| 摘要 |
Regions of a source image (900) are encoded at different levels of image quality. A plurality of image quality levels are defined (1010). In addition, the source image (900) is divided into one or more regions (912, 914, 916) and one of the image quality levels is assigned to each region (1012). Next, the entire source image (900) is encoded, preferably with JPEG encoding, at the lowest image quality level Q1, assigned to the image (1016). Then, the encoded source image (900) is decoded by a matching decoding process into a reference frame (1018). If the next highest image quality level Q2 is lossy, then the reference frame and source image are scaled according to the image quality level Q2 (1020). Then, differences between the source image and the reference frame are determined for all lossy regions assigned an image quality level greater than or equal to the image quality level Q2, and stored in a differential frame (1024). The differential frame is encoded according to the image quality level Q2 (1026), stored with the reference frame, then decoded to become the new reference frame (1028). These steps are repeated until the highest quality level assigned to a region is encoded. If the image quality level is lossless, then the reference frame is scaled to the resolution of the source image (1030), and the differential components are losslessy encoded (1038). When the variably encoded image is decoded, each of the selected regions (912, 914, 916) has the image quality defined by the assigned image quality level.
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