Bitrate reduction techniques for image transcoding

Abstract

This disclosure describes techniques for encoding data to compress image data to a reduced size. The techniques may be particularly effective in transcoding an image to a reduced size for transmission. An encoding device may transcode an image to an acceptable file size using bitrate control techniques that affect the entire image uniformly to transcode the image. For example, the encoding devicemay modify one or more quantization tables as a function of the near linear relationship between bitrate (R) and the number of zero-valued quantized transform coefficients to reduce the file size uniformly over the entire image. Alternatively, or additionally, the encoding device may transcode the image using bitrate control techniques that affect only specific localized regions of the image.

Description

[0001] This application claims the benefit of US Provisional Application No. 60 / 941,041, filed May 31, 2007, which is hereby incorporated by reference in its entirety. technical field [0002] The present invention relates to compression, and in particular to the compression of images. Background technique [0003] Compressing images into image files for transmission and storage has become necessary in many different applications including Internet image transmission, digital imaging, image messaging, and the like. Image compression techniques such as Joint Photographic Experts Group (JPEG) may allow high resolution images to be stored in relatively small image files. With the convergence of digital cameras and wireless communication devices, these image files can now be shared via wireless networks. However, this sharing can be expensive in terms of network resources such as time and bandwidth. In order to reduce or limit these costs, wireless network providers sometimes ...

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Problems solved by technology

However, this sharing can be expensive in terms of network resources such as time and bandwidth

To reduce or limit these costs, wireless network providers sometimes impose file size limits on the image files that can be transferred over the network

To comply with these file size restrictions, compressing the image to the imposed file size limit may result in a significant loss of image quality

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