AV_report - City University of Hong Kong Department of...

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Unformatted text preview: City University of Hong Kong Department of Electronic Engineering 2010 JPEG based encoder and decode design EE4115 Audiovisual Engineering WANG Xian (50914033) WANG Dian (50947212) I Abstract There are many applications requiring image compression, such as multimedia, internet, satellite imaging, remote sensing, and preservation of art work, etc. Decades of research in this area has produced a number of image compression algorithms. Among those algorithms, JPEG is one of the most popular lossy compression methods. In this project the basic knowledge of JPEG was studied which includes the whole process of compression. With the aid of C language programming, the method was implemented. Quantization table is one of the critical factors in compression. Different methods to generate quantization table were discussed and one of them was used for program implementation. Besides, DCT, zig-zag scanning, run-length coding, Huffman coding, DPCM and data stream construction were all realized by the program. After all of these processes, JPEG bit data stream has been obtained. The program we proposed also provides decoding process which converts the constructed bit data stream back to bit-map file and save it. Furthermore, in this project, different quantization tables were generated sequentially by applying μ-law algorithm. The resulted data compression ratio, PSNR and average bits per pixel (Entropy) were also analysis in regards with two different pictures: Lena and Peppers. It was found that at around average bits per pixel=1 the best compromise can be achieved between compression ration and PSNR. Lastly, DCT errors and another quantization method were further discussed. II Table of Contents Abstract .......................................................................................................................... I 1. Introduction ................................................................................................................ 1 2. Background and methodology ................................................................................... 2 2.1JPEG ................................................................................................................................. 2 2.2Discrete cosine transform ................................................................................................. 3 2.3 Quantization .................................................................................................................... 5 2.4 μ-law ................................................................................................................................ 5 2.5 Zig-Zag scanning ............................................................................................................. 6 2.6 DC and AC stream .......................................................................................................... 7 2.7 Huffman coding and run-length coding........................................................................... 7 2....
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This note was uploaded on 01/11/2011 for the course EE 4115 taught by Professor Waimingtsang during the Spring '10 term at City University of Hong Kong.

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AV_report - City University of Hong Kong Department of...

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