct color tint where it should not be• A technically “good” image makes it easier to
use all of the other technology of digital imaging to achieve a “great” picture
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Session Goals• To provide an understanding of the
basics of:• Light and how it effects exposure• Color and how it effects white balance• How to take better exposed and white
balanced images• How to deal with common problems with
lighting and white balance
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Agenda• What is Light• Review Exposure• What is Color; What is White Balance?• Digital Camera Exposure and White
Balance• Examples and Suggestions• Q&A
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What is Light and Color?• Electromagnetic radiation with wavelengths between about 380 and
700 nanometers is known as light. The eye has three classes of color-sensitive light receptors called cones, which respond roughly to red, blue and green light (~ 650, 530 and 460 nm, respectively)
• A range of colors can be reproduced by one of two complimentary approaches: – Additive color: Combine light sources, starting with darkness
(black). The additive primary colors are red (R), green (G), and blue (B). Adding R and G light makes yellow (Y). Similarly, G + B = cyan (C) and R + B = magenta (M). Combining all three additive primaries makes white.
– Subtractive color: Illuminate objects that contain dyes or pigments that remove portions of the visible spectrum. The objects may either transmit light (transparencies) or reflect light (paper, for example). The subtractive primaries are C, M and Y. Cyan absorbs red; hence C is sometimes called "minus red" (-R). Similarly, M is -G and Y is -B.
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Components of Light
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Photography• Using light to make pictures• Painting with light • the process of recording images by
exposing light-sensitive film or a digital sensor array to the light reflected off a scene
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Seeing Light and Color• The human eye compensates for both the
intensity of the light and its color; regardless of the light the human eye sees color consistently
• Both film and digital arrays have varying sensitivity to the amounts of light and different light frequencies. Their response to light and color does NOT match that of the human eye.
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Lighting/Exposure Recap• NO digital camera on Auto can handle all lighting
situations; problem occurs when the scene is significantly darker or lighter than 12% GRAY– If scene is lighter than 12% gray add light (+EV)– If scene is darker than 12% gray subtract light (-EV)– Be aware that high contract in the scene may exceed
the latitude of the digital sensor to such a extent that it CANNOT be fixed in software alone; consider bracketing
• Learn to recognize difficult lighting situations and experiment to find what works
• Analyze your “problem” pictures and learn from them
• Practice, Practice, Practice!!!!!!!!!!!!!!
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• Since digital camera do not see color the same way as the human eye the question is how to get the best color possible?– Solution One – Fix the color in software– Solution Two – expose the image correctly and
avoid/minimize the extra effort• Digital Cameras today have automatic white
balance. Just like digital camera’s reflective light meters it works most of the time but it can be fooled by colors in the background. Also, being automatic, the white balance may vary from scene to scene and may not be consistent! This makes digital editing more difficult.
Color and Digital Photography
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Color Balance• Color Balance is achieved when an image is
rendered close to how the eye perceives it. By setting the White Balance in your camera to match your light source, you can achieve "accurate" color Balance.
• In a film camera color balance is achieved by matching the film type to the lighting. Daylight film with day light; Tungsten film with incandescent lighting; etc.
• In a digital camera color balance is achieved by setting the white balance of the camera to match the lighting situation. This can be done with Auto WB, Manual WB, or Preset WB settings.
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Components of Light
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Color Terminology
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White Balance Settings
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Auto & Manual White BalanceAuto White Balance - Reflective
Measurement
White Card
Manual White Balance –” Incident Measurement”
• Auto WB tries to “figure out” the correct White Balance based on the light reflected from the scene
• Manual WB tries to “figure out” the White Balance based on reflectance from a “known white object”.
• Manual WB is not as dependant upon the light falling on the subject as incident metering
• Both WB processes assume the lighting is “nearly white” and does not have a strong component color
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White Balance DeterminationNormal Situation
The light reflected from the scene is the same as the light coming from the source
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White Balance DeterminationProblem Situation
The light reflected from the scene is NOT the same as the light coming from the source
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Color Examples Test Setup• Series of
photos of a Macbeth Color Checker taken under light identical conditions with only change being the WB setting of the camera
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“Auto” White Balance Example IWhite on Red Background
Auto White Balance
Manual White Balance
The white object, the tungsten light and the red background causes the Auto White Balance to set White with too much red in it, thus causing the white object to appear with a red tint.
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“Auto” White Balance Example IITungsten Light - Red Background
The red background and tungsten light causes the Auto White Balance to set the White Balance with too much red
Auto WB Manual WB
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“Auto” White Balance Example IITungsten Light - Red Background
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“Auto” White Balance Example IIITungsten Light - Blue Background
The tungsten light and the blue background causes the Auto White Balance to set the White Balance with way too little blue and too much red
Auto WB Manual WB
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“Auto” White Balance Example IIITungsten Light - Blue Background
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White Balance Example IVAuto White
Balance
Manual White
Balance
Auto White Balance is influenced by BOTH the color temperature of light and strong
background color
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Color Balance Fixes(instead of Auto White Balance)
• Preset - select the white balance Preset that most closely matches the lighting conditions
• Manual White Balance – use the manual white balance setting, fill the frame with the sheet of white paper and set the white balance for that lighting
• RAW – Shoot using RAW format; The file is unprocessed, so you can use image editing software to apply the appropriate white balance.
• Quick fix in software - adjust color in image-editing software using some “canned” adjustment algorithm Generally good but far from best.
• Slow fix in Software - adjust the color individually in image editing software.
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White Balance Example V Day Light
Sunny Cloudy
Tungsten
Manual WBAuto WB
Day FL Day-White FL
Cool-White FL
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White Balance Example VI Tungsten Light (Quartz)
Sunny Cloudy
Tungsten
Manual WBAuto WB
Day FL Day-White FL
Cool-White FL
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White Balance Example VII Fluorescent Light
Sunny Cloudy
Tungsten
Manual WBAuto WB
Day FL Day-White FL
Cool-White FL
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White Balance Tips• AWB is fine if the scene is a mix of colors but be aware that
with AWB the white balance will change slightly for each and every photograph
• When the background is strong in one color consider shutting AWB OFF; use a pre-set setting (Tungsten, Sunny, etc.) based on conditions or use Manual White Balance
• When the light temperature changes significantly you must either change the Preset White Balance Setting or reset the Manual White Balance. Be aware of:– Indoors lighting changes (e.g. Tungsten to Fluorescent)– Outdoors sunlight changes (morning or evening light,
cloudy sky, shadow)• Remember White Balance IS a matter of taste!• Preview the White Balance on the digital camera’s LCD to
get a feel for how the White Balance settings will look
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Color Balance/White Balance Recap• “White” light is not necessarily “white”. While not
very noticeable to the human eye it is to digital camera; be alert for white balance problems.
• NO digital camera on Auto can handle all lighting situations; light with a lot of “color” in it may give the auto white balance of a digital camera fits; rather than using Auto White Balance consider the Manual or Preset White Balance settings.
• Learn to recognize difficult lighting situations and experiment to find what works for your eye and your camera.
• Analyze your “problem” images and learn from them.
• Practice, Practice, Practice!!!!!!!!!!!!!!
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Summary• Digital image manipulation is the
equivalent of the film darkroom; it can fix a lot of problems but it is not a universal remedy. It helps to have a correctly exposed and white balanced image to start with.
• To take good images under difficult lighting conditions requires an understanding of the fundamentals of light and color.
• Strive to get as good an original image as possible; learn how to recognize and deal with difficult lighting and color situations rather than leave the camera on “auto”.
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Recommended Reading
• How to Take Good Pictures (Kodak)
• Nat’l Geographic Photography Field Guide
• The Hand Exposure Meter Book• Light – Working with Available
and Photographic Lighting
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A Final Thought
• There is nothing wrong with the AUTO features of your camera; just be sure you know when to turn the AUTO features off!
• Remember that what constitutes a “good” picture technically may have nothing to do with what you are trying to do in the picture; guidelines and tips are just that. They are not written in stone
• Photography is “painting with light”; the better you understand and know how to use the tools of photography the better your pictures will be
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Next Session(2nd Saturday of every Month)
Date Description1-13-07 Digital Editing Software (Vendor Presentation)2-10-07 Image Viewing Fundamentals 3-10-07 Digital Camera Picture Taking (how to get a good
digital image) 4-14-07 Printing Digital Images (Vendor Presentation)5-12-07 Good Pictures (Summary of previous sessions)
Additional Classes TBD