MPEG-4 Part 2, VisualTTransform module:contraintsThe data within the transformdomain should be Non-correlated (decorrelated):separated into components with minimalinter-dependency Compact:data energy must be concentrated in a small number of values(coefficients) Thetransform shouldbe reversible The transform should bereasonable from the computation p.o.v.Block-based(Karhunen-Loeve,SvD,DCT)/image-based(DWT)
Transform module: contraints MPEG-4 Part 2, Visual The data within the transform domain should be Non-correlated (decorrelated): separated into components with minimal inter-dependency Compact: data energy must be concentrated in a small number of values (coefficients) Block-based (Karhunen-Loeve, SVD, DCT) / image-based (DWT) The transform should be reversible The transform should be reasonable from the computation p.o.v
MPEG-4 Part 2,VisuaTTransform module:DCTJBlock-basedtransformY = AXA!X=AYAInversetransform:Directtransform:(2j+1)i元A., = C, cos2N2.,(i>0)
Transform module: DCT MPEG-4 Part 2, Visual T Y AXA = Block-based transform Direct transform: T Inverse transform: X A YA = (2 1) cos 2 ij i j i A C N + π = 1 ,( 0) 2 ,( 0) i i C i N C i N = = = >
MPEG-4Part2.VisualTTransform module:DCT Examplefora4x4block1cOs(O)cos(O)cOs(O)cOS(O)222212-21元-83元5元1元S8288LZ112i22元0元41OS12889113元1cos(6COSCOS002
Transform module: DCT MPEG-4 Part 2, Visual Example for a 4x4 block 1 1 1 1 cos(0) cos(0) cos(0) cos(0) 2 2 2 2 1 1 3 1 5 1 7 cos( ) cos( ) cos( ) cos( ) 2 8 2 8 2 8 2 8 1 2 1 6 1 10 1 14 cos( ) cos( ) cos( ) cos( ) 2 8 2 8 2 8 2 8 1 3 1 9 1 15 1 21 cos( ) cos( ) cos( ) cos( ) 2 8 2 8 2 8 2 8 A π π π π π π π π π π π π =
MPEG-4 Part 2, VisualTTransform module:DCT Examplefora4x4block0.50.50.50.50.271-0.6530.6530.271A=0.5-0.5-0.50.50.271-0.653-0.6530.271
Transform module: DCT MPEG-4 Part 2, Visual Example for a 4x4 block 0.5 0.5 0.5 0.5 0.653 0.271 0.271 0.653 0.5 0.5 0.5 0.5 0.271 0.653 0.653 0.271 A − = − − − −
MPEG-4 Part 2, VisualTTransform module:DCT Basicelement:the8x8pixelsblock4-12bits/pixelNewLuma &chromavalues forthe MBs belongingtoI-frames,prediction errorforMBswithinPandB-frames
Transform module: DCT MPEG-4 Part 2, Visual Basic element: the 8x8 pixels block Luma & chroma values for the MBs belonging to I-frames, prediction error for MBs within P and B -frames 4-12 bits / pixel New