How to know type of image

Question

When I use imread in MATLAB and read an image, how would I know if it is RGB, gray scale or single programmatically?

    I1 = imread('sample_image.jpg');

How can I know what type I1 is before any conversion?

Answer 1

You can use imfinfo to retrieve information about an image file before you load it:

info = imfinfo('sample_image.jpg');
info.ColorType % e.g. 'grayscale', 'truecolor', 'indexed'
info.BitDepth % e.g. 8, 16

You can also look at the help section on imread to see what the output class will be for different file types. The problem comes in determining the difference between a grayscale image, and an indexed colour file - these will have the same size and class. In this case you need to check ColorType beforehand and load the colormap in when you read the image:

[I, map] = imread(filename)