From real spectroradiometric data, we propose an algorithm to obtain the color-matching functions of any digital camera, correctly weighted and according to the corresponding white balance, from the relative scaling of their complete (3-D) spectral responsivities. Thanks to this algorithm, it is possible to predict the RGB digital levels of any digital camera in realistic illumination-scene environments –spatially non-uniform illumination field, variable chromaticity and large dynamic range of luminance levels–, opening the possibility to transform any digital camera into a tele-colorimeter. The illumination-scene test was a Macbeth Color Checker Chart under three different light sources (halogen, metal halide and daylight fluorescent lamps), provided by a non-standard light box. The results confirmed that it is possible to predict any RGB digital levels varying exclusively the f-number of the camera zoom lens.