Color
Hue rotate
The colour wheel turned, with lightness left alone.
Controls
- angle
- How far the colour wheel is turned. A full turn brings the picture back to itself — the wheel has no off end
- saturation
- A multiplier, not a shift: zero drains all colour, one leaves it alone. A shift would make grey colourful, and grey has no hue
- lightness
- A number from 0.2 to 2, 1 by default.
- keep grey
- Below this much colour a pixel counts as grey and is left alone. Without it the turn drags colour out of shadow noise
- contrast
- A number from -1 to 1, 0 by default.