Comparing two different images seems to fail

[thathurtabit]

Hi, my apologies if this is related to #195

On the demo site, when comparing two images (I've tried both jpegs and pngs) with no overlap, it only states:
"The second image is 20.44% different compared to the first."
Whereas I would imagine it should be 100% different?

Output:

Input 1:

Input 2:

[gaitat]

I would assume the comparison percentage comes from the total number of pixels that are different. Your images have a lot of white pixels which are not computed as different.

[jamescryer]

The pink pixels in the diff are 20.44% of the total diff image, even though the source images are literally 100% different.