In digital image capturing, the camera signals produced by D65 illuminant, once translated into tristimulus values of the CIE 1931 standard colorimetric observer, are considered appropriate for an accurate rendering. The image likelihood requires that the camera-tristimulus values, for any illuminant other than D65, must be transformed into the corresponding ones produced by the D65 illuminant. Many techniques exist for producing this transforma-tion with different performances [1]. In digital image capturing, this transformation requires color constancy [2][3][4][5][6][7] [8]. This research is for a transformation suited to realize perfect color constancy or perfect illuminant discounting (although the perfect color constancy and the perfect illuminant discounting are nonexisting for human color vision) by using the color-vision model based on the Optical Society of America-Uniform Color Scales (OSA-UCS) system [9][10]. This transformation is repre-sented by a matrix obtained by minimizing the Root Mean Square value between the pairs of the uniform scale chromatic responses related to tristimulus values of the 24 color samples of the Macbeth ColorChecker, measured under a pair of different illumi-nants, one of which is D65. The solution is obtained by a conver-gent iteration. This transformation is a color conversion, not a simple white conversion. The performance of the result is quantified by a color difference computation.