Patent ID: 7266232

Claim:
An apparatus for inspecting a pattern on an object, comprising: an image pickup device for performing an image pickup of an object to acquire data of a gray-scale inspection image; a memory for storing data of a reference image; a region class specifying circuit for specifying a region class to which each pixel of said inspection image belongs on the basis of a pixel value of said reference image; and a check circuit for checking each pixel of said inspection image by using a parameter value in accordance with a corresponding region class, wherein the pattern on said object has periodicity and said inspection image is part of an object image acquired by said image pickup device, said memory stores a region away from said inspection image by an integral multiple of a cycle of said pattern as said reference image, said region class specifying circuit generates a histogram of pixel values of said reference image and specifies said region class on the basis of said histogram, and said parameter value is a value corresponding to at least one of a differential image between said inspection image and said reference image, a normalized image which is obtained by normalizing pixel values of said differential image with a differential statistics feature value, and an image which is obtained by smoothing said normalized image.