Tunable Filter Improves Multispectral Imaging

Multispectral image acquisition promises to overcome such limitations of three-channel image capture as its dependency on consistent illumination. Researchers from École Nationale Supérieure des Télécommunications in Paris implemented a multispectral imaging system comprising a monochrome CCD camera and a liquid crystal tunable filter whose spectral transmittance can be controlled electronically. They evaluated two approaches to output conversion for device-independent color data and recommended an acquisition model with separate normalization for each channel, the use of principal eigenvectors to estimate spectral reflectance based on responses through several filters, and the regression techniques to obtain colorimetric information from camera responses. In the October issue of Optical Engineering, they reported that their system showed good colorimetric and spectrophotometric quality.