  In previous work, it was shown that a camera can theoretically be made more
colorimetric - its RGBs become more linearly related to XYZ tristimuli - by
placing a specially designed color filter in the optical path. While the prior
art demonstrated the principle, the optimal color-correction filters were not
actually manufactured. In this paper, we provide a novel way of creating the
color filtering effect without making a physical filter: we modulate the
spectrum of the light source by using a spectrally tunable lighting system to
recast the prefiltering effect from a lighting perspective. According to our
method, if we wish to measure color under a D65 light, we relight the scene
with a modulated D65 spectrum where the light modulation mimics the effect of
color prefiltering in the prior art. We call our optimally modulated light, the
matched illumination. In the experiments, using synthetic and real
measurements, we show that color measurement errors can be reduced by about 50%
or more on simulated data and 25% or more on real images when the matched
illumination is used.
