MATLAB: How to use function ‘ind2gray’

colormaperrorImage Processing Toolboxind2gray

I'm trying to convert uint8 image to grayscale image using the following command

a = imread('image.png'); % a dimension 18*24*3
b = ind2gray(a, map);

But I'm getting an error message saying

Undefined function or variable 'map'

Best Answer

You need to have some way to tell the function what color should get mapped to what gray level. The colors are a 2D array with columns for red green, and blue in the range 0-1, and one row for each gray level or range of gray levels. There are several built-in color maps to select from - see the help for colormap. For example you could do

rgbImage = ind2rgb(grayImage, jet(256));
colorbar;

jet() is a function that builds a colormap of a certain pattern with the number of gray levels you specify. There are others too. Or you could make up your own colormap completely customized.

Related Solutions

MATLAB: Assigning color to gray image

I'd just use colormap and not mess with contours unless you know what you're doing and what you want. To pseudocolor a grayscale image an leave it as grayscale but display it as colored:

imshow(grayImage);
colormap(jet(256));
colorbar;

To convert a grayscale image into a true color RGB image and display the RGB image instead of the pseudocolored image:

rgbImage = ind2rgb(grayImage, jet(256));
imshow(rgbImage);

You don't use color bars with RGB images.

MATLAB: Read and display RGB png/jpg image

You png file is actually an indexed image with a colormap. You can see it in color using following statements

[img, map] = imread('image.png');
imshow(img, map)

or, you convert it to rgb, you can use ind2rgb()

[img, map] = imread('image.png');
img_rgb = ind2rgb(img, map);
imshow(img_rgb)

Best Answer

Related Solutions

MATLAB: Assigning color to gray image

MATLAB: Read and display RGB png/jpg image

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