`cmap2gray`

Converts a colormap to grayscale.

Category: Graphics > Images

Syntax

g = cmap2gray(map)

Returns a colormap in which each color is replaced by its luminance.

Description

Each row is replaced by the weighted sum 0.2989*R + 0.5870*G + 0.1140*B, which approximates perceived brightness, repeated in all three channels. Pure green therefore ends up much lighter than pure blue.

Input arguments

map: m-by-3 matrix of RGB values in the range [0, 1].

Output arguments

g: m-by-3 colormap whose three columns are equal.

Example

Primaries to gray

map = [1 0 0; 0 1 0; 0 0 1];
g = cmap2gray(map)

Output

g = 3×3

    0.2989    0.2989    0.2989
    0.5870    0.5870    0.5870
    0.1140    0.1140    0.1140

See also

rgb2gray im2gray colormap gray