Patent ID: 7668344

Claim:
A stain inspection method, comprising: preparing luminance data; by using a first differential filter, obtaining a group of first order differential values from luminance values of said luminance data along a first direction, obtaining a group of second order differential values from said group of first order differential values, and outputting first data in accordance with said group of second order differential values; and obtaining another group of first order differential values from luminance values of said luminance data along a second direction, different from said first direction, obtaining another group of second order differential values from said another group of first order differential values, and outputting second data in accordance with said another group of second order differential values, wherein said luminance data prepared in said preparing luminance data is obtained by compressing original luminance data or by eliminating noises from the original luminance data, and wherein noises are eliminated by using a median value obtained for a plurality of pixels.