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11110

YUV RGB. DCT. ZZ. Q. VLC. +. in. -. 68. -23. -4. -3. 11110. 68. 70. 7. 0. 0. 0. 8. -23. -28. 17. 3. 101. -20. -23. -2. Non-overlapping 8x8 blocks. 0. 0. 8. 8. sym. code. -4. 17. 20. -11. 101. -23. -20. -2. 0. 0. 0. 8. 8. 4. -3. 3. -11. -12. 0.

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11110

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  1. YUV RGB DCT ZZ Q VLC + in - 68 -23 -4 -3 11110 68 70 7 0 0 0 8 -23 -28 17 3 101 -20 -23 -2 Non-overlapping 8x8 blocks 0 0 8 8 sym code -4 17 20 -11 101 -23 -20 -2 0 0 0 8 8 4 -3 3 -11 -12 0 -4 0 0 -1 100 8 8 4 4 -2 101 11100 -3 -28 -30 +2 110 0 -4 0 0 2 0 0 9 70 -20 0 0 -3 11100 0 0 0 -3 +1 11101 0 0 7 8 -20 -30 20 0 +7 11110 110 17 2 20 0 7 8 4 0 20 20 -10 110 20 2 17 9 8 4 3 0 0 -10 -10 0 0 0 -3 0 3 0 0 110 20 20 2 0 0 0 3 offset 100 -10 -11 -1 - 100 -10 -1 -11 IDCT ZZ IQ VLD + 100 -12 -10 -1 out JPEG Joint Photographic Expert Group jvm

  2. Coding principle: frequent data words have shorter code words than infrequent data words Decoding (throughput) problem: “hidden” code word boundaries -> algorithm comprises a feedback loop Clock cycle Data word bitstream Code book 0 1 2 3 4 5 6 1100111100110 1100111100110 1100111100110 1100111100110 1100111100110 1100111100110 1100111100110 - 10 00 11 01 00 10 Code word Data word probability 0 10 110 111 00 01 10 11 50% 25% 12.5% 12.5% Average length 1.75 bits 2 bits 1/2+2/4+3/8+3/8 jvm

  3. Multiple components, interleaving and minimum coded unit A1 A2 B1 B2 C1 C2 An Bn Cn non-interleaved MCU = 1 data unit = 8x8 pixels A1 A2 B1 B2 C1 C2 … An … Bn … Cn scan1 scan2 scan3 MCU interleaved MCU=3 data units A1 B1 C1 A2 B2 C2 … An Cn Bn scan1 jvm

  4. Multiple components with different dimensions A1 A2 B1 B2 C1 C2 An Bn/2 Cn/2 MCU interleaved MCU=4 data units A1 A2 B1 C1 A3 A4 B2 C2 … An-1 An Cn/2 Bn/2 scan1 jvm

  5. X : number of horizontal samples in image Y : number of vertical samples in image xi : number of horizontal samples in component Ci yi : number of vertical samples in component Ci C4 xi = ceil(X*Hi/Hmax) yi = ceil(Y*Vi/Vmax) C3 C2 C1 Example: X=Y=512 Hmax=4 Vmax=2 C1 H1=4 V1=1 x1=512 y1=256 C2 H2=2 V2=2 x2=256 y2=512 C3 H3=1 V3=1 x3=128 y3=256 jvm

  6. SOI APP < ...> DQT <quantisation table 1> DQT <quantisation table 2> SOF <image info, size …> DHT <huffmann table 1> DHT <huffmann table 2> DHT <huffmann table 3> DHT <huffmann table 4> SOS <encoded data> jvm

  7. SOI Frame EOI Quant. Tables Frame header Scan1 Scan2 … Scann SOF DQT Huffmann tables Scan header ECS DHT SOS MCU1 MCU2 ... MCUn jvm

  8. Frame header structure • Parameter size in bits • Marker (FFC0…FFCF) 16 • frame header length 16 • sample precision 8 • number of lines 16 • number of samples/line 16 • number of components in frame 8 • for each frame component • component identifier 8 • horizontal sampling factor 4 • vertical sampling factor 4 • quantization table destination selector 8 jvm

  9. Scan header structure • Parameter size in bits • Marker (FFDA) 16 • scan header length 16 • number of components in scan 8 • for each component • component selector 8 • DC entropy coding table selector 4 • AC entropy coding table selector 4 • start of spectral selection or predictor selection 8 • end of spectral selection 8 • successive approximation bit stream position high 4 • successive approximation bit stream position low 4 jvm

  10. DHT marker segment structure • Parameter size in bits • Marker (FFC4) 16 • Huffman table definition length 16 • for each Huffman table • table class 4 • Huffman table identifier 4 • number of Huffman codes of length i (Li) • for i = 1..16 8 • value associated with each Huffman code • for i = 1..16; j = 1..Li 8 jvm

  11. Table for luminance DC difference (p. 509) 0 00 1 010 2 011 3 100 4 101 5 110 6 1110 7 11110 8 111110 9 1111110 10 11111110 11 111111110 jvm

  12. FF C4 0 1F 0 0 1 5 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 2 3 4 5 6 7 8 9 A B 5 words of length 3 Length = 31 B values 1 words of length 2 Class AC|DC 0 words of length 1 jvm

  13. DQT marker segment structure • Parameter size in bits • Marker (FFDE) 16 • Quantization table definition length 16 • for each Quantization table • Quantization table element precision 4 • Quantization table identifier 4 • Quantization table element (0..63) 8 or 16 jvm

  14. Structure of the Guerrier code jpeg.c jpeg.h utils.c parse.c get_bits ( ) get_next_MK ( ) load_quant_tables ( ) init_MCU ( ) process_MCU ( ) fast_idct.c idct_1d ( ) IDCT ( ) color.c tree_vld.c load_huff_tables ( ) get_symbol ( ) huffman.c unpack _block ( ) spy.c unpack.c jvm

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