how to compare similarity of two color images of different sizes?

The metrics like psnr and ssim can be used if the reference images are of same size. So how to compare the similarity of two color images of different sizes?

Answer 1

[Sulaymon Eshkabilov]

This question is quite obscure. Similarity of the images can be checked in terms of average of pixel values (color intersity), and color spaces (CIElab) and HSV. There are several built-in fcns in image processing toolbox that can be employed with this question, e.g.: mean2(), rgb2lab(), rgb2hsv(), etc.