Testing and optimizing the spectral response of digital cameras

Abstract

A colorimetric analysis and design method for cameras is presented which enables a camera to be used as an imaging colorimeter, capable of capturing an accurate record of the Commission Internationale de l'Éclairage (CIE) coordinates of the imaged objects. The spectral response characteristics of some of the component observers in the 1964 CIE Standard Observer average are first analysed and compared. CIE colour coordinates are calculated using both the Standard Observer average and individual observer CMFs for each of 32 test colours. The personal coordinates for each observer are then linked to differences in their visual response CMFs at the spectral level. A colorimetric testing and optimization method for cameras is then reported, which allows the colour capture properties of imaging systems to be analysed, controlled and modified. The method is based on imaging spectrally defined colour charts and is used to demonstrate that even minor differences in the chosen RGB filter/sensor characteristics substantially affect the numeric accuracy of the colour-defining information in images. Colour imaging error is quantified and minimized, first by establishing the camera RGB to CIE XYZ relationship, and then by adjusting the spectral response of the sensors. Under controlled lighting and exposure conditions, the design method enables output pixel-colour definitions that are a close analogue of the measured CIE XYZ tristimulus values for the imaged surface colours.

Keywords:

• SPECTRAL RESPONSE
• DIGITAL CAMERA
• COLORIMETRIC ANALYSIS
• CIE