dither (Image Processing Toolbox User's Guide)

Image Processing Toolbox User's Guide

Convert an image, increasing apparent color resolution by dithering

Syntax

```
X = dither(RGB,map)
BW = dither(I)
```

Description

X = dither(RGB,map) creates an indexed image approximation of the RGB image in the array RGB by dithering the colors in the colormap map. The colormap cannot have more than 65,536 colors.

X = dither(RGB,map,Qm,Qe) creates an indexed image from RGB, specifying the parameters Qm and Qe. Qm specifies the number of quantization bits to use along each color axis for the inverse color map, and Qe specifies the number of quantization bits to use for the color space error calculations. If Qe < Qm, dithering cannot be performed, and an undithered indexed image is returned in X. If you omit these parameters, dither uses the default values Qm = 5, Qe = 8.

BW = dither(I) converts the intensity image in the matrix I to the binary (black and white) image BW by dithering.

Class Support

RGB can be uint8, uint16, single, or double. I can be uint8, uint16, int16, single, or double. All other input arguments must be double. BW is logical. X is uint8, if it is an indexed image with 256 or fewer colors; otherwise, it is uint16.

Algorithm

dither increases the apparent color resolution of an image by applying Floyd-Steinberg's error diffusion dither algorithm.

Example

Convert intensity image to binary using dithering.

I = imread('cameraman.tif');
BW = dither(I);
imshow(I), figure, imshow(BW)

See Also

rgb2ind

References

[1] Floyd, R. W., and L. Steinberg, "An Adaptive Algorithm for Spatial Gray Scale," International Symposium Digest of Technical Papers, Society for Information Displays, 1975, p. 36.

[2] Lim, Jae S., Two-Dimensional Signal and Image Processing, Englewood Cliffs, NJ, Prentice Hall, 1990, pp. 469-476.

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