Stereo multispectral systems enable at the same time the acquisition of accurate spectral and depth information. The left and right cameras of the system can either present the same spectral sensitivities (e.g., a monochrome sensor with 7 different bandpass color filters sequentially placed in front of it for both cameras) or complementary sensitivities. The latter alternative can be accomplished by the utilization of two different filters or sets of filters for each camera of the stereo system. Even if each camera alone does not provide complete spectral information about the acquired scene, the estimation of the spectra becomes possible when both cameras are considered together. But since the reflectance spectrum of objects is a function of the wavelength, of the illumination angle and of the observation angle, the information from the left and the right cameras is generally different. This problem is already known from the RGB stereo imaging, and becomes even more relevant when it comes to multispectral stereo imaging, whose purpose is in addition an accurate color recording.In this paper, we analyze this problem experimentally by acquiring different series of stereo data and comparing them for determined regions of interest. We acquire two scenes under different lighting conditions with a standard color chart and objects whose reflectance spectra have a limited observation angle dependence. We utilize real multispectral data as well as spectra measured with a spectrophotometer to verify camera acquisition and compare them for different observation angles. We then estimate the acquired spectra using several of the possible spectral compositions, given by all the color channels available for the left and for the right camera. These estimated spectra are compared to the ground truth data and we show that the stereo system with 7 channels cameras using only 3 color channels from one camera and the 4 complementary color channels from the other camera has a good colorimetric accuracy.
Julie Klein, Til Aach, "Spectral and Colorimetric Constancy and Accuracy of Multispectral Stereo Systems" in Proc. IS&T CGIV 2012 6th European Conf. on Colour in Graphics, Imaging, and Vision, 2012, pp 239 - 246, https://doi.org/10.2352/CGIV.2012.6.1.art00042