Threshold Dither
threshold-dither
The threshold-dither parameter replaces the hard cutoff of threshold with a dot pattern that approximates the midtones. The output is still pure black and white, but the pattern’s density stands in for the shades that a hard cut would discard.
threshold-dither requires threshold. On its own it produces no dithering.
| Value | Algorithm |
|---|---|
floydsteinberg (or true) | Floyd–Steinberg error diffusion, the familiar fine-grained dither |
atkinson | Atkinson error diffusion, which keeps more contrast and leaves cleaner highlights |
A threshold of 50 gives the classic dithered look. Non-numeric or unrecognized values are ignored and left out of the X-Imgix-Params response header.
Atkinson leaves cleaner highlights at the same cutoff.
Pattern Size
The dot pattern is generated at the output size, not the source size. Changing w, h or dpr therefore changes the pattern, not just its scale. Two renders of the same image at different widths will not have matching dots, which matters when a dithered asset is served through a srcset.
Dithered output also compresses poorly in lossy formats, because the pattern is high-frequency detail. Prefer fm=png or fm=webp over JPEG for dithered images.