| 摘要 |
Some embodiments of the invention provide a method for specifying a bit allocation for encoding a set of images in a sequence of video images. The method computes a masking value for one or more images. The method computes a bit allocation for a current image based on the computed masking value of one or more images. In some embodiments, the method further ascertains a total number of bits used for images that have been already encoded before computing the bit allocation. The computed bit allocation for the current image is also based on the total number of bits used in some embodiments of the invention. In some embodiments, the method specifies a bit allocation for the current image by specifying a quantization parameter (QP) value for the current image. The method then adjusts the specified QP value based on a categorization of the current image. Examples of such categorizations include: (1) category 1 images, which are images at natural scene changes or images that collectively capture a fast motion, (2) category 2 images, which are imaged forced to be intrablock encoded and are not category 1 images, (3) category 3 images, which are images that should be easy to encode, (4) category 4 images, which are images at the transition between simple and difficult images, and (5) category 5 images, which are images that do not fall in the other categories. In some embodiments, the sequence of frames is divided into a set of blocks, where each block has (1) a size and (2) a bit allocation. Some embodiments dynamically adjust the size of the blocks during the encoding operation. In some embodiments, unused bits allocated to a first block are rolled over to a second block. In other embodiments, only some of the unused bits are rolled over to the second block.
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