Same colour, two objects

Every pixel is three numbers. When a jacket and the sky behind it share those numbers, no tolerance can separate them — the answer is to say where, not to measure harder.

The selection only knows values

A colour selection asks one question of each pixel: how close is it to the sampled colour, in hue, chroma and lightness? It has no notion of an object. A blue jacket photographed against a blue sky is, to that question, one blue region with a slightly darker patch in it, and every setting that catches the jacket's shadowed folds also catches the sky.

Coverage before and after a region

Measured by the engine at build time on a drawn frame: a jacket (OKLCH L 0.55, C 0.11, h 252°) covering 12.5% of the frame, standing in front of a sky only three degrees of hue and seven hundredths of lightness away.

The same sample and tolerances, with and without a rectangle around the jacket
Selection	Coverage of the frame
Colour only (default tolerances)	59.4%
Colour inside a rectangle	13.9%
The jacket itself	12.5%

The rectangle does not have to be tight. It is a fence: inside it the colour test still decides each pixel, at full resolution, so the edge lands where the jacket's colour stops.

Three ways to say where

The brush paints “only here” or “not here”. Rectangles and ellipses do the same with four numbers, which is easier on a phone and exact from a keyboard. And when the object is a person, the on-device person finder can limit the change to the person, or keep it off them; its answer is a coarse map multiplied into the colour selection, so the edge is still the colour's, not the model's.

Back to the swatches

Every pixel is remapped locally — this page has no server to send to.