The fundamentals of average local variance - Part II: Sampling simple regular patterns with optical imagery
The fundamentals of average local variance - Part II: Sampling simple regular patterns with optical imagery
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DOI：
10.1109/tip.2005.860621
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发表时间：
2006-02-01
影响因子：
10.6
通讯作者：
McCloy, KR
中科院分区：
文献类型：
--
作者：
Bocher, PK;McCloy, KR
在这项调查中，平均局部方差（ALV）函数的特性进行了研究，通过采集图像在不同的空间分辨率的构建场景的规则图案的黑色和白色广场。它示出的ALV图始终峰值在空间分辨率中的像素具有对应于场景对象之间的距离的一半的大小，并且，在非常特定的条件下，它也峰值在空间分辨率中的像素大小对应于场景对象之间的整个距离。有人认为，峰值在物距时，是一个表达式的奈奎斯特采样率。因此，该峰值的存在被示出为场景图案的相位与样本网格的相位之间的匹配的函数，即，形象当这些相位匹配时，在ALV图上产生清晰且明显的峰。在ALV图中始终出现距离一半处的峰值的事实与采样间隔（像素之间的距离）和采样单元的范围（像素的大小）相等的情况有关。因此，在两倍的奈奎斯特采样率下，图案的每个基本周期被四个像素覆盖;因此，无论样本场景相位如何，至少一个像素总是完全嵌入在一个图案元素内。如果场景中的对象以大于其范围的距离分散，则峰值将以大于1/2的因子与大小相关。这被认为是对其他人提出的结果的解释，即ALV图与场景对象大小的1/2-3/4的因子有关。
In this investigation, the characteristics of the average local variance (ALV) function is investigated through the acquisition of images at different spatial resolutions of constructed scenes of regular patterns of black and white squares. It is shown that the ALV plot consistently peaks at a spatial resolution in which the pixels has a size corresponding to half the distance between scene objects, and that, under very specific conditions, it also peaks at a spatial resolution in which the pixel size corresponds to the whole distance between scene objects. It is argued that the peak at object distance when present is an expression of the Nyquist sample rate. The presence of this peak is, hence, shown to be a function of the matching between the phase of the scene pattern and the phase of the sample grid, i.e., the image. When these phases match, a clear and distinct peak is produced on the ALV plot. The fact that the peak at half the distance consistently occurs in the ALV plot is linked to the circumstance that the sampling interval (distance between pixels) and the extent of the sampling unit (size of pixels) are equal. Hence, at twice the Nyquist sampling rate, each fundamental period of the pattern is covered by four pixels; therefore, at least one pixel is always completely embedded within one pattern element, regardless of sample scene phase. If the objects in the scene are scattered with a distance larger than their extent, the peak will be related to the size by a factor larger than 1/2. This is suggested to be the explanation to the results presented by others that the ALV plot is related to scene-object size by a factor of 1/2-3/4.