MATLAB: My image is RGB image but when I used size function it showed me grayscale image.

digital image processingimage processingMATLABmatlab function

I have an image. When I open it using windows photo viewer it showed RGB image but when I use size function of Matlab for finding color channel it showed me "1". That's mean it is the grayscale image. The image also attached.

My Matlab code is:

[rows, columns, numberOfColorChannels] = size('test.jpg');

Output is: numberOfColorChannels is "1"

Best Answer

There is no problem, you just did not actually read the image into MATLAB. It works perfectly for me:

>> [img,map] = imread('test.jpg');
>> size(img)
ans =
    96   200     3

Or alternatively:

>> S = imfinfo('test.jpg');
>> S.ColorType
ans = truecolor

Nope, not a grayscale image at all.

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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: How to check for a RGB image or Grayscale image before execution

See this snippet where I check if the number of color channels is 1 and then, if it's not, and I wanted a grayscale image instead of an RGB image, I convert it to gray scale:

grayImage = imread(fullFileName);
% Get the dimensions of the image.  
% numberOfColorBands should be = 1.
[rows, columns, numberOfColorChannels] = size(grayImage);
if numberOfColorChannels > 1
  % It's not really gray scale like we expected - it's color.
  % Convert it to gray scale by taking only the green channel.
  grayImage = grayImage(:, :, 2); % Take green channel.
end

Of course you can call the image array anything you want, and check if numberOfColorChannels > 1 or if numberOfColorChannels == 3, or however you want to do it, and then take whatever actions you want to based on knowing how many color channels it has.

Best Answer

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MATLAB: Assigning color to gray image

MATLAB: How to check for a RGB image or Grayscale image before execution

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