Illuminant Influence on the Reconstruction of NIR Spectra

In order to recover spectral reflectances or transmittances using a multispectral imaging based technique, it is necessary to know the spectral radiance of the illuminant used to light the samples in the acquisition process. In this study, we analyzed the influence of the spectral distribution of the illuminant on the reconstruction of spectral reflectances in the near infrared region of the spectrum (NIR). We considered a set of 30 textile samples with different spectral reflectance in this region. We tested the performance of a principal component analysis (PCA) based method and a non-linear estimation method (NLE), which allow us to obtain the spectral reflectance of samples in the NIR region from a small number of measurements performed with a CCD camera. Using numerical simulation, we analyzed the number and shape of the optimum filters that need to be used in the acquisition channels in order to obtain good spectral reconstructions under several lighting conditions. Finally, we studied the quality of the reconstructions with a set of commercially available filters which are similar to the optimum filters obtained in the simulations. The results obtained show that the reconstruction does not depend heavily on the illuminant used. This indicates that, with the same set of filters, we can obtain good reconstructions for different types of illuminant.