A high performance fixed rate compression scheme for still image transmission

Variable length source coding schemes have a very painful drawback when it comes to transmission of compressed images. Thus the authors restrict themselves to fixed rate source coding schemes, that do not have the problems of re-synchronization or complete loss of information in the case of uncorrectable transmission errors. In the paper, a high performance source coding scheme based on the discrete wavelet transform (DWT) with an additional DCT for the low frequency sub-image and a product pyramid vector quantizer (PPVQ) utilizing trellis coded quantization (TCQ) is proposed which gives close to optimum results compared to variable length coding (VLC). This together with the ability to calculate the bit-sensitivity of the compressed image data enables one to perform a highly efficient unequal error protection for image transmission over noisy channels. Simulation results show a source coding degradation of only 0.5-0.7 dB in PSNR due to fixed rate coding compared to the best found VLC scheme. In addition, applying combined source anti-channel coding and looking at the performance after transmission over an additive white Gaussian noise (AWGN) channel, the proposed scheme outperforms all other known fixed rate schemes, even a sophisticated VLC scheme based also on the DWT and especially has gains of up to 5 dB in PSNR and up to 3.5 dB in E_S/N₀ compared to JPEG