MATLAB: How to convert gray or indexed images to color images

colormapconvertImage Processing Toolboxindexed image

Hi. I applied The following code to resize my images. The input images are color images. But as an output, the resized images are gray! How do I correct it?

Best Answer

That image is a 2D image, an indexed image with a color map. It's not a 3D color RGB image. You need to convert it to an RGB image if you recognize it's an indexed image. Replace your loop with this:
for k = 1:numel(bmpFiles)
  fullInputFileName = fullfile(inputFolder,bmpFiles(k).name)
  [originalImage, colorMap] = imread(fullInputFileName);
  [rows, columns, numberOfColorChannels] = size(originalImage)
  if ~isempty(colorMap) && numberOfColorChannels == 1
    % It's an indexed image with a colormap.
    % Convert it to RGB color
    originalImage = ind2rgb(originalImage, colorMap);
    [rows, columns, numberOfColorChannels] = size(originalImage)
  end
  fullOutputFileName = fullfile(outputFolder, bmpFiles(k).name);
  outputImage = imresize(originalImage, [100,50]);
  [rows columns numberOfColorChannels] = size(outputImage);
  if numberOfColorChannels == 1
    % It's monochrome, so convert to color.
    outputImage = cat(3, outputImage, outputImage, outputImage);
  end
  
  figure,imshow(outputImage);
  imwrite(outputImage, fullOutputFileName);
end
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