Remarks on signal-processing explanations of the trichromacy of vision

We present criticism of signal-processing arguments recently used to explain the trichromacy of color vision. In particular, we note that illuminant spectral power distributions (SPD's) can be metameric even when the signal-processing arguments state that trichromatic vision represents such SPD's without ambiguity. Being statistical in nature, these arguments need not apply to each individual SPD; however, further use of the arguments calls for attributing them to some ensemble of SPD's and then testing whether the ensemble satisfies the underlying statistical assumptions.