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Enhancements for JPEG Compression

Enhancements for JPEG Compression. Bo- Zong Wu ( 吳柏宗 ) Visual Communications Laboratory Department of Communications Engineering National Central University. Goals in this Homework. Run and implement JPEG compression Algorithm. Enhance the performance of JPEG. JPEG Flow Chart.

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Enhancements for JPEG Compression

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  1. Enhancements for JPEG Compression Bo-Zong Wu (吳柏宗) Visual Communications Laboratory Department of Communications Engineering National Central University

  2. Goals in this Homework Run and implement JPEG compression Algorithm. Enhance the performance of JPEG.

  3. JPEG Flow Chart

  4. Drawbacks of JPEG In low bit-rate, blocking effect is easy to observe.

  5. Evaluate Compression Performance – PSNR(1/2) • Higher PSNR represent the • better image quality. I: original image K:reconstruct image MSE : mean square error (get from original image and compressed image.) MAX : in 8 bits image, MAX = 255. • Calculate PSNR of gray image : just calculate PSNR from gray image. • Calculate PSNR of color image: calculate the PSNR of red, green and blue • channels, then calculate the mean of three PSNR.

  6. Evaluate Compression Performance – PSNR(1/2) Red is better because the PSNR is higher than blue in same compression rate. Diagrams of PSNR curve

  7. How can We Improve the Performance JPEG • Goal: • Higher PSNR or good visual quality in same compression ratio. • Higher compression ratio in same PSNR. • Add more functions or improve the performance for some specific image. • Some possible way: • Use different DCT transform. • Reduce block effect. • Design different quantized table. • Other method which you can think….

  8. The Possible Ways to Enhance JPEG • Reduce blocking effect: • Use some pre-process or post-process to reduce the blocking effect. • Find the “edge” between blocks, use the tools which you’ve learned to reduce the blocking effect. • Different DCT transform • Search papers and find different types of DCT, compare your DCT with original DCT in JPEG. • Design quantization table • If you designed better quantization table or other better quantization method, you can get better PSNR or visual quality in same compression ratio.

  9. Useful Sources JPEG home website : http://www.jpeg.org/jpeg/index.html Paper : http://intranet-gei.insa-toulouse.fr/~sicard/cours/mmedia/Chap2.3/wallace.pdf You can find a lot of information about JPEG from Google, or go to library to find some books. We provide an open JPEG source : http://140.115.156.251/vclab/data/course/DIP2009/origin.zip (developed by CristiCuturicu, 1999 ) Standard test images: http://sipi.usc.edu/database/database.cgi?volume=misc

  10. Some Tips • You can implement JPEG codec by yourself, or use our provide JPEG codec. • Be sure your compressed JPEG bit-stream can be opened in windows image viewer or other image viewer like ACDsee. • Must fit in JPEG standard!! • We use standard images(link in p.3) to test the compression performance. The format is TIF, before use our provided codec, you have to transform the format to BMP(使用小畫家就可以了). • If you reference some papers, please add some paper information in your report.

  11. Score • Total score : (10 points) • Report : (2 points) • Program: • Part1 : Run the given JPEG software, can compress BMP to JPEG (1 point) • Part2:Observe the relation between bit-rate(bit per pixel) and PSNR, plot some diagrams of curve. (2 points) • Part3 : Enhance the performance of JPEG (up to 5 points)

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