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Color TheoryCOMP575/COMP770Dinesh Manocha
OverviewWelcome!
Today:Color representationVideo hardwareGammaColor theoryHomework
Color representationHow to store colors in the computer?
Color representationGrays
How many colors are there?How many bits are needed?
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What does the stored value represent?What if there are many more colors between these (not shown)?
Color representationGrays
Number of bits: 8, 32(int), 32(float)Colors represented: 256, 2^32 (4.3 billion)Meaning: radiant intensity, reflected intensity, arbitrary
Color representationBlues
How many bits are needed to mix blue in?What should we call the values we are storing?Should all values use the same number of bits?
Color representationBlues
Number of bits: 8, 32(int), 32(float) (per channel)Channel names: brightness, lightness, blueness, blue, gray...Colors represented: 256, 2^32 (4.3 billion) (per channel)Meaning: radiant intensity, reflected intensity, ratio of blue, arbitrary
Color representationValue representation
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Digger (1983) Crazy Cars (1987)
Bit countInteger, float
Color modelRed, green, blueCyan, magenta, yellow, blackHue, saturation, valuemore...
Format detailsPaletteChannel layoutmore...
Color representation
Battlezone (1980)1 bit, colored with red and green filters.
Color representation
CGA 4 color mode.
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Jazz Jackrabbit (1994) Descent (1994)
Color representation
CD-Man (1992)EGA 16 color mode.
Color representation
VGA 256 color mode.
Color representation
Diablo (1997)
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256 colors.
Color representationPalettes for 16 colors, 256 colors, 4096 colors, and 65536 colors.
Color representation
24 bit
Color representation
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16 bit
Color representation
12 bit
Color representation
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8 bit
Color representation
4 bit
Color representation
2 bit
Color representation
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Fig 2.4, H&B
1 bit
OverviewColor representationVideo hardwareGammaColor theoryHomework
Video hardwareCathode Ray Tube (CRT)Liquid Crystal Display (LCD)Others...
Other output include hard copies, like printouts.
Video hardwareCathode Ray Tube (CRT)
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Fig 2.4, H&B
Video hardwareCathode Ray Tube (CRT)
Video hardwareLiquid Crystal Display (LCD)
Overview
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Bottom: input, left side: output
Color representationVideo hardwareGammaColor theoryHomework
Gamma correctionResponse curve
Gamma correctionResponse curve
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Gamma correctionResponse curve
Gamma correctionWhat functions do these curves look like?
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They are similar to sqrt(x) and x^2.
Gamma correctionHumans perception is not always linear
Sound volumeWeightBrightnessWeber's law
Human perception changes with intensity.
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CameraSean McHugh - Cambridge in Colour
Eyes
Camera
Gamma correctionDevices and programs use linear dataHumans perceive logarithm data
Gamma correctionFull gray gradiant:
Linear gradiant:
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Eyes
Gamma correctionFull gray gradiant:
Gamma gradiant:
Sean McHugh - Cambridge in Colour
Gamma correctionOutput devices have their own gamma curve!Normalizes image gamma back to linear luminance
Sean McHugh - Cambridge in Colour
Gamma correctionGamma encoding
Applied when creating image
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Gamma decodingApplied at output
OverviewColor representationVideo hardwareGammaColor theoryHomework
Color TheoryMixing modesLightColor spaces
Color TheoryMixing modes
SubtractiveMixes reflective materialsRemoves light (absorption)
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Color TheoryMixing modes
AdditiveMixes emmissive materialsAdds light
Color TheoryLight
We only care about tiny visible portion
Color TheoryHuman eyes have 2 types of sensors
Rods - very sensitive, no colorCones - color
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Color TheoryCIE 1931 standard
Color TheoryCIE 1931 gamut
Color Theory
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Modern sRGB gamut
OverviewColor representationVideo hardwareGammaColor theoryHomework
HomeworkQuestions?
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