Generating stimuli of arbitrary spectral power distributions for vision and imaging research

The spectral integrator at the University of Oslo consists of a lamp whose light is dispersed into a spectrum by means of a prism. Using a transmissive LCD panel controlled by a computer, certain fractions of the light in different parts of the spectrum is masked out. The remaining spectrum is integrated and the resulting colored light projected onto a dispersing plate. Attached to the computer is also a spectroradiometer measuring the projected light, thus making the spectral integrator a closed-loop system. One main challenge is the generation of stimuli of arbitrary spectral power distributions. We have solved this by means of a computational calibration routine: Vertical lines of pixels within the spectral window of the LCD panel are opened successively and the resulting spectral power distribution on the dispersing plate is measured. A similar procedure for the horizontal lines gives, under certain assumptions, the contribution from each opened pixel. Hereby, light of any spectral power distribution can be generated by means of a fast iterative heuristic search algorithm. The apparatus is convenient for research within the fields of color vision, color appearance modelling, multispectral color imaging, and spectral characterization of devices ranging from digital cameras to solar cell panels.