I want to find similarity between two images.I use SSIM. What does low and high values of SSIM indicates in terms of similarity.

I want to find similarity between two images.I use SSIM. What does low and high values of SSIM indicates in terms of similarity.

[Asim Maqsood]

And what does it mean if we have a negative answer like -0.5 or -1?

[Image Analyst]

From the formula in the help, it looks like the only way you could get a negative number is if one of the images has a negative mean value.

Answer 1

[Image Analyst]

If you open the example script from the help, and change this line:

[ssimval, ssimmap] = ssim(A,ref);

to

[ssimval, ssimmap] = ssim(ref,ref);

you'll see that the ssim goes from 0.94 to 1.00, showing that if the images are exactly the same, the ssim is 1 and the more different they are, the lower the ssim value, down to as far as zero.