Apparatus and method for evaluating metal surface texture

A texture evaluation apparatus of a metal surface, comprising:

• a camera configured to have three spectral sensitivities (S1(λ), S2(λ), S3(λ)) linearly and equivalently converted to a CIE XYZ color matching function;
• an arithmetic processor configured to obtain and compute data by conversion of an image that has three spectral sensitivities and that is obtained by the camera into tristimulus values X, Y and Z in a CIE XYZ color system;
• and
• a light source configured to illuminate a metal surface, wherein
• the arithmetic processor is configured to:
• set a specified inspection area out of data obtained by imaging the metal surface;
• divide the inspection area into grids in coordinates corresponding to a color space in an XYZ color system, and integrate number of pixels included in each grid with respect to an inspection plane and a reference plane, so as to create respective color space histogram distributions in the XYZ color system;
• and
• identify centers of the two color space histogram distributions of the inspection plane and the reference plane, and compute a texture spread index indicating a difference in spread between the color space histogram distributions by shifting the center of one of the color space histogram distributions to be closer to the other color space histogram distribution.