US Patent 7262854 Multi-angle colorimeter

In a multi-angle colorimeter having an illumination system that illuminates a sample surface and a plurality of light receiving systems that receive reflected light therefrom, an illumination system for orientation error detection is provided that illuminates the sample surface from substantially close direction to the normal of the sample surface. Actual measured reflectance factor is corrected based on the specific approximation function obtained from the measured reflectance factor and detected orientation error.