MacAdam ellipse

In the study of color vision, a MacAdam ellipse is roughly a region on a chromaticity diagram which contains all colors which are indistinguishable, to the average human eye, from the color at the center of the ellipse. Specifically, it is the standard deviation of a number of experimental color matches to the central color. Assuming a bivariate normal distribution of these match points, a MacAdam ellipse thus contains about 39% of the color match points. A 2X MacAdam ellipse will contain about 86% of the match points, and a 3X MacAdam ellipse will contain about 99% of the match points. The just-noticeable differences of chromaticity is generally taken to be a 3X MacAdam ellipse.[1] Standard Deviation Color Matching in LED lighting uses deviations relative to MacAdam ellipses to describe color precision of a light source.[2]

MacAdam ellipses for one of MacAdam's test participants, Perley G. Nutting (observer "PGN"), plotted on the CIE 1931 xy chromaticity diagram. The ellipses are ten times their actual size, as depicted in MacAdam's paper[1].
  1. ^ a b MacAdam, David Lewis (May 1942). "Visual sensitivities to color differences in daylight" (abstract). JOSA. 32 (5): 247–274. Bibcode:1942JOSA...32..247M. doi:10.1364/JOSA.32.000247.
  2. ^ "Talking Photometry - Colour Difference". Photometric Testing. Retrieved 26 March 2017.