Signal Processing Institute, Swiss Federal School of Technology, CH-1015 Lausanne, Switzerland.
IEEE Trans Image Process. 2002;11(11):1284-94. doi: 10.1109/TIP.2002.804280.
Human observers are very sensitive to a loss of image texture in photo-realistic images. For example a portrait image without the fine skin texture appears unnatural. Once the image is decomposed by a wavelet transformation, this texture is represented by many wavelet coefficients of low- and medium-amplitude. The conventional encoding of all these coefficients is very bitrate expensive. Instead, such an unstructured or stochastic texture can be modeled by a noise process and be characterized with very few parameters. Thus, a hybrid scheme can be designed that encodes the structural image information by a conventional wavelet codec and the stochastic texture in a model-based manner. Such a scheme, called WITCH (Wavelet-based Image/Texture Coding Hybrid), is proposed. It implements such an hybrid coding approach, while nevertheless preserving the features of progressive and lossless coding. Its low computational complexity and the parameter coding costs of only 0.01 bpp make it a valuable extension of conventional codecs. A comparison with the JPEG2000 image compression standard showed that the WITCH-scheme achieves the same subjective quality while increasing the compression ratio by more than a factor of two.
人类观察者对逼真图像中图像纹理的丢失非常敏感。例如，没有精细皮肤纹理的人像图像看起来不自然。一旦图像通过小波变换分解，这种纹理就由许多低幅度和中幅度的小波系数表示。对所有这些系数的传统编码非常耗费比特率。相反，可以通过噪声过程对这种非结构化或随机纹理进行建模，并使用很少的参数对其进行特征化。因此，可以设计一种混合方案，通过传统的小波编解码器对结构图像信息进行编码，并以基于模型的方式对随机纹理进行编码。这种方案称为 WITCH（基于小波的图像/纹理编码混合）。它实现了这种混合编码方法，同时保留了渐进式和无损编码的特点。其低计算复杂度和仅 0.01 bpp 的参数编码成本使其成为传统编解码器的有价值的扩展。与 JPEG2000 图像压缩标准的比较表明，WITCH 方案在提高压缩比一倍以上的同时达到了相同的主观质量。
