“…Low-dimensional linear models have been shown to be an accurate representation for visible and infrared spectral-reflectance functions [6], [17], [30], [32], as well as for outdoor illumination spectra [8], [9], [23], [24], [33]- [35], [37], [41]. In this section, we consider the use of linear models for the sets of observed spectral-radiance functions for different materials.…”