Research on Region Adaptive Image Compression Algorithms and Integrated Schemes

主要研究成果如下：(A)研究了一种新的区域自适应分形图像编码方法，该方法将基元块合并成可变大小的范围块。我们取得了以下成果。在原始块的合并过程中，利用块合并引起的总体误差的增加，使信噪比提高了1dB.ii。对于(I)增加门槛不是恒定的，而是先取小值，然后逐渐增加的方案是有效的。当获得按顺序合并的范围块时，以相反的顺序将范围块与周围块重新合并的方案减少了合并顺序的影响。上述(I)-(Iii)方案实现了2dB.V.的压缩性能改进。一种新的可以选择解码迭代次数的分形图像编码方案表明，解码是在一个固定的时间内完成的。(B)对新区域自适应图像压缩的核心--块匹配进行了研究，取得了以下成果。提出了一种减少块间均方误差计算次数的数学算法。它的计算速度大约是传统方案的3倍。此外，搜索顺序的修改和搜索范围的限制导致处理时间减半。(C)在依赖于已编码区域的图像压缩方案中，提出了一种新的方法，即如果由于编码数据的延迟或迭代中断而未完成解码过程，则对数据进行完全解码，并且修改内部缓冲器直到下一区域的解码过程开始。这种方法极大地减少了错误传播。

Main results obtained in the research are listed below.(a) We studied new region adaptive fractal image coding in which primitive blocks are merged into a variable size range block. We have obtained following results.i. In the merging process of primitive blocks, the use of increase of overall error caused by block merging results in the improvement of SN ratio by 1dB.ii. It is effective to the scheme of (i) that the threshold of increase is not constant but firstly small values and increased gradually.iii. The scheme where a range block is re-merged with surrounding blocks in reverse order when a range block merged in an order is obtained reduces influence of merging order.iv. The above schemes of (i) - (iii) achieve the improvement of compression performance by 2dB.v. A new fractal image encoding scheme which can select decoding iteration times shows decoding are finished within a constant time.(b) We studied block matching which is the core of the new region adaptive image compression and obtain following results.i. A mathematical algorithm that reduces calculation times of MSE between two blocks is proposed. It calculates about 3 times faster than the conventional scheme.ii. Moreover, modification of searching order and restriction of searching range result in the half of processing time.(c) In image compression schemes which depend on the region already encoded, a new method is proposed that the data is completely decoded and that the inner buffer is modified until decoding process of the next region starts if decoding process is not completed because of a delay of encoded data or a break of iteration. This method greatly reduces error propagation.