感兴趣区域(ROI)编码可以在低码率条件下获得高质量的局部感兴趣区域,或在图像渐进传输中使感兴趣区域获得优先传输。本文在分析了当前各类ROI 编码方法的基础上,基于SPIHT 算法提出了一种支持多个任意形状感兴趣区域并生成可任意截断码流的ROI 编码算法。该算法在SPIHT 算法中嵌入了重要系数的ROI 掩膜信息,使编码器同步地进行图像和ROI 形状的编码,使得生成的码流具有任意可截断的特性。文中还就图像ROI 编码的质量评价指标进行了讨论,并给出了一种充分考虑ROI 和背景的重要性与面积比例差别的图像质量评价指标,称为重要性-面积加权峰值信噪比(WPSNR)。实验结果表明,该算法支持有损到无损的多个任意形状ROI 的图像编码,而且ROI 优先级可调,能够生成具有嵌入式可截断性质的码流,在任意地方截断仍能保证解码器所需的图像信息和ROI 掩膜信息,且计算复杂度和SPIHT 相当,压缩效果高于BbB 移位算法。适用于低码率应用或感兴趣优先渐进传输的应用。

Based on the analysis of the current kinds of Region of Interest (ROI) coding, a mask embedded SPIHT algorithm was proposed, which supported multiple ROI in arbitrary shape. The innovation of proposed algorithm was that the coding of ROI mask was embedded into the SPIHT coding process. As the image and the mask information were coded synchronously, the bits stream could be truncated arbitrarily. Image quality evaluation method for ROI coding was also discussed. An image quality evaluation value called importance & area Weighted PSNR (WPSNR) was proposed by fully considering importance differences and area ratio between ROI and background. Experimental results show that proposed algorithm supports the compressing of multiple arbitrary shape ROI images from loss to lossless compression with configurable ROI priority. The generated bit stream could be truncated at any place, and the decoder can still decode image and ROI mask information well. Proposed algorithm was proved that it had a better performance than BbB-shift method. As the computational complexity of proposed coder was close to SPIHT, it can be used for ROI coding in low-rate applications or ROI preferential progressive transmission.