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imapprox - Approximate indexed image using one with fewer colors

Syntax

[Y,newmap] = imapprox(X,map,n) [Y,newmap] = imapprox(X,map,tol) Y = imapprox(X,map,newmap) Y = imapprox(...,dither_option)

Description

[Y,newmap] = imapprox(X,map,n) approximates the colors in the indexed image X and associated colormap map by using minimum variance quantization. imapprox returns the indexed image Y with colormap newmap, which has at most n colors.

[Y,newmap] = imapprox(X,map,tol) approximates the colors in X and map through uniform quantization. newmap contains at most (floor(1/tol)+1)^3 colors. tol must be between 0 and 1.0.

Y = imapprox(X,map,newmap) approximates the colors in map by using colormap mapping to find the colors in newmap that best match the colors in map.

Y = imapprox(...,dither_option) enables or disables dithering. dither_option is a string that can have one of these values.

Value	Description
`{'dither'}`(default)	Dithers, if necessary, to achieve better color resolution at the expense of spatial resolution.
`'nodither'`	Maps each color in the original image to the closest color in the new map. No dithering is performed.

Class Support

The input image X can be of class uint8, uint16, or double. The output image Y is of class uint8 if the length of newmap is less than or equal to 256. If the length of newmap is greater than 256, Y is of class double.

Algorithm

imapprox uses rgb2ind to create a new colormap that uses fewer colors.

Examples

Approximate the indexed image trees.tif by another indexed image containing only 16 colors.

[X, map] = imread('trees.tif');
[Y, newmap] = imapprox(X, map, 16);
figure, imshow(Y, newmap)