| 摘要 |
A video decoder capable of downsampling full resolution images on a block by block basis regardless of the downsampling rate is disclosed. When the applied downsampling rate does not divide evenly into the number of pixel values included in a block in the dimension being downsampled, the decoder generates a partial pixel value. A partial pixel value represents a portion of the information used to represent a pixel of an image. In contrast, a full or complete pixel value is a value represents all the information used to represent a pixel of an image. The generated partial pixel value is stored and then added to another partial pixel value generated by downsampling another block of pixel values corresponding to a portion of a full resolution image. Numerous drift reduction processing techniques applicable to downsampling decoders are disclosed. Many of these processing techniques are applicable to decoders which perform full order IDCTs as well as reduced order IDCTs. In one embodiment, spatial filtering is applied to anchor frames as part of the motion compensation process in order to reduce or eliminate drift. The spatial filtering is performed as a function of the location of the current block being decoded, the location within the anchor frame of the data being used for prediction purposes, and the motion vector being applied. Various drift reduction techniques applicable to interlaced and non-interlaced images are also described with drift reduction processing for interlaced images being applied differently than for non-interlaced images. In order to maximize the benefit from limited drift reduction processing resources, in various embodiments the amount of drift reduction processing is varied depending on the type of data being processed, e.g., more drift reduction processing is performed on uni-directionally encoded blocks than bi-directionally encoded blocks.
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