Noise reduction in signal from imaging apparatus e.g. for semiconductor device manufacture by replacing gray scale values for pixels lying outside region of acceptable values

摘要

The method involves producing digital image data corresponding to a region of an object, and having gray scale values, forming a matrix (55) of m x n pixels (56). For each of n columns, the distribution of the number of pixels is deduced based on the level of the gray scale. Based on the distribution, a region of acceptable values of gray scale levels is determined. For all values of gray scale levels outside the region, the characteristics of the pixels assigned to these values are changed, i.e. the gray scale is replaced with a predetermined gray scale. An apparatus for reducing noise in a signal is also claimed.