First, nonlinear stack filter is applied to estimate the maximum and minimum of noise-free image's gray scale value in a local region.
首先非线性堆滤波器用于求出图象某象素点邻域内的灰度最大值与最小值的最优估计，然后以此两估计值之差代替原象素点灰度值。
The extracted objects with different ranges usually have different distribution of gray scale value, due to uneven distribution of light and various properties of the crack background of fingerprints.
由于光线分布不均匀或斑块噪音干扰等原因，往往使所要处理的指纹的灰度值分布缺乏均匀性。
First, we standardized the size, variance of gray scale and mean value of gray scale of the motor vehicle plate images.
首先，对机动车号牌图像进行大小、灰度方差、灰度均值的标准化处理。
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