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Andrew Puryear PSYCH221/EE362 March 13, 2003

A Study of Possible Improvements in JPEG Compression with Applications in High Compression and Wireless Transmission. Andrew Puryear PSYCH221/EE362 March 13, 2003. http://ise.stanford.edu/~apuryear/. Outline. PART I – COLA-JPEG

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Andrew Puryear PSYCH221/EE362 March 13, 2003

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  1. A Study of Possible Improvements in JPEG Compression with Applications in High Compression and Wireless Transmission Andrew Puryear PSYCH221/EE362 March 13, 2003 http://ise.stanford.edu/~apuryear/

  2. Outline • PART I – COLA-JPEG • The COLA-JPEG is aimed at mitigating the blockiness inherent in the JPEG compression scheme at high compression ratios using a Constant OverLap Add window instead of a rectangular window. • PART II – JPEGa • The JPEGa is aimed at coding an image so that it will be amenable to transmission over hostile wireless channels.

  3. Highly Compressed JPEG • Blockiness visible in the image is a general phenomenon apparent in JPEG images with high compression ratios.

  4. JPEG Compression Process

  5. JPEG Compression Process

  6. JPEG Compression Process

  7. JPEG Compression Process Quantizer: Weights the various spectral coefficients according to their importance, with respect to the human visual system.

  8. COLA-Window • The COLA window is 10-by-10 pixels, maximum of one, first step down 0.75, and second step down of 0.25. • The window has the property that, with a hop size of 8 (in linear combination of horizontal and vertical), it overlaps and adds to a constant value of one.

  9. COLA-Window (Cont.) • COLA Window Pros • Because it is Constant OverLap Add, perfect image reconstruction is possible (with out compression) • Each image block contains part of it’s surrounding blocks… hopefully this will suppress the blockiness • COLA Window Cons • COLA Window is 36% larger than the rectangular window and therefore requires increased quantization for fair comparisons.

  10. COLA-JPEG Comp./Expan.

  11. COLA-JPEG Results – Zero Compression JPEG COLA-JPEG

  12. COLA-JPEG Results –Compression Ratio ~3 JPEG COLA-JPEG

  13. COLA-JPEG Results –Compression Ratio ~9 JPEG COLA-JPEG

  14. COLA-JPEG Results –Compression Ratio ~9 COLA-JPEG

  15. Outline • PART I – COLA-JPEG • The COLA-JPEG is aimed at mitigating the blockiness inherent in the JPEG compression scheme at high compression ratios using a Constant OverLap Add window instead of a rectangular window. • PART II – JPEGa • The JPEGa is aimed at coding an image so that it will be amenable to transmission over hostile wireless channels.

  16. JPEGa – The Wireless Ready JPEG Today’s vision information is increasing being transferred via wireless technologies such as a laptop with a wireless card or a mobile phone with photo-display technology.

  17. JPEGa • The JPEGa ‘standard’ improves the binary encoding step in the JPEG standard to make the image more robust to possible errors during transmission. In this standard, everything is the same as the JPEG except for the Binary Encoder/Decoder.

  18. JPEGa – Convolutional Encoder • The improvement is made by convolutionally encoding the binary sequence. The scheme allows for low bit error rates (BER) even with low signal to noise ratios.

  19. JPEGa – Binary Decoder • The received image is decoded using the so-called Viterbi algorithm. The algorithm looks at the received string (15 bits long in this case) and minimizes the hamming distance between it and all allowed strings of length 15. • More info can be found at: • http://ee.tamu.edu/~ee489/original/MOD_COD.PDF • Page 70.

  20. JPEGa – Performance • To determine the performance of the JPEGa standard, I simulated its transmission trough a wireless channel including the effects of pulse shaping, additive white Gaussian noise, and matched filter detection. • Results are compared with JPEG images transmitted through the same channel.

  21. JPEGa Simulation Details

  22. JPEG Simulation Details

  23. Results 4dB 6dB 8dB 10dB JPEGa JPEG

  24. Conclusions & References Two possible improvements to the JPEG image compression standard have been presented. The first proposed improvement, the COLA-JPEG, was aimed at mitigating the blockiness inherent in the JPEG compression scheme at high compression ratios using a Constant OverLap Add window instead of a rectangular window. This proposed improvement, while being instructive, proved to offer no advantage over JPEG. The second proposed improvement, the JPEGa, was aimed at coding the image so that it would be amenable to transmission over hostile wireless channels. This proposed improvement provides a 4dB gain over the JPEG standard for quality reception at the expense of increased complexity. References: [1] Introduction to JPEG - http://www.faqs.org/faqs/compression-faq/part2/section-6.html [2] Welcome to the JPEG Tutorial! - http://www.ece.purdue.edu/~ace/jpeg-tut/jpegtut1.html [3] B. Wandell, Compression and Multiresolution - http://coursework.stanford.edu/coursework/servlet/ShowFile?contentid=36070 [4] T.S. Rappaport, Wireless Communications - Principles and Practice, 2nd Edition, Prentice Hall, 2001. [5] S. Haykin, Communication Systems. New: Wiley, 2002. [6] G. L. Stüber, Principles of Mobile Communication, 2nd Edition, Kluwer Academic Publishers, 1996.

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