A pattern inspection method and apparatus in which an image of a first pattern formed on a sample and an image of a second pattern formed on the sample is detected. At least one of the first pattern image and the second pattern image is converted to a gray level so as to be substantially the same with each other by linear combination including a gain and offset. A defect of the sample is detected by using the first pattern image and the second pattern image at least one of which has been converted to the gray level and a result of the detection is outputted to an external storage or processor by a communication arrangement.