Image Processing Toolbox™

rgb2gray - Convert RGB image or colormap to grayscale

Syntax

I = rgb2gray(RGB) newmap = rgb2gray(map)

Description

I = rgb2gray(RGB) converts the truecolor image RGB to the grayscale intensity image I. rgb2gray converts RGB images to grayscale by eliminating the hue and saturation information while retaining the luminance.

newmap = rgb2gray(map) returns a grayscale colormap equivalent to map.

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

Class Support

If the input is an RGB image, it can be of class uint8, uint16, single, or double. The output image I is of the same class as the input image. If the input is a colormap, the input and output colormaps are both of class double.

Examples

Convert an RGB image to a grayscale image.

I = imread('board.tif');
J = rgb2gray(I);
figure, imshow(I), figure, imshow(J);

Convert the colormap to a grayscale colormap.

[X,map] = imread('trees.tif');
gmap = rgb2gray(map);
figure, imshow(X,map), figure, imshow(X,gmap);

Algorithm

rgb2gray converts RGB values to grayscale values by forming a weighted sum of the R, G, and B components:

0.2989 * R + 0.5870 * G + 0.1140 * B