Color Principles for Computer Graphics Donald House 9/17/09

Color Principles for Computer Graphics Donald House 9/17/09

Color Principles for Computer Graphics Donald House 9/17/09 Artists slides by Lynette House

Physics of Color Physiology of Color Physiology of Color

3 cone response curves Luminance efficiency Artists Color Hue

Saturation Value Value Luminance Dark to Light

Value range High key Middle key Low key Hue - Paint Mixing

Physical mix of opaque paints Primary: RYB Secondary: OGV Neutral: R + Y + B

Hue - Ink Mixing Subtractive mix of transparent inks Primary: CMY Secondary: RGB ~Black: C + M + Y

Actually use CMYK to get true black Hue - Ink Mixing Assumption: ink printed on pure white paper CMY = White RGB:

C = 1 R, M = 1 G, Y = 1 B CMYK from CMY (K is black ink): K = min(C, M, Y) C = C K, M = M K, Y = Y - K

Hue - Light Mixing Additive mix of colored lights Primary: RGB Secondary: CMY White = R + G + B

Show demonstration of optical mixing Saturation Purity of color

Perception of Color In the end, color is a perceptual phenomenon Color Constancy Perceived color is

highly context dependent Allowing color recognition with variable lighting conditions

Color Constancy Perceived color is highly context dependent Allowing color

recognition with variable lighting conditions Simultaneous Contrast

Simultaneous Contrast RGB Color Wheel

Warm/Cool Complements Split Complement

Analogous Show RGB Cube HSV Color Model RGB cube

HSV top view HSV is a projection of the RGB space HSV cone

HSV Color Model Hue, an angular measure (0 360) HSV Color Model

Saturation, a fractional measure (0.0 1.0) HSV Color Model Value, a fractional measure (0.0 1.0)

CIE 1931 Study Color Matching Experiment CIE Color Matching Functions

CIE RGB Matching Functions CIE XYZ Matching Functions RGB from Spectrum

RGB = x d

XYZ from Spectrum XYZ = x

d CIE xyY from CIE XYZ CIE xyY color model is used to catalog colors: x = X / (X + Y + Z)

y = Y / (X + Y + Z) Y = luminance CIE xyY Color Cone CIE xyY Typical Display

Gamut CIE Lu*v* and Lab Perceptually Uniform Spaces Lu*v* rescales xyY

Lab color opponents Color Picker End

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