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

Constancy — where it appears

The everyday fact that a surface looks about the same colour under lights that differ enormously, and the problem of explaining how. It is ill-posed as stated — a reddish surface under white light and a white surface under reddish light send the same signal — so every account of it is a prior about scenes rather than a computation from the image.

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

Recovering the lamp from a highlight rather than from an assumption. A green scene under illuminant A. The faint curve is the true lamp; the solid one is what the interface component of the glossy surfaces recovers, which is 0.30° from it. Grey-world on the same scene is 42.1° and max-RGB 17.5°, because both are assumptions about the surfaces and a Fresnel reflection is not.

The highlight is the white balance

Every estimator a camera uses is an assumption about the scene wearing the costume of a measurement. The specular component of a glossy surface is not — it carries the illuminant to within a third of a degree on a scene where averaging is fifty times worse, and it does so without knowing what colour the paint underneath is.

imaging · Capture A correction an observer could have been born with, fitted on half the census and tested on the other. The same six models, each scored twice: on the seven census rows the fixed matrices were fitted to, and on the seven they were not. The split alternates by position so both halves contain daylight changes and discharge lamps. The upper bar is in sample and the lower is out, on a logarithmic axis. For the four models with nothing fitted the two bars differ only because the halves are different questions. For the two fitted ones the gap is the finding, and it is largest where it matters least: bolting a fixed correction onto the von Kries gain takes it from 1.2724 to 1.2592 on the rows it was fitted to, and from 1.3511 to 1.3679 — worse — on the rows it was not. There is no correction to the diagonal that an observer could arrive with.

A model is a claim about what can be known

The exact answer to chromatic adaptation is nine numbers, and the nine numbers are the change of light itself. A model whose parameters are quantities the observer cannot obtain is not a worse model of the same thing — it is a model of something else, and counting parameters without asking where they come from hides the difference.

scene · Scene

Named alongside it

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

Angular errorBasisCamera rawChromatic adaptationDichromatic modelFresnelThe grey-world assumptionHeld-outIlluminantIlluminant estimationInverse problemMatrix

All concepts