Matlab imread return 4 channel matrix

Question

I do imread image in Matlab, and it returns a 4-channel image:

im: 1012x972x4 uint8.

Which format is this image? How to check its color format(RGB, CMYK, etc)? I opened it in Gimp and the color profile is simply sRGB built-in

Answer 1

From imread() documentation :

The return value A is an array containing the image data. If the file contains a grayscale image, A is an M-by-N array. If the file contains a truecolor image, A is an M-by-N-by-3 array. For TIFF files containing color images that use the CMYK color space, A is an M-by-N-by-4 array. See TIFF in the Format-Specific Information section for more information.

So the answer is apparently that this image's color space is CMYK.

If you want to check for a general input, then, from the same page:

To determine which color space is used, use imfinfo to get information about the graphics file and look at the value of the PhotometricInterpretation field.