The usage of digital cameras as luminance meters

Many luminance measuring tasks require a luminance distribution of the total viewing field. The approach of imageresolving luminance measurement, which could benefit from the continual development of position-resolving radiation detectors, represents a simplification of such measuring tasks. Luminance measure cameras already exist which are specially manufactured for measuring tasks with very high requirements. Due to high-precision solutions these cameras are very expensive and are not commercially viable for many image-resolving measuring tasks. Therefore, it is desirable to measure luminance with digital still cameras which are freely available at reasonable prices. This paper presents a method for the usage of digital still cameras as luminance meters independent of the exposure settings. A calibration of the camera is performed with the help of an OECF (opto-electronic conversion function) measurement and the luminance is calculated with the camera’s digital RGB output values. The test method and computation of the luminance value irrespective of exposure variations is described. The error sources which influence the result of the luminance measurement are also discussed.