H.263 中预先判别全零系数的新方法

New Early Detection Method of All Zero Coefficients in H.263

用Ｈ．２６３标准对低码率图象编码时，由于预测较准确，经过帧间预测后得到的运动补偿数据通常很小，对这种数据块再进行离散余弦变换和量化后往往成为全零块．为减少编码器的运算量，提出了一种预先判断全零系数块的新方法，它以运动估计所得各块的最小绝对误差和为判断准则，不需要附加别的运算．将本方法应用于Ｈ．２６３中，对ＭｉｓｓＡｍｅｒｉｃａｎ和Ｃｌａｉｒｅ图象序列进行实验，发现有４０％以上的块可以在做离散余弦变换和量化前被判别为全零系数块．该方法较大幅度地减少编码器的运算量，对于Ｈ．２６３软件实时实现非常有意义．这种方法可以随量化级的变化自适应地调整全零块的判断阈值．另外，因为该方法采用的判据为全零块的充分条件，所以它不会因为误判而影响解码后的图象质量．

The value of motion compensation data usually is very low.After DCT and quantizing,these data often become all zero.In order to reduce the computation, a new method is proposed in this paper by which the blocks whose quantized DCT coefficients are completely zero can be pre determined. As SAD(sum of minimum absolute difference) resulted from motion estimation are used as criteria, no additional computation is needed. Using this method in H.263,above 40% blocks of Miss America and Claire sequences can be determined to be all zero coefficients before doing the DCT and quantizing. It can greatly reduce the computation, therefore it is very useful to the software implementation of H.263 in real time. In this method, the threshold can be changed with the quantiation level.And with the good criteria,the decoded image is not distorted by incorrect determination.