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Convert indexed image to grayscale image


I = ind2gray(X,map)


I = ind2gray(X,map) converts the image X with colormap map to a grayscale image I. ind2gray removes the hue and saturation information from the input image while retaining the luminance.


A grayscale image is also called a gray-scale, gray scale, or gray-level image.

Class Support

X can be of class uint8, uint16, single, or double. map is double. I is of the same class as X.


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Load an indexed image into the workspace.

[X, map] = imread('trees.tif');

Convert the image to grayscale using ind2gray.

I = ind2gray(X,map);

Display the indexed image and the converted grayscale image.

title('Indexed Image')

title('Converted Grayscale Image')


ind2gray converts the colormap to NTSC coordinates using rgb2ntsc, and sets the hue and saturation components (I and Q) to zero, creating a gray colormap. ind2gray then replaces the indices in the image X with the corresponding grayscale intensity values in the gray colormap.

Introduced before R2006a

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