creating a custom color map
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I'm looking to create a custom color map so that an image appears as various shades of red. I understand that this would require changing the matrix of the RGB image to an image consisting of _,0,0, but I am not sure of the best way to go about this
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Image Analyst
on 25 Feb 2015
You don't need an RGB image. In fact RGB images don't even take a colormap. If you want an RGB image, just create one
rgbImage = cat(3, grayImage, zeros(size(grayImage), 'uint8'), zeros(size(grayImage), 'uint8'));
imshow(rgbImage);
Or use a colormap with your grayscale image:
grayImage = imread('moon.tif');
imshow(grayImage);
colorMap = [linspace(0,1,256)', zeros(256,2)]
colormap(colorMap);
colorbar;
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/173529/image.jpeg)
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Image Analyst
on 5 May 2020
Try this:
yellowMap = [linspace(0, 255, 256)', linspace(0, 255, 256)', zeros(256, 1)]
colormap(yellowMap);
DGM
on 16 Jan 2023
I'm not so sure that's a simple false color image. It may be a composite. That possibility aside, here's a better approximation:
% reduced sampling
x0 = [0 0.008889 0.03556 0.08 0.1422 0.2222 0.32 0.4356 0.5644 0.68 0.7778 0.8578 0.92 0.9644 0.9911 1];
CT0 = [0 0 0.1; 0.002914 0.01103 0.1143; 0.01221 0.02996 0.1352; 0.02938 0.04745 0.1489; 0.05622 0.07057 0.1604; ...
0.09753 0.1003 0.1803; 0.1756 0.1568 0.2046; 0.2908 0.2456 0.2395; 0.4299 0.355 0.2906; 0.5757 0.4753 0.3516; ...
0.7288 0.6116 0.427; 0.8555 0.7448 0.5124; 0.9486 0.8541 0.6076; 0.9871 0.9329 0.7081; 0.9983 0.983 0.809; 1 1 0.95];
% generate a new uniform table of desired length
N = 256;
xf = linspace(0,1,N);
CT = interp1(x0,CT0,xf,'pchip');
% use the map to plot something
x = linspace(-pi/2,pi/2,30);
y = x.';
z = sin(x).*sin(y);
surf(x,y,z)
colormap(CT)
colorbar
view(-17,50)
Of course, the dark blue is essentially black against this awful white background, but that's what you get.
Note that even though we might be able to define some trajectory through some color space, there's no information which unambiguously informs us about the rate at which that path is traversed with respect to the mapped variable. Here, we're assuming it's linear.
% generate some example images using shifted versions of the CT
testsweeps = cat(3,ctshift(CT,-0.67), ...
ctshift(CT,-0.33), ...
ctshift(CT,0), ...
ctshift(CT,0.33), ...
ctshift(CT,0.67));
testsweeps = permute(testsweeps,[3 1 2]);
testsweeps = imresize(testsweeps,[128 256],'nearest');
imshow(testsweeps)
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/1265040/image.png)
Alka Nair
on 25 Feb 2015
Edited: per isakson
on 25 Feb 2015
The 'colormapeditor' helps in displaying the current figure's colormap and customizing it. To find more information about colormapeditor, please refer to the documentation at:
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