Black and white channel filters

A coloured filter on black-and-white film let its own colour through and held the opposite back. In a picture that is already digital the same thing is three weights, and that is all it is.

A filter is a channel mix

Each preset is a weighted sum of a pixel's linear red, green and blue light, normalised so the weights add to one, carried back onto OKLab lightness. Weight red heavily and anything red becomes light while anything blue — the sky — becomes dark, which is the red filter's famous dark sky.

The weights behind each preset (red, green, blue)
Preset	Weights	In short
Neutral	perceptual L	Perceptual lightness (OKLab L): every colour keeps the lightness it appears to have.
Red	0.85 · 0.15 · 0.00	Darker blue skies and greenery, lighter skin and lips; the classic landscape filter.
Orange	0.60 · 0.35 · 0.05	Between red and yellow: skies darken, skin smooths, haze is cut.
Yellow	0.45 · 0.50 · 0.05	A moderate darkening of blue sky; foliage and skin stay close to neutral.
Green	0.20 · 0.70 · 0.10	Lighter foliage, darker reds; skin gains tone and freckles show.
Blue	0.10 · 0.25 · 0.65	Haze and blue skies go pale, reds and skin go dark, freckles stand out.

Four subjects under each preset

The greys below are OKLab lightness values (0 black, 1 white) computed by the engine when this page is built, for four subjects: blue sky #599fd8 (L 0.68); skin #c8997b (L 0.72); foliage #518133 (L 0.55); red flower #c53637 (L 0.55).

Resulting lightness, by preset
Preset	Blue sky	Skin	Foliage	Red flower
Neutral	0.68	0.72	0.55	0.55
Red	0.52	0.81	0.47	0.78
Orange	0.60	0.78	0.50	0.70
Yellow	0.63	0.75	0.53	0.65
Green	0.69	0.71	0.56	0.52
Blue	0.82	0.64	0.44	0.45

Picking one

Landscapes with sky: red or orange. Portraits: yellow or orange for smoother skin, green when you want texture and freckles. Haze and a soft distant scene: blue. And when two colours of equal lightness merge into one grey, any filter that weights them differently pulls them apart again.

Back to the swatches

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