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CIS679: JPEG (more)

CIS679: JPEG (more). Review of JPEG More about JPEG Lab project. Review of JPEG. JPEG goals Picture Preparation Component, block, and pixel Picture Processing Shift Forward DCT Quantization Different coefficients are treated separately => quantization table. Differential Encoding.

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CIS679: JPEG (more)

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  1. CIS679: JPEG (more) • Review of JPEG • More about JPEG • Lab project

  2. Review of JPEG • JPEG goals • Picture Preparation • Component, block, and pixel • Picture Processing • Shift • Forward DCT • Quantization • Different coefficients are treated separately => quantization table

  3. Differential Encoding • The DC coefficient varies only slowly from one block to the next. • 12, 13, 11, 11, 10, …… • Only the difference in the preceding block is encoded. • 12, 1, -2, 0. –1

  4. Run-length Encoding • The AC coefficients are encoded in the form of a string of pairs of values (skip, value) • (0,6)(0,7)(0,3)(0,3)(0,3)(0,2) (0,2)(0,2)(0,2)(0,0)

  5. Huffman Encoding • Use variable length codes • Most frequently used symbols coded with fewest bits • The intermediate symbol sequence • DC coefficient: (sss, value) • sss: the number of bits needed • Value: the encode value • AC coefficient: (skip, sss) (value) with run-length encoding • skip: the number of consecutive 0 • sss: the number of bits needed to encode the value • Value: the encode value • Huffman code • DC coefficients: 12 = (4, 12) = (1011100) • AC coefficient: (0, 6) = (0, 3) (6) = (100110)

  6. Summary • DC coefficient • Input: 12, 13, 11, 11, 10, …… • Differential encode: 12, 1, -1,-1,-2… • The intermediate symbol sequence: (sss, value) • Huffman code: • P160 (b) => sss • P160 (a) => value • Example: 12 = (4, 12) = (1011100) • AC coefficient • Input: 6,7,3,0,0,3,3,2,0,0,0 • Run-length encoding: (0,6)(0,7)(0,3)(2,3)(0,3)(0,2) (0,0) • The intermediate symbol sequence: (skip, sss) (value) • Huffman code: • P163-164 => (skip, sss) • P160(a) => value • Example: (0, 6) = (0, 3) (6) = (100110)

  7. Lab Project • Objective: be familiar with JPEG • Description • Input: an original 8*8 block => original data (the value of each pixel is in the range of [0,255]) (given by the Instructor) • Steps: • Shifted to the range of [-128, 127] • FDCT (round: 1.6->2, -1.6->-2, 1.5->2, 1.1->1) • Quantized with the given quantization table (see the given example) (round) (round: 1.6->2, -1.6->-2, 1.5->2, 1.1->1) • Zig-zag coded • Converted to the intermediate symbol sequence with run-length encoding on AC coefficients • Encoded to bit sequence with Huffman encoding (based on the given default Huffman codewords tables) => compressed data • The compression ratio = original data size (i.e. 64*8)/compressed data size • Output: print out all the results of the above steps into different files (The names and formats of output files should follow the files put on the web.)

  8. Lab Project • Team: one or 2 students • What should be turned in (via email to chenai@cse.ohio-state.edu, subject: 679 project)? • Put all codes into one file (source_jpeg.c (.cpp) with clear comments (softcopy) • Make sure TA can understand, compile, and run your codes on unix machines. All the codes should be in C or C++. • A report including a summary (2 <= page # <= 5) and the source code file, and result files (hardcopy or softcopy either in PDF) • Due date: Oct. 16, 2006, 5:00pm (EST) (both the code and the report) • How will TA grade? • Correctness: TA will use his own data to test your codes. • Clearness: TA will check whether your code and report are understandable. • Fairness: • Students in the same teams get the same scores. • No copy! All students involved in copy will get ZERO.

  9. Example - Original Block

  10. Example - Shifted Block

  11. Example -After FDCT

  12. Example - Quantization Table

  13. Example - After Quantization

  14. Example – Other Steps Zig-zag sequence 61,-5,6,-2,-5,3,-1,-3,-1,0,0,0,-1,3,3,-1,-1,0,1,1,0,1,0,1,-1,-1,1,-1,-2,1,3,0,0,-1,0,0,0,0,0,-1,0,-1,0,-1,0,1,0,0,0,0,0,0,1,0,1,0,0,0,0,0,0,0,0,0 Intermediate symbol sequence (6)(61),(0,3)(-5),(0,3)(6),(0,2)(-2),(0,3)(-5), (0,2)(3), (0,1)(-1),(0,2)(-3),(0,1)(-1),(3,1)(-1), (0,2)(3), (0,2)(3),(0,1)(-1),(0,1)(-1), (1,1)(1), (0,1)(1),(1,1)(1), (1,1)(1), (0,1)(-1),(0,1)(-1),(0,1)(1),(0,1)(-1),(0,2)(-2),(0,1)(1),(0,2)(3),(2,1)(-1),(5,1)(-1),(1,1)(-1),(1,1)(-1),(1,1)(1),(6,1)(1),(1,1)(1),(0,0) Encoded bit sequence (total 154 bits) (1110)(111101)(100)(010) (100)(110) (01)(01) (100)(010) (01)(11) (00)(0) (01)(11) (01)(00) (00)(0) (111010)(0) (01)(11) (00)(0)(00)(0) (1100)(1) (00)(1) (1100)(1) (00)(0) (00)(0) (00)(1) (00)(0) (01)(01) (00)(1) (01)(11) (11011)(0) (1111010)(0) (1100)(0) (1100)(0) (1100)(1) (1111011)(1) (1100)(1) (1010)

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