### 8.58. 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.

#### 8.58.1. Activating the Filter

This filter is found in the main menu under Colors → Dither….

#### 8.58.2. Options

Figure 16.230. Dither filter dialog

Presets, Input Type, Clipping, Blending Options, Preview, Merge filter, Split view

  | Note
  These options are described in Section 8.1.2, “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

  This option controls the randomness of the filter. The Random seed box lets you manually enter a seed for the randomization algorithm used. You can also generate a random seed by pressing the New Seed button. If the same random seed is used in the same situation, the filter produces exactly the same results. A different random seed produces different results.

8.57. Color to Alpha… |  | 8.59. RGB Clip

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