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Abstract

Techniques for identifying blocks of pixels, referred to as constant block regions, having approximately the same intensity in terms of luminance values, are discussed. High contrast vertical and/or horizontal edges will cause significant prediction errors in images generated by reduced resolution decoders under certain conditions. Methods for assessing when such conditions exist and a significant prediction error is likely to occur are described. In addition methods and apparatus for minimizing the effect of such prediction errors in downsampling decoders are also described. One specific embodiment is directed to a new video decoder which decodes portions of a single image, e.g., frame, at different resolutions. Areas of the image along high contrast vertical or horizontal edges are decoded at full resolution while other portions of the same image are decoded at reduced resolution. By decoding and storing portions of reduced resolution images at full resolution for reference purposes, the risk of prediction errors resulting from the use of downsampling on reference frames is reduced.

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First Claim