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An Empirical Analysis of Requantization Errors for Recompressed JPEG Images

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Author(s): B.VINOTH KUMAR | Dr.G.R.KARPAGAM

Journal: International Journal of Engineering Science and Technology
ISSN 0975-5462

Volume: 3;
Issue: 12;
Start page: 8519;
Date: 2011;
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Keywords: JPEG | Image Compression | Quantization | Recompression | Requantization Error | Rounding Technique.

ABSTRACT
Images from sources like digital camera, internet and the like are in the JPEG format. There is a tremendous need for recompression of JPEG images in order to satisfy the space constraints and to transmit the images with limited bandwidth. Several techniques have been developed for recompressing the JPEG image in order to achieve low bit rate and to have good visual quality. In this paper, we concentrated on requantization method to achieve recompression. We have analyzed the occurrence of requantization errors empirically for Normal rounding technique. Based on our experience, we have proposed the Enhanced rounding technique for requantization of JPEG images. The resulting images are generally smaller in size and have improved perceptualimage quality over Normal rounding technique. We have compared the recompression results for standard benchmark 256x256 gray scale images against image quality measures such as image size, compression ratio,bits per pixel and Peak Signal to Noise Ratio (PSNR).
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