| 摘要 |
Disclosed is an image encoder that divides a digital image into a set of“macroblocks.”If appropriate, a macroblock is“downsampled”to a lower resolution. The lower-resolution macroblock is then encoded by applying spatial (and possibly temporal) prediction. The“residual”of the macroblock is calculated as the difference between the predicted and actual contents of the macroblock. The low-resolution residual is then either transmitted to an image decoder or stored for later use. In some embodiments, the encoder calculates the rate-distortion costs of encoding the original-resolution macroblock and the lower-resolution macroblock and then only encodes the lower-resolution macroblock if its cost is lower. When a decoder receives a lower-resolution residual, it recovers the lower-resolution macroblock using standard prediction techniques. Then, the macroblock is“upsampled”to its original resolution by interpolating the values left out by the encoder. The macroblocks are then joined to form the original digital image.
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