Do The Numbers Matter?
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Re: Do The Numbers Matter?Reply #4 on: April 11, 2020 at 3:10 pm
Mark, if you’re talking about making your own personal ellipse set, the original experiments were performed at constant luminance. From Wikipedia:
MacAdam set up an experiment in which a trained observer viewed two different colors, at a fixed luminance of about 48 cd/m. One of the colors (the “test” color) was fixed, but the other was adjustable by the observer, and the observer was asked to adjust that color until it matched the test color. This match was, of course, not perfect, since the human eye, like any other instrument, has limited accuracy. It was found by MacAdam, however, that all of the matches made by the observer fell into an ellipse on the CIE 1931 chromaticity diagram. The measurements were made at 25 points on the chromaticity diagram, and it was found that the size and orientation of the ellipses on the diagram varied widely depending on the test color.
The experiments have been extended to three dimensions:
A more general concept is that of “discrimination ellipsoids” in the entire three-dimensional color space, which would include the ability of an observer to discriminate between two different luminances of the same color. Such measurements were carried out, among others, by Brown and MacAdam in 1949, Davidson in 1951, and by Wyszecki and Fielder in 1971. It was found that the discrimination ellipsoids yielded relatively unchanging discrimination ellipses in chromaticity space for luminances between 3 and 30 cd/m.
Jim
Re: Do The Numbers Matter?Reply #6 on: April 12, 2020 at 9:41 amI have a sense that the smaller the space a colour consumes on a sheet of paper and the larger the surrounding photo, the less consequential a smallish variance would appear and conversely, the larger the presence of the colour, the more obvious and therefore the more careful one needs to be that monitor and printer cohere.
It should be true that the smaller the space a color occupies on the paper, the less influence it will have in viewer adaptation. But there are nonlinear effects like those that Land demonstrated with the Retinex work.
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