Characterizing the effect of spatial translations on JPEG-compressed images

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Title: Characterizing the effect of spatial translations on JPEG-compressed images
Author: Jacoby, Keith
Abstract: The JPEG Still Image Data Compression Standard is one of the most pervasive digital image compression schemes in use today. JPEG is especially suited to digitized photograph archiving, and lately has grown popular in industry as a standard for handling images on networks and the Internet. The emergence of new applications and image file formats (FlashPix) that use JPEG compression is allowing developers and software users to create applications that retrieve, manipulate, and store images in databases located on the Internet. In most cases, these applications are dealing with JPEG images, or a format that uses JPEG as the compression scheme, as is the case with the FlashPix format. Some of these new applications are allowing clients (web users) to enhance and manipulate these downloaded images, and then restore them on these image repository databases. Unfortunately, with JPEG compression, there is a cost that comes with compression and decompression. Blocking artifacts will always result when using JPEG to compress images, and the artifacts become worse with lower quality levels of compression, or higher compression ratios. These artifacts usually are acceptable if a little care is taken in choosing the quality factor, however, other degradation occurs whenever an image is translated, or shifted by a few pixels, in a horizontal or vertical direction. Translation can happen very easily if the image is cropped or otherwise moved. When such an image is recompressed, additional error can cause substantial artifacts that would be absent if the image was not moved. If the JPEG scheme could be modified to recognize the translations by compensating for the crop or translation, the artifacts due to this translation would be eliminated. The proposed research will attempt to characterize the error that results from such translations.
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Date: 1998-05

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