Camera‐based colour inspection

Abstract

Camera‐based colour measurement systems have application where it is difficult to apply a contact instrument, or where the contact instrument, because of its fixed lighting geometry, does not provide the necessary data. The paper describes the principles, procedures and precautions necessary for camera based colorimetry. Equations are presented to convert digitised R G and B values, which are system specific, into CIE X Y Z colour values, an international standard method of colour specification. It is reported that colours spaced equally in RGB values appear to have visual colour difference steps varying in size by as much as 30:1 through the different regions. The poorest colour resolution occurs for RGB values that represent dark or strongly coloured shades. At least ten bits per channel digitisation of RGB values is required to achieve a colour resolution similar to the human visual system for dark, intense shades.