A hybrid SPIHT-EBC image coder

For images with textures, the high frequency wavelet coefficients are likely to become significant after few coding passes of the set partitioning in hierarchical trees (SPIHT) algorithm, which degrades substantially the coding performance. A hybrid image coder using SPIHT and embedded block coding (EBC) is thus proposed. In which, wavelet coefficients of the low frequency subbands representing the low frequency components of images are still coded by using SPIHT; wavelet coefficients of the high frequency subbands most likely representing the high-detail textures are coded by using EBC. The intermediate coding results of SPIHT can be used as estimates to facilitate the coding operations of EBC, which takes both of the well defined hierarchical tree structure across wavelet subbands and energy clustering within each subband into account to improve the compression performance. Experimental results show that EBC outperforms SPIHT for coding images at middle-high rates of bits per pixel, whereas SPIHT is preferable to EBC at low rates of bits per pixel. As expected, the hybrid SPIHT-EBC coder is comparable with SPIHT and EBC at low and middle-high rates of bits per pixel, respectively, which demonstrates the overall coding performance can be improved by using the proposed hybrid coder.