Lossless color image compression using tuned degree-k zerotree wavelet coding

This chapter presents a lossless color image compression scheme using the degree-k zerotree coding technique. From studies carried out on the degree-k zerotree coding, it has been found that at lower bit-rates, a higher degree zerotree coding gives a better coding performance whereas at higher bit-rates, coding with a lower degree zerotree is more efficient. Hence, the degree of zerotree tested is tuned in each encoding pass in the proposed Tuned Degree-K Zerotree Wavelet (TD-KZW) coding to obtain an optimal compression performance. Since the TDKZW coder uses the set-partitioning approach similar to the Set-Partitioning in Hierarchical Trees (SPIHT) coder, it allows embedded coding and also enables progressive transmission to take place. In addition, a new spatial orientation tree (SOT) structure for color coding is also proposed here for low memory implementation of the TDKZW coder (LM-TDKZW). Simulation results on standard test images show that the proposed TDKZW coder gives a better lossless color image compression performance than the SPIHT coder. The results also show that the proposed LM-TDKZW coder not only requires as little as 6.25% of the memory needed by the SPIHT coder, it is able to achieve an almost equivalent lossless compression performance as the SPIHT coder.