Methods and apparatus for improving picture quality in reduced resolution video decoders

Abstract

Methods and apparatus for improving the quality of images generated by reduced resolution video decoders and new and improved video decoders which produce reduced resolution images are described. Methods and apparatus for identifying conditions within an image which may significantly degrade image quality if particular portions of the image are used by a reduced resolution decoder as reference data are described. In particular, 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. Identified constant block areas found in multiple frames are decoded at even lower resolution than other image areas. 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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