How to use colormap

Question

u-will-neva-no 2012-11-3

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https://ww2.mathworks.cn/matlabcentral/answers/52653-how-to-use-colormap

Hi everyone. I want to color in the letter 'a' from an image full of different characters. I have two images, one with the characters without the letter 'a'(call this A) and one with only the letter 'a'(call this B). I want to set the image B to the color red using colormap but not sure how to use this function in this situation.

Thanks for reading.

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Answer 1

Image Analyst 2012-11-3

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https://ww2.mathworks.cn/matlabcentral/answers/52653-how-to-use-colormap#answer_64177

编辑：Image Analyst 2012-11-3

在 MATLAB Online 中打开

Cast the images to single. Then subtract them and take the absolute value. Then threshold it

subtractedImage  = abs(single(imageA) - single(imageAwithLetter));
binaryImage = subtractedImage > thresholdValue;

Then create image B:

imageB = rgb2gray(imageA);  % or just imageA if imageA is already grayscale.
imageB(imageB == 255) = 254; % Set existing 255 to 254
imageB(binaryImage) = 255; % Set only the letter pixels to 255.
imshow(imageB);
myColormap = gray(256);
myColormap (256,:) = [1 0 0]; % 256 goes to pure red.
colormap(myColormap);
colorbar;