Color Theory - GAMMA

1 Color TheoryCOMP575 Micah TaylorOverviewWelcome comp770!Today: Color representationVideo hardwareGammaColor theoryHomeworkColor representationHow to store colors in the computer? Color representationGraysHow many colors are there?How many bits are needed?What does the stored value represent?What if there are many more colors between these (not shown)? Color representationGraysNumber of bits: 8, 32(int), 32(float)Colors represented: 256, 2^32 ( billion)Meaning: radiant intensity, reflected intensity, arbitraryColor representationBluesHow 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 representationBluesNumber of bits: 8, 32(int), 32(float) (per channel)Channel names: brightness, lightness, blueness, blue, represented: 256, 2^32 ( billion) (per channel)Meaning.

2 Radiant intensity, reflected intensity, ratio of blue, arbitraryColor representationValue representationBit countInteger, floatColor modelRed, green, blueCyan, magenta, yellow, blackDigger (1983)Crazy Cars (1987)Hue, saturation, detailsPaletteChannel representationBattlezone (1980)1 bit, colored with red and green representationCGA 4 Color representationJazz Jackrabbit (1994)Descent (1994)CD-Man (1992)EGA 16 Color representationVGA 256 Color representationDiablo (1997)256 representationPalettes for 16 colors, 256 colors, 4096 colors, and 65536 representation24 bitColor representation16 bitColor representation12 bitColor representation8 bitColor representation4 bitColor representationColor representation2 bitColor representation1 bitOverviewColor representationVideo hardwareGammaColor theoryHomeworkVideo hardwareCathode Ray Tube (CRT)Liquid Crystal Display (LCD)Fig , H& output include hard copies, like hardwareCathode Ray Tube (CRT)Video hardwareCathode Ray Tube (CRT)Video hardwareLiquid Crystal Display (LCD)Fig , H&B Bottom: input, left side.

3 OutputOverviewColor representationVideo hardwareGammaColor theoryHomeworkGamma correctionResponse curveGamma correctionResponse curveGamma correctionResponse curveGamma correctionWhat functions do these curves look like?They are similar to sqrt(x) and x^ correctionHumans perception is not always linearSound volumeWeightBrightnessWeber's lawHuman perception changes with correction Camera Sean McHugh - Cambridge in Colour Eyes Camera EyesDevices and programs use linear dataHumans perceive logarithm dataGamma correctionFull gray gradiant: Linear gradiant: GAMMA correctionFull gray gradiant: GAMMA gradiant: Sean McHugh - Cambridge in ColourGamma correctionGamma correctionOutput devices have their own GAMMA curve!

4 Normalizes image GAMMA back to linear luminance Sean McHugh - Cambridge in ColourGamma correctionGamma encodingApplied when creating imageGamma decodingApplied at outputOverviewColor representationVideo hardwareGammaColor theoryHomeworkColor TheoryMixing modesLightColor spacesColor TheoryMixing modesSubtractiveMixes reflective materialsRemoves light (absorption) Color TheoryMixing modesAdditiveMixes emmissive materialsAdds lightColor TheoryLightWe only care about tiny visible portionROYGBV380450495570590620750 Color TheoryHuman eyes have 2 types of sensorsRods - very sensitive, no colorCones - color400450500550600650700 Wavelength (nm)Normalized cone response (linear energy)SMLC olor TheoryCIE 1931 standardColor TheoryCIE 1931 gamutColor TheoryModern sRGB gamutOverviewColor representationVideo hardwareGammaColor theoryHomeworkHomeworkQuestions?