8.58. Dither
| 8. The “Colors” Menu |

### 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 16.242. Dither filter dialog

Presets

  “Presets” are a common feature for several Colors commands. You can find its description in Section 8.1.1, “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 Section 8.1.1, “Colors Common Features”.

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

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