As an elegant generalization of wavelet transform,wavelet packet(WP) provides an effective representation tool for adaptive waveform analysis.Recent work shows that image-coding methods based on WP decomposition can achieve significant gain over those based on a usual wavelet transform.However,most of the work adopts a tree-structured quantization scheme,which is a successful technique for wavelet image coding,but not appropriate for WP subbands.This paper presents an image-coding algorithm based on a rate-distortion optimized wavelet packet decomposition and on an intraband block-partitioning scheme.By encoding each WP subband separately with the block-partitioning algorithm and the JPEG2000 context modeling,the proposed algorithm naturally avoids the difficulty in defining parent-offspring relationships for the WP coefficients,which has to be faced when adopting the tree-structured quantization scheme.The experimental results show that the proposed algorithm significantly outperforms SPIHT and JPEG2000 schemes and also surpasses state-of-the-art WP image coding algorithms,in terms of both PSNR and visual quality. As an elegant generalization of wavelet transform, wavelet packet (WP) provides an effective representation tool for adaptive waveform analysis. Recent work shows that image-coding methods based on WP decomposition can achieve significant gain over those based on a usual wavelet transform. However, most of the work adopts a tree-structured quantization scheme, which is a successful technique for wavelet image coding, but not appropriate for WP subbands. This paper presents an image-coding algorithm based on a rate-distortion optimized wavelet packet decomposition and on an intraband block-partitioning scheme.By encoding each WP subband separately with the block-partitioning algorithm and the JPEG2000 context modeling, the proposed algorithm naturally avoids the difficulty in defining parent-offspring relationships for the WP coefficients, which has to be faced when assuming the tree-structured quantization scheme.The experimental results show that the proposed algorithm significantly outperforms SPIHT and JPEG2000 schemes and also surpasses state-of-the-art WP image coding algorithms, in terms of both PSNR and visual quality.