CS 354 Blending, Compositing, Anti-aliasing
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The document summarizes a lecture on blending, compositing, and anti-aliasing in computer graphics. It discusses how colors are combined during rendering using blending operations, and how compositing operates on entire images rather than individual pixels. Porter-Duff models for digital image compositing are explained, along with how they relate to OpenGL blending functions.
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CS 354 Blending, Compositing, Anti-aliasing
- 1. CS 354 Blending, Compositing, Anti-aliasing Mark Kilgard University of Texas February 14, 2012
- 13. A Simplified Graphics Pipeline Application Vertex batching & assembly Triangle assembly Triangle clipping Triangle rasterization Fragment shading Depth testing Color update/blending Application- OpenGL API boundary Framebuffer NDC to window space Depth buffer Re-examine framebuffer color update…
- 14. A few more steps expanded Application Vertex batching & assembly Lighting View frustum clipping Triangle rasterization Fragment shading Depth testing Color update/blending Application- OpenGL API boundary Framebuffer NDC to window space Depth buffer Vertex transformation User defined clipping Back face culling Perspective divide Triangle assembly Texture coordinate generation
- 16. Blending Enabled vs. Disabled pixel color fragment color blend operation pixel color fragment color glDisable ( GL_BLEND ) glEnable ( GL_BLEND )
- 19. Why blending? compositing window systems volumetric effects; explosions medical imaging compositing complex art work
- 20. Conventional Blend Operation source color destination factor destination color source factor × × + clamp [0,1] pixel color fragment color
- 21. Conventional Blend Operation source color destination factor destination color source factor × × + clamp [0,1] pixel color fragment color × × × + + + × × × clamp [0,1] clamp [0,1] clamp [0,1] modulate, add, and clamp operations are vector on RGBA components
- 22. Conventional Blend Operation source color destination factor destination color source factor × × + clamp [0,1] pixel color fragment color glBlendFunc ( srcFunc , dstFunc )
- 23. Blend Function Parameters where s = min(A s ,1-A d ) (s,s,s,s) GL_SRC_ALPHA_SATURATE (1-A c ,1-A c ,1-A c ,1-A c ) GL_ONE_MINUS_CONSTANT_ALPHA (A c ,A c ,A c ,A c ) GL_CONSTANT_ALPHA (1-R c ,1-G c ,1-B c ,1-A c ) GL_ONE_MINUS_CONSTANT_COLOR (R c ,G c ,B c ,A c ) GL_CONSTANT_COLOR (1-A d ,1-A d ,1-A d ,1-A d ) GL_ONE_MINUS_DST_ALPHA (A d ,A d ,A d ,A d ) GL_DST_ALPHA (1-A s ,1-A s ,1-A s ,1-A s ) GL_ONE_MINUS_SRC_ALPHA (A s ,A s ,A s ,A s ) GL_SRC_ALPHA (1-R d ,1-G d ,1-B d ,1-A d ) GL_ONE_MINUS_DST_COLOR (R d ,G d ,B d ,A d ) GL_DST_COLOR (1-R s ,1-G s ,1-B s ,1-A s ) GL_ONE_MINUS_SRC_COLOR (R s ,G s ,B s ,A s ) GL_SRC_COLOR (1,1,1,1) GL_ONE (0,0,0,0) GL_ZERO ( f r , f g , f b , f a ) Parameter
- 31. Blend Color for Factors source color destination factor destination color source factor × × + clamp [0,1] pixel color fragment color glBlendColor (r,g,b,a) blend color
- 32. Min/Max Blend Operation source color destination color min or max clamp [0,1] pixel color fragment color glBlendEquation ( GL_MIN ) glBlendEquation ( GL_MAX )
- 36. Properly Ordered Compositing vs. Incorrectly Ordered
- 37. Properly Ordered Compositing vs. Incorrectly Ordered
- 42. 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
- 43. 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
- 44. 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
- 48. Multi-sample 8x Smoother appearance
- 49. Multi-sample Coverage Positions 4x jittered 1x (aliased) 8x jittered 4x orthogonal