Scene adaptive multiple coding scheme for robust image transmission
We propose a combined source and channel coding scheme for image transmission over noisy channels. The key component is extracting and preserving the scene information and incorporating it with unequal error protection to combat the channel errors. After hierarchical wavelet decomposition of the image, wavelet coefficients with a parent-child relationship are grouped into wavelet blocks and classified according to corresponding scenes in the original image. For each class, spatial neighborhood coefficients in the high frequency subbands are constrained so that the spatially isolated coefficients are removed and clustered coefficients are retained at the same time. All the wavelet blocks in the same class are grouped together and coded using the set partitioning in hierarchical trees (SPIHT) algorithm. High source coding efficiency is preserved even though multiple source coded bitstreams are generated since the wavelet tree structure is intact. In order to combat the channel errors, an unequal error protection strategy implemented by RCPC/CRC channel coding is designed based on the bit contribution to both PSNR and human visual sensitivity. Finally, a postprocessing method is developed at the receiving end to restore the degradation due to the residual error after channel decoding. Experimental results show that the proposed scheme is indeed able to provide protection for more important bits and more important visual content under a noisy transmission environment. In particular, the reconstructed images illustrate consistently better visual quality.