A Measurement Method for Spectral Responsivity of Digital Cameras with Tone Characteristics Compensation per Pixel

Abstract

Colour signal outputs from digital cameras can be calculated from spectral distribution of an illumination, spectral reflectance of a shooting object, and spectral responsivity of a camera. The methods of measuring spectral distribution of illuminations and spectral reflectance of objects have been established unambiguously, and their characteristics are available from various databases. However, no accurate methods have been clearly defined regarding the measurement of the spectral responsivity characteristics of digital cameras. For objective assessment of the performance of digital cameras which capture colour images and output corresponding colour information in red - green - blue digital image data, proposed methods incorporate measurements of characteristics for spectral responsivity and related items. In this paper, by adopting compensation of tone characteristics for each pixel, the authors developed yet another new method of measurements to overcome some possible defects in the previously proposed methods. The paper describes an arrangement of equipment, definition of test chart and raw data handling together with some worked examples. The newly developed method has made it possible to measure the spectral responsivity characteristics of digital cameras accurately.