A Research on Fractal Image Coding for Mobile Image Communications

通过本文的研究，取得了以下研究成果：1.在分形图像解码过程中，从理论上研究了由于接收到的压缩数据的错误而导致图像退化的传播机理。我们发现，在编码过程中，无论搜索区域如何，传播误差大约是压缩数据误差的2.4倍。我们提出了一种新的容错编码方法，用与单幅图像相同的数据量发送两次图像。这是通过使用双倍大小的范围块和新的判据来确定域块来实现的。在该方法中，我们根据距离块和定义域块之间的均方误差来确定扩大距离块的最优形状。从编码效率的角度对实验结果进行了验证。并对译码过程中的错误检测机制进行了研究。我们发现，使用阈值的错误检测有时会失败，这阻碍了错误恢复，导致图像质量下降。为了防止错误检测为4，我们在编码器中引入了预处理，它只选择不会导致错误检测的域块。利用基于5的编解码器成功地抑制了误检，验证了该方法在错误信道环境下的峰值信噪比比传统方法有2-3分贝的增益。

Through this research, the following results were obtained :1. In fractal image decoding process, we investigated theoretically the mechanism of the propagation of image degradation caused by errors of received compressed data. We found that the propagated errors are about 2.4 times as the errors of compressed data regardless of the search area in encoding process.2. We proposed a new coding method for error resilience by sending the image twice with the same amount of data as the single image. This is realized by using double-sized range blocks and a new criterion to determine the domain block.3. In the proposed method, we determined the optimal shape of enlarged range blocks from the mean square error between range blocks and domain blocks. We confirmed the results from the viewpoint of the coding efficiency.4. We also investigated the mechanism of the error detection in the decoding process. We found that the error detection using threshold sometimes fails, and this hampers error recovering and causes image degradation.5. To prevent misdetection of error as 4, we introduced a pre-processing in the encoder, which selects only domain blocks that causes no error misdetection.6. Using encoder and decoder based on 5, we succeeded to suppress the misdetection of errors.We confirmed that the proposed method outperforms the conventional method with 2-3 dB gain of PSNR in an erroneous channel environment.