Frame compression using radix approximation or differential code and escape code

Abstract

Digital video data streams that conform to standards such as the ITU-T H.263 and MPEG-4 ISO / IEC standards are compressed to reduce the amount of memory needed to store these streams. In a technic, information for a sequence of frames is compressed by rounding and truncating luminance values, and by encoding chrominance values using a radix tree and a palette. Each entry in the palette stores information representing a color that actually occurs at least once in the sequence of frames. The radix tree provides an efficient way to generate compressed representations for colors that are stored in the palette, and also provides a way to identify the color in the palette that is the closest match to other colors in the data stream that are not stored in the palette. In another technic, information for groups of pixels are compressed into segments of encoded information. Each segment of encoded information includes luminance values that are rounded and truncated, the full-length values of chrominance information for the first pixel in the group, and codes that represent differences in chrominance values between adjacent pixels in the remainder of the group. A special 'escape' code is used to represent the chrominance value for a pixel whenever the difference in chrominance values between that pixel and the preceding pixel exceeds a threshold.

Description

technical field

[0001] The present invention relates generally to video signal processing, and more particularly to reducing the amount of storage required to process encoded digital video data streams compliant with ITU-T H.263 and MPEG-4 ISO / IEC standards. Background technique

[0002] Memory is expensive, and most of the storage space required to process an encoded digital video data stream is used to store the luminance and chrominance values ​​for each pixel in a frame of data. As a frame is decoded and processed, information about the frame must be stored in memory. While reducing memory requirements is attractive for any application, it is particularly important for applications in handheld and low-power devices such as mobile phones and so-called Personal Digital Assistants (PDAs), where limited board space and power are critical. The size and power requirements of the memory chip are limited.

[0003] Many applications conform to one of two encoding standards that...

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