A method for analysing the color rendering of digital cameras

The paper proposes a method for studying the color rendition of digital cameras. This parameter is conventionally assessed visually by color targets in photography and design. The proposed method compares the chromaticity values of standard test objects with their measured values on a digital camera using special setup features. The setup includes a light source, a collimator for uniform illumination of a reflecting screen with a test object, and a research object, i.e., a digital camera. The camera is positioned at a 45 degree angle to the screen. This setup follows the recommendations of the Commission Internationale de l’Eclairage (CIE) for color measurements. To measure the colorimetric characteristics of the samples, the authors adopted the 0/45 illumination / observation scheme. The test object is illuminated with a light beam, the axis of which makes an angle not exceeding 10° from the normal to the sample surface. The sample is observed at an angle of 45° ± 5° from to the normal. The angle between the axis of the illuminating beam and any of its rays does not exceed 5°. A type A source (color temperature 2856 K) acts as an illuminator. Standardized reference sets of colored optical glasses (light filters) characterized by known chromaticity coordinates were chosen as test objects. To evaluate the results, specialized software has been developed that allows one to select individual pixels, calculate their brightness in order to find the chromaticity coordinates and compare the results with reference values. The method was tested using the Canon EOS 60D digital camera. At the time of measurement, digital filters for correction, anti-aliasing, sharpening, as well as color adjustment were turned off in the camera. The paper presents colorimetric measurements using 58 colored optical glasses. The averaged values fall into seven groups. The selected color space for measurements is sRGB. The measurement results proved the possibility of using the proposed technique for analysing and choosing appropriate digital recording devices for colorimetric measurements in such areas as medicine, chemistry and food industry.