Colour Science & Perception
what the eye settles, and what it cannot
Concept

Standard deviation — where it appears

The root-mean-square spread of a quantity about its mean, in the quantity's own units. It summarises a population or a process in one number and says nothing about direction, which is why a spread of readings cannot say what a process costs against a tolerance that is tighter one way than another.

Named by 2 essays across one field — each of them below, with the objects they name alongside it.

How far a fitted transform is from anybody's eyes. Five groups of three bars: for each published adaptation transform, the distance from the population's own cloud to the confusion point that transform is committed to, measured in the population's standard deviations on that point. On the protanope's point every one of them is between 2.2 and 14.4 out, and on the deuteranope's between 3.7 and 11.8. On the tritanope's, 5 of the five are within three standard deviations — indistinguishable from a member of the population. The claim that these matrices are not cone responses is safe, and the evidence for it is two points out of three.

Two points out of three

Every published adaptation transform implies three dichromat confusion points, whether or not it was fitted to any. Measured in the population's own standard deviations they are two to fourteen out on the protanope's point and four to twelve on the deuteranope's — and between half a standard deviation and two and a half on the tritanope's, which is inside the population. The claim that these matrices are not cone responses is safe. The evidence for it is two points.

matching · Gamut Where a press's variation lies, and where the tolerance charges for it. Each printed patch's sheet-to-sheet variation under four stated mixes of press variation, split along the three axes of a one-unit ΔE₀₀ tolerance at that patch, tightest first. The upper bar of each pair is the share of the variation along each axis and the lower the share of the price, averaged over 29 patches. For an even mix the tightest axis holds 1.5% of the variation and pays 29% of the price, and the loosest holds 83% and pays 36%. For inking alone the tightest axis holds 2.0% of the variation and pays 34% of the price, and the loosest holds 79% and pays 28%. For a gain-led press the tightest axis holds 1.8% of the variation and pays 29% of the price, and the loosest holds 83% and pays 39%. For a trap-led press the tightest axis holds 1.6% of the variation and pays 29% of the price, and the loosest holds 82% and pays 35%.

A press is charged for the direction it barely moves

A press run varies almost entirely along the direction a colour tolerance forgives. Split along the tolerance's own axes under four stated mixes of press variation, its tightest axis holds about one per cent of the sheet-to-sheet variation and pays a quarter to a third of the price — and on a blue overprint four fifths, for the balance between two inking units rather than the level of either.

matching · Gamut

Named alongside it

The objects these essays reach for when they reach for this one.

AnisotropyBasisCAT16Chromatic adaptationCIEDE2000Colour differenceCone fundamentalsConfusion pointDichromacyMacular pigmentObserver variabilityOrientation

All concepts