Alex:
If you want a double, you can use double() on an image. Or im2double().
If you want a gray scale image, you can either call rgb2gray() or take one of the color channels
rgbImage = imread(fullFileName);
[rows, columns, numberOfColorChannels] = size(rgbImage)
if numberOfColorChannels == 3
grayImage = rgb2gray(rgbImage); % Method 1
grayImage = rgbImage(:, :, 1); % Method 2 take red channel
else
grayImage = rgbImage; % It's already gray scale
end
Once you've thrown away color information, you can't get it back. If you need it, be sure to save your original RGB image or read it back in from disk.
If you want your double image to be back in uint8 format you can pass it in to uint8. If it's not in the same range as uint8 you need to decide how to scale it. You can either divide by the max and multiply by 255
gray8 = uint8(255 * grayImage / max(grayImage(:));
or you can scale the min to zero and the max to 1 with mat2gray() or rescale():
gray8 = uint8(255 * mat2gray(grayImage)); % Method 1
gray8 = uint8(rescale(grayImage, 0, 255)); % Method 2
You can convert a gray scale image into a gray scale RGB image by concatenating your gray scale image so that it is in every color channel. It will be a 3-D RGB image though it will look gray.
rgbImage2 = cat(3, grayImage, grayImage, grayImage);
You could also use ind2rgb() if you want
rgbImage2 = ind2rgb(grayImage, yourColorMap);
