Multispectral imaging: narrow or wide band filters?
Résumé
In every aspect, spectral characteristics of filters play an important role in an image acquisition system. For a colorimetric system, traditionally, it is believed that narrow-band filters give rise to higher accuracy of colour reproduction, whereas wide-band filters, such as complementary colour filters, have the advantage of higher sensitivity. In the context of multispectral image capture, the objective is very often to retrieve an estimation of the spectral reflectance of the captured objects. The literature does not provide a satisfactory answer to which configuration yields the best results. It is therefore of interest to verify which type of filters performs the best in estimating the reflectance spectra for the purpose of multispectral image acquisition. A series of experiments were conducted on a simulated imaging system, with six types of filters of varying bandwidths paired with three linear reflectance estimation methods. The results show that filter bandwidth exerts direct influence on the accuracy of reflectance estimation. Extremely narrowband filters did not perform well in the experiment and the relation between bandwidth and reflectance estimation accuracy is not monotonic. Also it is indicated that the optimal number of filters depends on the spectral similarity metrics employed.