Colour Science & Perception
what the eye settles, and what it cannot
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The thread: Identical, and asserted

"These two patches are the same colour" is the most repeated and least checkable sentence in perception, because the whole point is that it does not look true. Every instance here is an assertion in code.
on a dark fieldon a light fieldboth patches are #818181asserted equal What the brain does

These two patches are identical

It is the most repeated and least checkable sentence in visual perception, because the whole point is that it does not look true. Every instance on this site is an assertion in code that stops the build if it ever stops being the case.

 one value on the left, the same value on the rightluminance profileboth plateaux are #898989asserted equal What the brain does

Brightness is inferred from edges

The Cornsweet effect makes two identical regions look different by altering nothing except a narrow band at the boundary between them. Cover the boundary and the difference vanishes, which says the visual system is reconstructing surfaces rather than reading off intensities.

 on a dark fieldon a light fieldboth patches are #868686asserted equal Matching and measuring

Matching is not appearance

CIE XYZ predicts when two lights will look the same under identical viewing conditions. It was never a model of how anything looks, and most of the confusion in applied colour comes from using it as one.

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