CS 354 Understanding Color

CS 354 Understanding Color Mark Kilgard University of Texas February 21, 2012

Today’s material ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

My Office Hours ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Last time, this time ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Daily Quiz ,[object Object],[object Object],[object Object],[object Object],[object Object]

Compositing ,[object Object],[object Object],[object Object]

Intra-pixel Regions for Compositing ,[object Object],A ∩ ~B ~A ∩ B ~A ∩ ~B Source: SVG Compositing Specification

Compositing Digital Images ,[object Object],[object Object],[object Object],[object Object],[object Object]

Porter-Duff Composite Operators

Porter & Duff Modes Porter & Duff blend modes 1 1 0 0 1 1 0 1 1 0 1 0 Y 0 0 0 Clear 1 0 0 Xor 0 1 Bc Dst-atop 1 1 Ac Src-atop 1 0 0 Dst-out 0 0 0 Src-out 0 0 Bc Dst-In 0 1 Ac Src-In 1 1 Bc Dst-Over 1 1 Ac Src-Over 1 1 Bc Dst 0 1 Ac Src Z X f(Ac,Bc) Operation

Porter & Duff Modes Expanded Uncorrelated blend mode expansion of Porter & Duff blend modes 1 0 1 1 0 0 0 1 1 1 0 0 Z 1 1 0 0 1 1 0 1 1 0 1 0 Y 0 0 0 Clear Aca×(1-Ba)+(1-Aa)×Bca 0 0 Xor (1-Ba)×Aca+Aa×Bca 1 Bc Dst-atop Aca×Ba+(1-Aa)×Bca 1 Ac Src-atop (1-Aa)×Bca 0 0 Dst-out (1-Ba)×Aca 0 0 Src-out Bca×Aa 0 Bc Dst-In Aca×Ba 1 Ac Src-In Bca+(1-Ba)×Aca 1 Bc Dst-Over Aca+(1-Aa)×Bca 1 Ac Src-Over Bca 1 Bc Dst Aca 1 Ac Src Blend mode X f(Ac,Bc) Operation

Porter & Duff for glBlendFunc GL_ONE_MINS_DST_ALPHA GL_ONE_MINUS_DST_ALPHA GL_DST_ALPHA GL_ZERO GL_ONE_MINUS_DST_ALPHA GL_ZERO GL_DST_ALPHA GL_ONE_MINUS_DST_ALPHA GL_ONE GL_ZERO GL_ONE GL_ZERO srcFactor Aca×(1-Ba)+(1-Aa)×Bca (1-Ba)×Aca+Aa×Bca Aca×Ba+(1-Aa)×Bca (1-Aa)×Bca (1-Ba)×Aca Bca×Aa Aca×Ba Bca+(1-Ba)×Aca Aca+(1-Aa)×Bca Bca Aca 0 Blend mode GL_ONE_MINUS_SRC_ALPHA GL_DST_ALPHA GL_ONE_MINUS_SRC_ALPHA GL_ONE_MINUS_SRC_ALPHA GL_ZERO GL_SRC_ALPHA GL_ZERO GL_ONE GL_ONE_MINUS_SRC_ALPHA GL_ONE GL_ZERO GL_ZERO dstFactor Clear Xor Dst-atop Src-atop Dst-out Src-out Dst-In Src-In Dst-Over Src-Over Dst Src Operation

Hardware Blending supports all Porter-Duff Blend Modes ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Additional Blend Modes ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Multi-sample 8x Smoother appearance

Multi-sample Coverage Positions 4x jittered 1x (aliased) 8x jittered 4x orthogonal

Requesting Multisampling in GLUT ,[object Object],[object Object],Aliased 8x multisampling

Color Perception ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Adding Light Energy ,[object Object],[object Object]

Subtractive Color ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Trichromatic Biological Basis ,[object Object]

Color Blindness ,[object Object],Top : 25, 45, 8 Bottom : 6, 56

Tristimulus Values ,[object Object],[object Object],[object Object],C(  ) T 1 , T 2 , T 3 cones optic nerve

Implications of Three Color Theory ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Limitations on Color Reproduction ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Tristimulus Coordinates For any set of primaries, define Note

Maxwell Triangle ,[object Object],Project onto 2D: chromaticity space 1 1 T 1 + T 2 +T 3 =1 1 color solid t 1 t 2 1 1 t 1 + t 2 =1 possible colors

NTSC RGB Maxwell Triangle 1 1 r g r+g+b=1 r+g=1

Producing Other Colors ,[object Object],[object Object],[object Object],[object Object]

XYZ Color Space ,[object Object],[object Object],[object Object],[object Object]

Real Color Spaces ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Color Gamuts spectral colors printer colors CRT colors 350 nm 750 nm 600 nm producible color on CRT but not on printer producible color on both CRT and printer unproducible color

YIQ Color Space for TV ,[object Object],[object Object],[object Object],[object Object],[object Object]

Intuitive Color Spaces ,[object Object],[object Object],[object Object],Hue 3D space for HSL HSV – Hue, Saturation, Value color picker

Gamma Correction ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Non-linear Color Display Issues ,[object Object],[object Object],Conventional rendering (uncorrected color) Gamma correct (sRGB rendered) Softer and more natural Unnaturally deep facial shadows NVIDIA’s Adriana GeForce 8 Launch Demo

What is sRGB? ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],sRGB chromaticity

So why sRGB? Standard Windows Display is Not Gamma Corrected ,[object Object],[object Object],“ Expected” appearance of Windows desktop & icons but 3D lighting too dark Wash-ed out desktop appearance if color response was linear but 3D lighting is reasonable Gamma 1.0 Gamma 2.2 linear color response

Relevance to Graphics ,[object Object],[object Object],[object Object],[object Object],[object Object]

Key Color Observations ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Next Lecture ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

CS 354 Understanding Color

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