Visual sensitivity, blur and the sources of variability in the amplitude spectra of natural scenes
Visual sensitivity, blur and the sources of variability in the amplitude spectra of natural scenes
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DOI：
10.1016/s0042-6989(97)00181-8
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发表时间：
1997-12-01
期刊：
影响因子：
1.8
通讯作者：
Brady, N
中科院分区：
文献类型：
--
作者：
Field, DJ;Brady, N
许多研究人员建议，为了理解视觉通路中细胞的响应特性，我们必须考虑自然环境的统计结构。在本文中，我们关注这种结构的一个方面，即由自然场景的幅度或功率谱描述的相关结构。我们提出，考虑图像光谱的主要洞察力是理解细胞对不同空间频率的相对灵敏度。本研究采用了一个模型，其中峰值灵敏度作为频率的函数随线性带宽的增加而恒定(即在八度内近似恒定)。在这样的模型中，作为其最佳(或中心)空间频率的函数，单元的‘’响应量‘’(即，矢量长度)增加到约20cyc/deg，结果是对其幅值频谱通常下降为1/f的自然场景的响应大致恒定到20cyc/deg的代码。评估该灵敏度模型的一个重要考虑因素是，自然场景在其幅值频谱中表现出相当大的变化性，各个场景表现出通常比1/f更陡峭或更浅的衰减，在一组校准的自然图像上使用一种新的图像结构量度(校正对比度光谱或RCS)，表明光谱中的可变性的很大一部分是由于不同尺度上局部结构的稀疏性的差异，也就是说，被聚焦的图像将具有跨尺度具有大致相同幅度的结构(例如，边缘)，也就是说，在一些图像中高频能量的损失是由于包含结构的区域数量的减少而不是该结构的幅度，聚焦图像将具有跨尺度的结构(例如，边缘)，该结构具有大致相等的大小，但在结构覆盖的区域中可能不同。尽管其幅度谱中的可变性，但RCS的斜率被发现提供了对各种场景的物理模糊的合理预测，它还被发现产生了由人类受试者判断的对感知模糊的良好预测。(C)1997年爱思唯尔科学有限公司。
A number of researchers have suggested that in order to understand the response properties of cells in the visual pathway, we must consider the statistical structure of the natural environment, In this paper, we focus on one aspect of that structure, namely, the correlational structure which is described by the amplitude or power spectra of natural scenes, We propose that the principle insight one gains from considering the image spectra is in understanding the relative sensitivity of cells tuned to different spatial frequencies, This study employs a model in which the peak sensitivity is constant as a function of frequency with linear bandwith increasing (i.e., approximately constant in octaves), In such a model, the ''response magnitude'' (i.e., vector length) of cells increases as a function of their optimal (or central) spatial frequency out to about 20 cyc/deg, The result is a code in which the response to natural scenes, whose amplitude spectra typically fall as 1/f,is roughly constant out to 20 cyc/deg, An important consideration in evaluating this model of sensitivity is the fact that natural scenes show considerable variability in their amplitude spectra with individual scenes showing falloffs which are often steeper or shallower than 1/f, Using a new measure of image structure (the ''rectified contrast spectrum'' or ''RCS'') on a set of calibrated natural images, it is shown that a large part of the variability in the spectra is due to differences in the sparseness of local structure at different scales, That is, an image which is ''in focus'' will have structure (e.g., edges) which has roughly the same magnitude across scale, That is, the loss of high frequency energy in some images is due to the reduction of the number of regions that contain structure rather than the amplitude of that structure, An ''in focus'' image will have structure (e.g., edges) across scale that have roughly equal magnitude but may vary in the area covered by structure, The slope of the RCS was found to provide a reasonable prediction of physical blur across a variety of scenes in spite of the variability in their amplitude spectra, It was also found to produce a good prediction of perceived blur as judged by human subjects. (C) 1997 Elsevier Science Ltd.