Color Perception and Applications SIGGRAPH 99 Course: Fundamental - PDF document

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) - R - G – G - R Achromatic Yellow – Y - B (Y = R+G) + Medium (G) (W ≅ R+G) - Y-B – W Short (B) • Characteristics – concentric receptive fields – logarithmic response of receptors – adaption

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

Final Consideration • Does this work?

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-Green-Blue Red Yellow

Color Models: Intuitive L = 1 White Green Yellow S = 1 S = 0 Cyan Red V = 1 White Green Yellow S = 1 Blue Magenta S = 0 Cyan Red Blue Magenta Hue V = 0 Hue = 0 Hue L = 0 Hue = 0 Black Black • Hue-Saturation-Value • Hue-Lightness-Saturation Color Models: Perceptually Uniform Greenish Yellow Orange Yellow Yellowish green Yellow green Yellow Orange Reddish orange Green Yellowish .500 pink Red Pink Bluish green Purplish pink White Purplish red .400 Greenish blue v' Reddish purple .300 Blue Purple .200 .100 Purplish blue • CIELUV .000 .100 .200 .300 .400 .500 .600 .700 u'

Opponent Channel Recoding Long (R) R - G - Achromatic Yellow + Medium (G) - Y-B Short (B)