Multilevel DCT-based zerotree image coding

Image and video coding is fundamental to data storage and transmission. JPEG 2000 is the latest international image coding standard which exploits wavelet transform for image compression. Zerotree coding structure is an efficient algorithm for coding of wavelet transform coefficients. However, implementation complexity of wavelet transform and long coding process of zerotree structure may limit the application in some cases. In this paper, an idea of multilevel DCT-based zerotree image coding is proposed, in which Wavelet Transform (WT) is replaced by Discrete Cosine Transform (DCT) and DCT coefficients are regrouped into subbands of different frequencies. Furthermore, a new zerotree coding structure is proposed to reduce the complexity of zerotree coding process. A conventional zerotree with a parent-child relation of 2×2 offspring is expanded to the one of 4×4 offspring. Coefficients reorder and inverse DCT are needed when DCT transform size is not a power of 4. This expansion makes each parent node of zerotree coding structure have more child nodes and, therefore, reduce the complexity of encoding process. Simulation results of images with different spatial resolutions are presented to show the advantage of the proposed algorithm. The proposed multi-level DCT-based zerotree image coding algorithm performs similar coding performance as the SPIHT method. The zerotree coding structure with a parent-child relation of 4×4 pixels can significantly reduce the complexity of high-bitrate coding process without sacrificing image subjective quality.