ind2gray

Convert indexed image to grayscale image

Syntax

I = ind2gray(X,cmap)

Description

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

Examples

Convert Indexed Image to Grayscale

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.

imshow(X,map)
title('Indexed Image')

figure
imshow(I)
title('Converted Grayscale Image')

Input Arguments

X — Indexed image

numeric array

Indexed image, specified as a numeric array of any size and dimensionality.

Data Types: single | double | uint8 | uint16

cmap — Colormap

c-by-3 numeric matrix

Colormap associated with indexed image X, specified as a c-by-3 numeric matrix with values in the range [0, 1]. Each row is a three-element RGB triplet that specifies the red, green, and blue components of a single color of the colormap.

Data Types: double

Output Arguments

I — Grayscale image

numeric array

Grayscale image, specified as a numeric array. I has the same size, dimensionality and class as X.

Algorithms

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.

Extended Capabilities

Thread-Based Environment

Run code in the background using MATLAB® backgroundPool or accelerate code with Parallel Computing Toolbox™ ThreadPool.

This function fully supports thread-based environments. For more information, see Run MATLAB Functions in Thread-Based Environment.

Version History

Introduced before R2006a

R2021b: Support for thread-based environments

ind2gray now supports thread-based environments.