Measurement of color matching functions using a digital micro-mirror device

Abstract

As many kinds of high-quality color imaging devices are wide spread, it is required to match color appearances between different devices. However, the tristimulus values of the stimuli in different devices are not always the same when they are visually matched. One hypothesis to explain this contradiction is that the color matching functions (CMFs) to calculate tristimulus values, defined by CIE in 1931, cannot apply to real observers as each observer has different CMFs. To test this hypothesis, we built a compact apparatus with the use of a digital micro-mirror device (DMD) to measure CMFs of individual observers.

The experiment was conducted with a Maxwellian view optical system. The system can present a test stimulus whose spectral power distribution can be arbitrarily set by adjusting the power of every monochromatic light between 400 to 700 nm with a step of 10 nm. This can be realized by selectively switching DMD, on which the spectrally decomposed light using a diffraction grating is focused. We used 32 independent compound lights as a test stimulus. The observer adjusted the color of the test stimulus to match that of the reference white. We used two-degree bipartite field to present the test and the reference stimuli.

Three observers conducted five to ten sessions. From those results, we estimated the individual CMFs using linear algebraic algorithm by assuming the additivity of CMFs. The CMFs obtained were different among observers, and also different from that of the CIE standard observer. The mean CMFs of these three observers, however, is similar to that of the CIE standard observer. Our results indicate that the optical system we proposed can be used for precise measurement of CMFs as well as traditional colorimeters and that there are significant differences in CMFs among observers.