Luminance calibration of the Nikon Coolpix 990 digital camera. Application to glare evaluation

In this paper, we present the luminance calibration of the Coolpix 990, a digital camera made by Nikon. We test the different settings of the camera and choose which ones will be adapted to the calibration procedure. We characterize the projection resulting from the fish-eye lens made by Nikon for this camera. After this, the procedure and the experimental set-up used to calibrate it are detailed. We show how we used both an artificial sky and a sky luminance scanner to allow the calibration on the all EV (Exposure Value) scale. We explain why the luminance is an exponential function of the lightness of the pixel, the lightness being the L* component of the pixel value expressed in the CIE Lab color space; the coefficients of this function depending on the speed and the aperture used to take the picture. We conclude with the different applications in which the Coolpix 990 could be used.