Field D J
Physiological Laboratory, University of Cambridge, UK.
J Opt Soc Am A. 1987 Dec;4(12):2379-94. doi: 10.1364/josaa.4.002379.
The relative efficiency of any particular image-coding scheme should be defined only in relation to the class of images that the code is likely to encounter. To understand the representation of images by the mammalian visual system, it might therefore be useful to consider the statistics of images from the natural environment (i.e., images with trees, rocks, bushes, etc). In this study, various coding schemes are compared in relation to how they represent the information in such natural images. The coefficients of such codes are represented by arrays of mechanisms that respond to local regions of space, spatial frequency, and orientation (Gabor-like transforms). For many classes of image, such codes will not be an efficient means of representing information. However, the results obtained with six natural images suggest that the orientation and the spatial-frequency tuning of mammalian simple cells are well suited for coding the information in such images if the goal of the code is to convert higher-order redundancy (e.g., correlation between the intensities of neighboring pixels) into first-order redundancy (i.e., the response distribution of the coefficients). Such coding produces a relatively high signal-to-noise ratio and permits information to be transmitted with only a subset of the total number of cells. These results support Barlow's theory that the goal of natural vision is to represent the information in the natural environment with minimal redundancy.
任何特定图像编码方案的相对效率，都应该仅相对于该编码可能遇到的图像类别来定义。因此，为了理解哺乳动物视觉系统对图像的表征方式，考虑自然环境中的图像（即有树木、岩石、灌木丛等的图像）的统计数据可能会有所帮助。在本研究中，比较了各种编码方案在表征此类自然图像中的信息方面的表现。此类编码的系数由响应空间局部区域、空间频率和方向的机制阵列表示（类伽柏变换）。对于许多类别的图像，此类编码并非表示信息的有效方式。然而，用六幅自然图像获得的结果表明，如果编码的目标是将高阶冗余（例如相邻像素强度之间的相关性）转换为一阶冗余（即系数的响应分布），那么哺乳动物简单细胞的方向和空间频率调谐非常适合对此类图像中的信息进行编码。这种编码产生相对较高的信噪比，并允许仅用细胞总数的一个子集来传输信息。这些结果支持了巴洛的理论，即自然视觉的目标是以最小的冗余来表征自然环境中的信息。
