基于输入图像内容的比特率控制

在静止图像的压缩中 ,为得到固定大小的码流文件 ,有必要根据输入图像的特点 ,自适应地控制量化器的参数 ,从而控制输出压缩图像的比特率 .JPEG标准未给出比特率控制方法 ,而一些传统的比特率控制方法为专用的压缩解压缩系统设计 ,并不适用在于开放的基于交换格式的 JPEG压缩系统 .本文提出一种和 JPEG标准完全兼容的比特率控制算法 ,按照输入图像的活动性 ,计算相应的压缩质量因子 ,自适应地为每个 8× 8的块分配比特数 ,并且在熵编码时调整各块的比特数 ,适时启动块截除 ,保证压缩文件的大小不超过预先给定值 .本算法适用于存储容量有限的静止图像压缩的场合 ,可以保证存储规定帧数的压缩文件图像

A Bit-Rate Control Algorithm Based on the Input Image Content

To output fixed size compressed code stream file, it's necessary to control the bit rate by adaptively adjusting the quantization parameter. There's no BRC(bit rate control)method given in JPEG standard, and the traditional BRC is not appropriate for JPEG exchange format .In this paper, we propose a BRC compatible to JPEG exchange format, the activity level of the input image is calculated after DCT, and the quality factor for the required bit rate is determined. With bit allocation, block truncation and bit adjustment, the file size is guaranteed to be no more than the given size. The algorithm is useful for still image compression when the capacity of the memory is limited and fixed number of compressed files is required.