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

Apparent contrast — where it appears

How much difference an observer reports between two regions, which is not the ratio of their luminances. Edges rather than fields carry it, which is why an edge profile can set the appearance of an area it does not touch.

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

Colourfulness rises with light level; apparent contrast does not. Predicted colourfulness M for one stimulus across four decades of adapting luminance, and the exponent of the lightness curve over the same range. M rises by a factor of 2.24 — the Hunt effect, which the model does predict. The lightness exponent changes by -2.2%, and in the wrong direction — the Stevens effect, which it does not.

Brighter looks more colourful

Colourfulness rises with light level and the model predicts it. Apparent contrast is supposed to rise too, and the model does not — which turns out to be right, because the thing that actually carries contrast is the surround.

brain · Appearance One stimulus, three rooms, three appearances. The same XYZ in a dark, a dim and an average surround. The stimulus does not change and is drawn identically in all three panels; what changes is what CIECAM16 says it looks like. Predicted lightness runs from 65.6 to 57.5 — a spread of 8.1 — with chroma and colourfulness moving too. Colorimetry returns one answer here because it has nowhere to put the room.

A patch is not a scene

A paint chip is the wrong size, on the wrong background, at the wrong luminance, in the wrong surround. Every one of those is a term in an appearance model, and the model says how much each of them moves the answer — which is the difference between a caution and a prediction.

brain · Appearance

Named alongside it

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

AdaptationColour appearanceLuminanceSurroundAbsolute luminanceCIECAM16ColourfulnessThe Hunt effectLightnessSimultaneous contrastStandard observerThe Stevens effect

All concepts