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Lab9 Case Study

Lab9 Case Study. Speaker: Yu-Lin Hsiao Advisor: Prof. Chun-Yao Wang December 1, 2005. Department of Computer Science National Tsing Hua University. Outline. JPEG Baseline Compression Lab requirement & report. JPEG Baseline Compression. Baseline Sequential DCT-based coding

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Lab9 Case Study

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  1. Lab9 Case Study Speaker: Yu-Lin Hsiao Advisor: Prof. Chun-Yao Wang December 1, 2005 Department of Computer Science National Tsing Hua University

  2. Outline • JPEG Baseline Compression • Lab requirement & report

  3. JPEG Baseline Compression • Baseline Sequential DCT-based coding - Lossy Compression • Content ﹣RGB → YUV ﹣Sub-sampling ﹣Shift the block ﹣FDCT ﹣Quantize ﹣Zig-Zag Scan ﹣Entropy Coding

  4. JPEG Encoder Overview • Split into 8×8 pixels per block • Use FDCT, Quantizer and Entropy encoder to compress data

  5. RGB → YUV (1) • RGB format ﹣Three data segments per pixel, each segment consists 8 bits. ﹣255, 0, 0 → pure red • YUV format • Y：Luminance • U：Cb, Blue Chrominance • V：Cr, Red Chrominance

  6. RGB → YUV (2) • Y = 0.299 R + 0.578 G + 0.114 B • U = – 0.1687 R – 0.3313 G + 0.5 B + 128 • V = 0.5 R – 0.4187 G – 0.0813 B + 128

  7. Sub-sampling • Discarding of chrominance data • YUV can be sub-sampled as 4:2:2 or 4:1:1 ratio

  8. Shift the block • The block is shifted from 0 ~ 255 to -128 ~ 127 by subtracting 128

  9. DC coefficient FDCT (Forward Discrete Cosine Transform) • Spatial domain → frequency-space

  10. Quantize the block • Formula： (Round to nearest integer) Quantized value (a, b) = DCT (a, b) / Quantization Table value (a, b)

  11. Zig-Zag Scan

  12. Entropy Coding • Entropy Coding : develop "code" words for the input value or " symbols“. • Entropy coding transfer the quantized data to compressed data • Entropy coding is composed of Run Length Coding (RLC) and Variable Length Coding (VLC, Huffman Coding)

  13. AC Run Length Coding • Zero is the value occurs at highest frequency in quantized data

  14. Variable Length Coding (DC Huffman Coding) • DC code word = Category code word + DIFF code word

  15. Variable Length Coding (AC Huffman Coding) • AC code word = Run-Size code word + AC coefficient code word

  16. Outline • JPEG Baseline Compression • Lab requirement & report

  17. Requirement • Try to explain the given DCT content • Implement the JPEG encoder (We will give you fully C or C++ code, you can modify the reference code) • Compare the timing constraint of your own design with the reference code (profiling)

  18. HW/SW Implementation • Partition your design into HW & SW parts and implement it

  19. Report • Source code of your JPEG encoder • Profiling file of your source encoder • Report that describes your idea and result (or differences) • Determine the HW/SW part

  20. Reference • JPEG Baseline Compression • Code Example supplied by NCTU • JPEG Still Image Specification • Lab08：How to design an IP with AMBA standard

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