Multispectral system for recovering near-infrared reflectance spectra

Abstract

In this paper, we analyze an experimental system for recovering the reflectance spectra of samples in the nearinfrared region of the spectrum (NIR, 800-1000 nm). Recently, CCD cameras with improved response in the NIR have been manufactured. It is therefore possible to use this standard instrumentation to obtain information on samples in this region. The setup used in this work consisted of a conventional multispectral system of five acquisition channels with spectral bands that were equispaced in the NIR region. An automated objective lens was used to control the exposure over the CCD. By using different F-number exposure series, we obtained sets of camera responses corresponding to a group of reference samples and analyzed the dependence of the digital output levels on the lens aperture. The reconstructions obtained for a set of textile samples show that Wiener estimation and principal component analysis provide the best results. These mathematical methods provide percentages of reconstruction close to 99.8% and RMSE values close to 0.025.