图象块编码—分类的方法

A Method of Image Classified Block Coding

提出了一个基于ＤＣＴ和二维多项式近似的块分类编码算法。在该算法中，原始图象被分割成互不覆盖的８×８子块。通过依次地利用灰度局部方差、二维多项式近似误差和图象信号的空间频率分布，把图象块分为均匀、平滑、粗糙和细节４类。均匀块和平滑块分别采用零阶和一阶多项式近似。粗糙和细节块先进行ＤＣＴ变换，然后对其ＤＣＴ系数量化后采用改进的游程编码表示。实验结果表明该算法具有良好的性能。在未采用熵编码为编码码流作后处理的情况下，性能仍优于ＪＰＥＧ标准。

Classified Block Coding has received more attention recently for the advantage of easy implementation. The classification and coding of blocks are the two important problems in classified block coding.In this paper, we propose a classified block coding algorithm based on DCT coding and polynomial approximation. In the algorithm, the original image is splitted into nonoverlapped 8×8 blocks. The blocks are classified into four classes: constant blocks, smooth blocks, coarse blocks and detail blocks, by using the intensity local variance, the polynomial approximation error and spatialfrequency distribution. The constant blocks and smooth blocks are approximated by 0order and 1order polynomial respectively. For the coarse and detail blocks, we compute and quantize their DCT coefficients. Then encode them by means of an improved runlength coding. The experiment results show that the proposed algorithm, without using entropy coder as postprocessor of the codes, has better performance than JPEG.