高质量图象压缩的自适应DPCM/DCT混合编码方法

AN ADAPTIVE HYBRID DPCM/DCT CODING METHOD FOR HIGH QUALITY IMAGE COMPRESSION

DCT是数据压缩的主要技术之一 ,它能将图象的主要能量集中在很少的几个 DCT系数上 .可是 ,DCT对于含有较多边缘的图象块并不十分有效 ,因为 DCT变换作用于这样的图象块后不能导致有效的能量集中 .文中提出了一种自适应 DPCM/ DCT混和编码方法用于解决这一问题 .对于每一个图象块 ,边缘检测器自动判断该块是否含有较强的边缘 ,如果含有较强的边缘 ,则使用DPCM编码器 ;如果不含有较强的边缘 ,则使用 DCT编码器 .DPCM编码器自动从给定的预测器中选定一个产生最小预测误差的预测器 ,然后用 Rice编码器对误差图象编码 .对于非边缘块 ,使用DCT、游程和变长编码技术 .实验结果显示文中所提出的方法在压缩比和解码时间方面优于 JPEG无失真模式和标准 JPEG模式 (当 bpp=1— 4时 )

Discrete cosine transform(DCT) is one of the key techniques in data compression. DCT can compact the most image energy into only a few of the DCT coefficients. This method is, however, not suitable for the blocks with some edges contained. Transformation of such an edge block will not lead to an efficient energy compaction. An adaptive hybrid DPCM/DCT coding method is proposed for solving this problem. For each incoming block, edge detector switches to the DPCM coder if this block contains sharp edges,and if not it switches to the DCT coder. The DPCM coder adaptively selects from the given set a predictor that results in a minimum prediction error, and then the residuals obtained is encoded with Rice coder. For non\|edge blocks, DCT, run\|length and variable length coding are applied. Experiments show that the proposed method is better than JPEG lossless mode and baseline JPEG performance both on compression ratio and on decoding run\|time when bpp=1—4 approximately.