The case for an LMS camera

Abstract

Consumer color cameras employ sensors that do not mimic human cone spectral sensitivities, and more generally do not meet the Luther condition since the accompanying color correction substantially amplifies noise in the red channel. This begs the question: if cone spectral sensitivities yield low SNR, why has the Human Visual System so evolved? We answer the above question by noting that since modern ISPs - and the ancient HVS - remove virtually all chrominance noise, chrominance denoising artifacts rather than the chrominance noise itself should be considered. While sensor green, blue are reasonable analogs of the human M, S cones, the spectral sensitivity of red is much narrower than that of L and does not overlap much with green. An imager employing L instead of red suffers from increased red noise but is also more sensitive. This allows a high SNR (L + M)/2 luminance image to be reconstructed and used for denoising. Modeling the color filter array on the human retina, with a higher density of L pixels at the expense of S pixels, further improves the red SNR without the accompanying loss of blue quality being perceptible. The resulting LMS camera outperforms conventional RGB cameras in color accuracy and luminance SNR while being competitive in chrominance quality.