Wang Z, Bovik A C
Dept. of Electr. and Comput. Eng., Texas Univ., Austin, TX 78712-1084, USA.
IEEE Trans Image Process. 2001;10(10):1397-410. doi: 10.1109/83.951527.
The human visual system (HVS) is highly space-variant in sampling, coding, processing, and understanding. The spatial resolution of the HVS is highest around the point of fixation (foveation point) and decreases rapidly with increasing eccentricity. By taking advantage of this fact, it is possible to remove considerable high-frequency information redundancy from the peripheral regions and still reconstruct a perceptually good quality image. Great success has been obtained previously by a class of embedded wavelet image coding algorithms, such as the embedded zerotree wavelet (EZW) and the set partitioning in hierarchical trees (SPIHT) algorithms. Embedded wavelet coding not only provides very good compression performance, but also has the property that the bitstream can be truncated at any point and still be decoded to recreate a reasonably good quality image. In this paper, we propose an embedded foveation image coding (EFIC) algorithm, which orders the encoded bitstream to optimize foveated visual quality at arbitrary bit-rates. A foveation-based image quality metric, namely, foveated wavelet image quality index (FWQI), plays an important role in the EFIC system. We also developed a modified SPIHT algorithm to improve the coding efficiency. Experiments show that EFIC integrates foveation filtering with foveated image coding and demonstrates very good coding performance and scalability in terms of foveated image quality measurement.
人类视觉系统（HVS）在采样、编码、处理和理解方面具有高度的空间变异性。HVS的空间分辨率在注视点（中央凹点）周围最高，并随着离心率的增加而迅速降低。利用这一事实，可以从周边区域去除大量高频信息冗余，并且仍然重建出感知质量良好的图像。先前通过一类嵌入式小波图像编码算法，如嵌入式零树小波（EZW）和分层树中的集合划分（SPIHT）算法，已经取得了巨大成功。嵌入式小波编码不仅提供了非常好的压缩性能，而且具有这样的特性：比特流可以在任何点截断，并且仍然可以解码以重建出质量相当好的图像。在本文中，我们提出了一种嵌入式中央凹图像编码（EFIC）算法，该算法对编码比特流进行排序，以在任意比特率下优化中央凹视觉质量。一种基于中央凹的图像质量度量，即中央凹小波图像质量指数（FWQI），在EFIC系统中起着重要作用。我们还开发了一种改进的SPIHT算法以提高编码效率。实验表明，EFIC将中央凹滤波与中央凹图像编码相结合，并且在中央凹图像质量测量方面展示出非常好的编码性能和可扩展性。
