negetive valu for PSNR after image enhancment in MATLAB

Hi, after image enhancement in frequency domain for assessment calculate psnr and value of psnr and snr is negative. class of input and output image is double.

 ref = imread('img.tif');
 ref=im2double(ref);
 %A = processing(ref);
 %Calculate the PSNR.
 [peaksnr, snr] = psnr(A, ref);

please guide me about valu of PSNR.

Answer 1

[Image Analyst]

What is A??? And you forgot to attach img.tif and the "A" image, so I'm not going to do anything yet.

Since

PSNR=10log10(peakval^2/MSE)

and since you can't have negative values of PSNR unless MSE < peakValue^2, you must have A and ref on different scales, like you called im2double on one but not the other.

[fred bnm]

"ref" convert to double for frequency filtering.

[Image Analyst]

Yes, but im2double() scaled the data to between 0 and 1. Did you also do that for A? I'm thinking not otherwise the SNR would not be negative.