Patent ID: 6317512
Filing Date: 2001-11-13
Classification: G06T

Abstract:
A pattern checking method wherein a detection is made of images of two patterns each being formed with the same patterns at corresponding positions, wherein the detected images are compared with each other and a discrepancy between the images is judged as a defect, comprising the steps of:comparing output signals from an image sensor, which outputs in parallel a plurality of signals indicative of images of a certain pattern at different positions, to other signals which correspond to such signals obtained by delaying said output signals at a predetermined time period, said other signals represent images of another pattern at corresponding positions;obtaining a quantity of discrepant pixel between the images of the two patterns at the corresponding positions as a result of the comparison;detecting a positional shift amount between the images of the two patterns at corresponding positions based upon said quantity of discrepant pixel;correcting a positional shift of said image based on said detected positional shift amount every predetermined time;performing a positioning operation based on images whose positional shifts have been corrected;focusing said patterns by controlling a distance between said image sensor and said patterns; andperforming the positioning operations for said images at a large number of different positions for the images when an amount of variations in the distance where said patterns are focused onto said image sensor is greater than a predetermined value.