Abstract: The calibration of an imaging system having a camera (20) for capturing colour data for a target object (carcass 10) includes a primary calibration to obtain a primary transform for RGB data to enable compensation for variations in the camera operation or characteristics, and a secondary calibration obtain a secondary transform to enable compensation for local lighting conditions during capture and processing of colour data for captured images to be analysed. The calculated primary transform relates the actual measured colour data to known standard colour data for the particular standard colour specimens (31). The standard colour specimens (31) are presented in an enclosure or hood (30) to the camera under controlled illumination and with extrancous or external light being excluded from illuminating the specimens. A preliminary calibration includes calibrating the primary calibration standard colour specimens and associated controlled light source against centralised laboratory standard colours.