please explain size function in MATLAB

if(size(img,3) == 1) disp('Error: Pick a color image'); return;

Answer 1

[Image Analyst]

size(img,3) returns the number of color channels in an image. It will be 1 for a gray scale image and 3 for an RGB image. That should explain it (why they ask for a color image if the program was given a gray scale image).