8.59. Dither
This filter can reduce the number of colors in an image by reducing the levels per channel (colors and alpha). Different dithering methods can be specified to counteract quantization induced banding.
8.59.1. Activating the filter
You can access this command from the main menu through Colors → Dither….
8.59.2. Options
图 16.262. Dither filter dialog
Presets
“Presets” are a common feature for several Colors commands. You can find its description in 第 8.1.1 节 “Colors Common Features”.
Red levels, Green levels, Blue levels, Alpha levels
These sliders allow you to set the number of levels for the respective red, green blue and alpha channels.
Dithering method
Here you can specify the dithering method to use.
None
No dithering will be performed on the image.
Floyd-Steinberg
This is the most commonly used method of dithering and the default for this filter. For more information see Floyd–Steinberg dithering on Wikipedia.
Bayer
The Bayer Matrix is another common method of dithering used to reduce the number of colors. The algorithm is characterized by noticeable crosshatch patterns in the result. For more information see Ordered dithering on Wikipedia.
Random, Random covariant
These methods of dithering use randomization of the pixel values to reduce the number of colors.
Arithmetic add, Arithmetic add covariant, Arithmetic xor, Arithmetic xor covariant
These methods of dithering are spatially stable, based on magic numbers and arithmetic. For more information see a dither.
Blue Noise, Blue Noise covariant
These dithering methods using so-called blue noise have been found to be the least unsightly and distracting. For more information see Dithering in image processing on Wikipedia.
Random seed, New Seed
The Random seed box lets you choose a new seed for the randomization algorithm used in the two random dithering methods. The New Seed button picks a new random seed for you.
Input Type, Clipping, Blending Options, Preview and Split view
These are common features described in 第 8.1.1 节 “Colors Common Features”.