Dither

Reduces each color to a few shades and arranges the rounding error into a pattern, so smooth gradients read as texture instead of hard bands.

Parameter	Control	Range	Notes
Algorithm	Selector	14 patterns	Grouped as Ordered, Noise, Screen and Diffusion Look. See the table below. Cannot be modulated.
Quantize To	Selector	Color Levels, Gray Levels, Spread Only	Color Levels reduces red, green and blue to Levels shades each. Gray Levels converts to gray first, then reduces. Spread Only adds the pattern without reducing any shades. Cannot be modulated.
Levels	Trough	2 to 32	Shades kept per color. In Spread Only it sets how far the pattern spreads, so match it to the number of tones in the palette that follows.
Strength	Trough	0 to 1	0 gives plain banding with no pattern. 1 gives the full pattern.
Cell Size	Trough	1 to 32px	The picture is sampled once per cell, so larger cells give a chunkier, lower-resolution look. 1 works on every pixel.
Angle	Wheel	-180 to 180	Rotates the pattern. Halftone Dots always starts from the classic 45 degree screen angle, and Angle turns it from there.
Animate	Trough	0 to 30 Hz	How many times per second the pattern changes. 0 keeps it still.
Bias	Trough	-0.5 to 0.5	Pushes the picture lighter or darker before the shades are chosen.

Algorithms

Group	Algorithm	Look
Ordered	Bayer 2x2, Bayer 4x4, Bayer 8x8, Bayer 16x16	Regular grids. The larger the grid, the smoother the gradients.
Ordered	Bayer + Noise	A Bayer 8x8 grid with blue noise mixed in to hide the grid lines.
Noise	Blue Noise	Even, grain-like noise with no visible grid.
Noise	Gradient Noise	A fast diagonal noise, more structured than white noise.
Noise	White Noise	Pure random speckle.
Screen	Halftone Dots	Printed dots that grow with brightness.
Screen	Clustered Dot	A fixed 8 by 8 dot pattern, like an old digital printer.
Screen	Line Screen	Parallel lines that thicken with brightness.
Screen	Cross-Hatch	Two sets of lines at right angles that thicken with brightness.
Diffusion Look	Floyd-Steinberg Look, Atkinson Look	Organic worm-like patterns. Atkinson Look also crushes the brightest and darkest areas, as the early Macintosh did.

The pattern is fixed to the output frame, not to the picture. Moving content slides underneath it.

NOTE: Diffusion Look patterns approximate error diffusion within small blocks. Increasing Cell Size reduces their processing cost. In Spread Only they use Blue Noise.

NOTE: Dither does not change transparency. Parts of the picture that are empty stay empty.

To dither with a specific set of colors, set Quantize To to Spread Only and place a Palette Map later in the same chain.

Related: Posterize, Insert FX Chains.