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Compression artifact reduction


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A fast growing archive of JPEG images and short MPEG video clips is generated by digital still cameras. Unfortunately, ringing and blocking artifacts from the block DCT compression may degrade the quality of these images. Reducing these artifacts may improve the display and printing from cell phone camera photos, video clips, images cropped from high-resolution compressed images and images found on the web. Reducing these artifacts also improves the results from subsequently applied algorithms, such as upsampling and color adjustments, that may otherwise accentuate the compression artifacts. Compression artifact reduction also has the potential to improve the millions of images in the accidental archive that the web has become.

A new method, using weighted combinations of shifted transforms, is developed for deringing and deblocking DCT compressed color images. The method shows substantial deringing improvement over prior methods, maintains comparable deblocking and shows comparable PSNR gains. The method automatically adapts to input image quality, and it may be implemented using low-complexity, swath-based processing. Multiplier-less transforms better suited for parallel hardware implementation are developed. Finally, PSNR comparisons are provided for the different methods. The new method using the DCT transform offers good visual results with PSNR comparable to prior work, and the multiplierless transforms offer good visual results at a slight loss in PSNR.

You may view sample images.

Technical details are found in this paper (download available here) :

R. Samadani, A. Sundararajan and A. Said, "Deringing and deblocking DCT compression artifacts with efficient shifted transforms," IEEE International Conference on Image Processing (ICIP), Singapore, October 2004. 


For more information about this technology, please contact Ramin Samadani (Ramin.Samadani @hp.com) at Imaging Technology Dept., HP Labs.

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