How to display the intensity of 2D image as a colormap?

I have a 2D image. and i want to plot a colormap that represents the intensity of each pixel as a color like the following picture:

I tried to use colormap(image) but it makes error " Error using colormap (line 98)

Colormap must have 3 columns: [R,G,B]."

Does anyone know how to do this in matlab?

[darova]

Do you have intensity of each pixel?

[ghada sandoub]

yes

Answer 1

[Image Analyst]

You need to pass in a colormap, N-by-3 array with values between 0 and 1, to to the colormap() function, NOT an image. And you should probably also pass in a handles to the axes you want to apply it to, otherwise it will apply that colormap to every axes in the figure window, which is probably not what you want. So in short, you want:

myColorMap = hsv(256);      % Create a colormap.
colormap(gca, myColorMap);  % Now apply the colormap. 

You can also pass the colormap directly into imshow() and skip calling the colormap() function if you want.

See this full demo and study it:

grayImage = imread('cameraman.tif');
subplot(3, 1, 1);
imshow(grayImage);
axis('on', 'image');
title('Original Image');

subplot(3, 1, 2);
% Create a colormap.
myColorMap = hsv(256);
% Display image with that colormap.
imshow(grayImage, 'Colormap', myColorMap);
colorbar;
axis('on', 'image');
title('Overlay Image');

% Or equivalently, using the colormap() function:
subplot(3, 1, 3);
% Display image with no colormap.
imshow(grayImage);
% Create a colormap.
myColorMap = hsv(256);
% Now apply the colormap.  Pass in the axes or else it will apply the colormap
% to ALL images on the figure, which is probably not what you want.
colormap(gca, myColorMap);
colorbar;
axis('on', 'image');
title('Overlay Image');

Now, if you already have a colormap, and you want to produce an RGB image, like to write to a file on disk rather than just pseudocoloring a displayed image, you want to call ind2rgb()

rgbImage = ind2rgb(grayImage, myColorMap);

[ghada sandoub]

thanks alot for your help. could you please advise about how to adjust the colormap to represent the intensity from 0 to 1 with colors from blue to red. I tried to use the ( jet mode) to represent the colors from blue to red however the colors ranges from 0 to 4 and I want the colors blue to red to represent from 0 to 1 (blue represents 0 and red represents 1).

[Image Analyst]

Try using jet(256) as the colormap instead of hsv(256).

clc;    % Clear the command window.
fprintf('Beginning to run %s.m.\n', mfilename);
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables. Or clearvars if you want.
clear global;
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 20;

grayImage = imread('cameraman.tif');
subplot(3, 1, 1);
imshow(grayImage);
axis('on', 'image');
title('Original Image');

subplot(3, 1, 2);
% Create a colormap.
myColorMap = jet(256);
% Display image with that colormap.
imshow(grayImage, 'Colormap', myColorMap);
colorbar;
axis('on', 'image');
title('Colormapped Image');

% Or equivalently, using the colormap() function:
subplot(3, 1, 3);
% Display image with no colormap.
imshow(grayImage);
% Create a colormap.
myColorMap = jet(256);
% Now apply the colormap.  Pass in the axes or else it will apply the colormap
% to ALL images on the figure, which is probably not what you want.
colormap(gca, myColorMap);
colorbar;
axis('on', 'image');
title('Colormapped Image');

[ghada sandoub]

yes I already tried using jet instead of hsv however I also need the colors to ranges from 0 to 1 like this:

could you help me to do this?

[Image Analyst]

If your image values go from 0 to 1, it should already do that. Attach your code and image if you still need help.

[ghada sandoub]

I adjusted the color limits to be from 0 to 1 by using : CLim=[0 1] and it works well . Thank you so much.

Answer 2

[Ameer Hamza]

Try this

im = im2double(imread('peacock.jpg'));

im_gray = rgb2gray(im);
pcolor(flipud(im_gray))
shading interp
colormap(jet)
colorbar

You can choose a different colormap from a list here: https://www.mathworks.com/help/releases/R2020a/matlab/ref/colormap.html#buc3wsn-1-map or create your own colormap as an mx3 matrix where each row is an RGB color.

[ghada sandoub]

thanks alot