Narrowing a mask to a colour

Use Selectivity to limit a shape to matching colours and brightness, and Diffusion to soften the finished layer mask.

Click a shape’s chip and enable Selectivity. Chroma limits colour differences; Luma limits brightness differences. The two combine. At zero, each axis leaves the shape unchanged. Turning Selectivity off clears both restrictions.

Measured colour. Radial samples its centre, creating a control point. Other shapes use the mean of their covered region. The panel shows Colour: Measured. Click Pick to pin a sampled colour, or Clear to return to automatic measurement.

Selectivity also applies to subtracting shapes, limiting which pixels they remove. For a luminance range requiring only a narrower brightness band, use Low and High directly.

Diffusion. Beside Opacity, this control softens the combined layer mask after all shapes are processed. It is useful for hard detected or range edges. Radial, Linear and Brush also have their own feather controls. Diffusion scales with the photograph, keeping canvas and export consistent at matching resolution.