imagemagick compare -metric rmse result interpretation

Question

i did the following to get difference between two png files:

 compare -metric rmse a.png b.png null:

result i got is:

 3374.35 (0.0514893)

i am running it on windows. Can you please tell me what those numbers mean? Does the b.png deviates too much from a.png? Can you give me link, if possible, where I can read on results explanations? thanks in advance!!!

Answer 1

Seems it calculates RMSE on (RGB.a-RGB.b) values. The lower first number - the more similar images are. But the interpretation of similarity depends on image sizes you are trying to compare. Second number may be probability that any pixel will be different between a and b versions of it. But I'm not sure.

A bit about -metric options documentation.