Color Perception and Applications SIGGRAPH 99 Course: Fundamental Issues of Visual Perception for Effective Image Generation Penny Rheingans University of Maryland Baltimore County Overview Characteristics of Color Perception Mechanisms of Color Perception Color Specification Using Color to Represent Information
Characteristics of Color Perception Fundamental, independent visual process after-images color deficient vision Relative, not absolute Interactions between color and other visual properties Physiology: Receptors Rods active at low light levels (scotopic vision) only one wavelength sensitivity function Cones active at normal light levels three types: sensitivity functions with different peaks
Cone Sensitivity Functions Glassner 95, p. 16. Physiology: Ganglia Transform incoming SML into opponent color responses Long (R) G - R - R - G Y - B (Y = R+G) W (W @ R+G) Medium (G) Short (B) Characteristics concentric receptive fields logarithmic response of receptors adaption + Yellow - Achrom atic Y-B
Physiology: Brain Lateral geniculate nuclei assemble data for single side of visual field 2 monochromatic layers => magnocellular path 4 chromatic layers => parvocellular path Visual cortex visual area 1: blobs visual area 2: thick stripes visual area 4 Visual Pathway Murch, 87.
Parvocellular Division Role in vision discrimination of fine detail color Characteristics color: sensitive to wavelength variations acuity: small RF centers speed: relatively slow response Color Models Device-derived convenient for describing display device levels RGB, CMY Intuitive based in familiar color description terms HSV, HSB, HLS Perceptually uniform device independent, perceptually uniform CIELUV, CIELAB, Munsell
Color Models Device-derived convenient for describing display device levels RGB, CMY Intuitive based in familiar color description terms HSV, HSB, HLS Perceptually uniform device independent, perceptually uniform CIELUV, CIELAB, Munsell
Color Models Device-derived convenient for describing display device levels RGB, CMY Intuitive based in familiar color description terms HSV, HSB, HLS Perceptually uniform device independent, perceptually uniform CIELUV, CIELAB, Munsell
Hill et al. 97, pg. 136 Uses of Color Show classification Mimic reality Show value Draw attention Show grouping
Uses of Color Show classification Mimic reality Show value Draw attention Show grouping
Uses of Color Show classification Mimic reality Show value Draw attention Show grouping
Uses of Color Show classification Mimic reality Show value Draw attention Show grouping
Uses of Color Show classification Mimic reality Show value Draw attention Show grouping
Ware and Beatty 85, p. 22 Perceptual Distortions Color-deficiency Interactions between color components saturation - brightness (Helmholtz-Kohlraush effect) brightness - hue (Bezold-Brucke Phenomenon) Simultaneous contrast brightness hue Small field achrominance Effects of color on perceived size
Bezold-Brucke Phenomenon Hurvich 81, pg. 73. Perceptual Distortions Color-deficiency Interactions between color components saturation - brightness (Helmholtz-Kohlraush effect) brightness - hue (Bezold-Brucke Phenomenon) Simultaneous contrast brightness hue Small field achrominance Effects of color on perceived size
Simultaneous Contrast Simultaneous Contrast
Perceptual Distortions Color-deficiency Interactions between color components saturation - brightness (Helmholtz-Kohlraush effect) brightness - hue (Bezold-Brucke Phenomenon) Simultaneous contrast brightness hue Small field achrominance Effects of color on perceived size Small Field Achrominance Wandell 95, cp. 3.
Perceptual Distortions Color-deficiency Interactions between color components saturation - brightness (Helmholtz-Kohlraush effect) brightness - hue (Bezold-Brucke Phenomenon) Simultaneous contrast brightness hue Small field achrominance Effects of color on perceived size Color-size Illusion Cleveland and McGill 83.
Some Color Scales Univariate color model component optimal scales double-ended Multivariate color model components Census Bureau TVCM complementary display parameters
Some Color Scales Univariate color model component optimal scales double-ended Multivariate color model components Census Bureau TVCM complementary display parameters
Some Color Scales Univariate color model component optimal scales double-ended Multivariate color model components Census Bureau TVCM complementary display parameters Olson 97, fig. 11-8.
Some Color Scales Univariate color model component optimal scales double-ended Multivariate color model components Census Bureau TVCM complementary display parameters
Some Color Scales Univariate color model component optimal scales double-ended Multivariate color model components Census Bureau TVCM complementary display parameters Tufte 83, pg. 153.
Some Color Scales Univariate color model component optimal scales double-ended Multivariate color model components Census Bureau TVCM complementary display parameters
Evaluating Color Scales Trumbo s Principles Order: ordered values should be represented by ordered colors Separation: significantly different levels should be represented by distinguishable colors Rows and columns: to preserve univariate information, display parameters should not obscure one another Diagonal: to show positive association, displayed colors should group into three perceptual classes: diagonal, above, below
Evaluating Color Scales Trumbo s Principles Order: ordered values should be represented by ordered colors Separation: significantly different levels should be represented by distinguishable colors Rows and columns: to preserve univariate information, display parameters should not obscure one another Diagonal: to show positive association, displayed colors should group into three perceptual classes: diagonal, above, below
Evaluating Color Scales Trumbo s Principles Order: ordered values should be represented by ordered colors Separation: significantly different levels should be represented by distinguishable colors Rows and columns: to preserve univariate information, display parameters should not obscure one another Diagonal: to show positive association, displayed colors should group into three perceptual classes: diagonal, above, below
Tufte 83, pg. 153.
Evaluating Color Scales Trumbo s Principles Order: ordered values should be represented by ordered colors Separation: significantly different levels should be represented by distinguishable colors Rows and columns: to preserve univariate information, display parameters should not obscure one another Diagonal: to show positive association, displayed colors should group into three perceptual classes: diagonal, above, below
Evaluating Color Scales (cont.) Ware s experiments metric (quantitative) judgements surface (qualititative) judgements redundant color scales
Tufte 97, pg. 77. Tufte 97, pg. 76.
Ware s Color Scales Ware 88.
Considerations Consider goals Consider data Consider audience Consider color connotations
Does this work? Final Consideration
Principles of Color Representation Avoid distortions Exploit the familiar Emphasize the interesting Say it again (redundant mappings) Select appropriate level of detail
Color Models: Device-derived Blue Cyan Magenta White Black Green Red Yellow Red-Green-Blue
Color Models: Intuitive L = 1 White Green Yellow Cyan Blue S = 1 S = 0 V = 1 White Magenta Red Cyan Green S = 0 Yellow S = 1 Red Blue Magenta V = 0 Black Hue Hue = 0 L = 0 Black Hue Hue = 0 Hue-Saturation-Value Hue-Lightness-Saturation Color Models: Perceptually Uniform.500.400 v'.300.200 Yellowish green Yellow green Green Bluish green Greenish blue Blue White Greenish Yellow Orange Yellow Yellow Orange Reddish orange Yellowish pink Purple Pink Purplish pink Red Reddish purple Purplish red.100.000 Purplish blue.100.200.300.400.500.600.700 u' CIELUV
Opponent Channel Recoding Long (R) - R - G Medium (G) Short (B) + Yellow - Achromatic Y-B