Comparison of the accuracy of various transformations from multi-band images to reflectance spectra

This report provides a comparative study of the spectral and colorimetric accuracy of various transformations from multi-band digital signals to spectral reflectance. The multiband channels were obtained by multi-channel visible-spectral imaging (MVSI) using a monochrome CCD and two different filtering systems. In the first system we used a liquid-crystal tunable filter (LCTF) capturing 31 narrow-band channels. We also used a filter wheel with a set of 6 glass filters imaging with and without an extra Wratten absorption filter giving a total of 12 channels. Four different mathematical methods were tested to derive reflectance spectra from digital signals: pseudo-inverse, eigenvector analysis, modified-discrete sine transformation (MDST) and non-negative least squares (NNLS). We also considered two different approaches to sampling the digital signals; in one approach we averaged the digital counts