Doug Kerr
Well-known member
We occasionally find manufacturers touting the close approach to true chromatic neutrality of reflective targets by saying, for example, "guaranteed to less than one unit of a and b in the L*a*b color space".
Note that the a*-b* plane in the L*a*b color space is not a chromaticity plane, but rather a chrominance plane.
Simplistically, this means that, for a given chromaticity, the ordinates a* and b* vary with the value of L*.
Thus these three L*a*b* triples represent reflective colors with the same reflective chromaticity, the second having a "one-stop greater" overall reflectance:
50, 1, 0
66.5, 1.25, 0
This is of course not a big deal, and "less than one unit" certainly gives a broad and useful idea of the general neighborhood of the departure from true neutrality. "Less than 1 unit" is usefully distinguished from "less than 3 units".
But in a field where manufacturers strive to claim greater neutrality of their product than some other one (but maybe not by very much), let's not think that it is truly "quantitative". It's more in the vein of "Firewood - truckload $75.00".
And of course we all find clues in these statements about the actual awareness of these manufacturers of concepts of colorimetry, which we wouldn't be at all concerned about if they were hawking breadboxes.
Note that the a*-b* plane in the L*a*b color space is not a chromaticity plane, but rather a chrominance plane.
Simplistically, this means that, for a given chromaticity, the ordinates a* and b* vary with the value of L*.
Thus these three L*a*b* triples represent reflective colors with the same reflective chromaticity, the second having a "one-stop greater" overall reflectance:
50, 1, 0
66.5, 1.25, 0
This is of course not a big deal, and "less than one unit" certainly gives a broad and useful idea of the general neighborhood of the departure from true neutrality. "Less than 1 unit" is usefully distinguished from "less than 3 units".
But in a field where manufacturers strive to claim greater neutrality of their product than some other one (but maybe not by very much), let's not think that it is truly "quantitative". It's more in the vein of "Firewood - truckload $75.00".
And of course we all find clues in these statements about the actual awareness of these manufacturers of concepts of colorimetry, which we wouldn't be at all concerned about if they were hawking breadboxes.