Calculating the RMSE value between two images

I calculated the RMSE value between two images of size 128 x 128 in .jpg format and I am getting the result above 1. I want the range to be between 0-1. I tried applying imadjust to normalize but it did not help. How can I normalize the image and get the required result between 0-1. I also tried to save the images in .mat file and normalize it but I am getting error as the image is being saved as type struct and not double. Please help.Thank you in advance.

I used the following line to calculate rmse:

rmse_val = sqrt(mean((ref(:)-a(:)).^2))

Answer 1

[Image Analyst]

You forgot to attach your variables. I don't know if you can subtract structures like that so I think ref and (the badly-named) a are actually numerical arrays, not structures. If they are uint8 gray scale images, you should convert to double before subtracting, and use the rms function:

a = imread('cameraman.tif');
ref = a + 10;
% First method is to use rms on the difference array.
diffImage = double(ref) - double(a);
r = rms(diffImage(:))

r = 9.9975

% Alternate way is to use rmse
re = rmse(double(ref(:)), double(a(:)))

re = 9.9975

[Shourya]

@Image Analyst Thank you for the solution and explaination.Thank you for pointing out the variables details. Sorry I missed them. The groundtruth image is referred to as 'ref' and the test image is referred to as 'a'. Yes, they are uint8 gray scale images. I tried the above solution but I get the result as 5.69. I want it between 0-1 or how can I get the result in precentage.

[Image Analyst]

You can divide either by the max value in your reference image, or divide by 255, depending on how you define percentage.

[Shourya]

This is what I will get 5.69/255=0.0219. Is this right?

[Image Analyst]

Yes