How to compare or find out the P.S.N.R. value of two images?

I am giving two images below can anybody help in finding out the P.S.N.R. value of them? My base picture is "t.png" and the image after processing is "output.png", can anybody help me in finding out their respective P.S.N.R. values?

Answer 1

[Image Analyst]

Copied from the help:

psnr

Peak Signal-to-Noise Ratio (PSNR) expand all in page
Syntax
peaksnr = psnr(A,ref) example
peaksnr = psnr(A,ref,peakval)
[peaksnr,snr] = psnr(___)
Description
example
peaksnr = psnr(A,ref) calculates the peak signal-to-noise ratio for the image A, with the image ref as the reference. A and ref must be of the same size and class.

peaksnr = psnr(A,ref,peakval) uses peakval as the peak signal value for calculating the peak signal-to-noise ratio for image A.

[peaksnr,snr] = psnr(___) returns the simple signal-to-noise ratio, snr, in addition to the peak signal-to-noise ratio.

[Sandeep V]

 peaksnr = Psnr('t.png','output.png')
Error using  == 
Matrix dimensions must agree.

Error in Psnr (line 15) elseif (A == B) but my matrix dimensions are same 512*384 and class is unit8

[Image Analyst]

I said psnr, not Psnr. MATLAB is case sensitive.

[Sandeep V]

I have to compare o.png and output1.png and I am getting error

A=imread('output1.png');
>> B=imread('o.png');
>> peaksnr = psnr(A,B) 
??? Undefined function or method 'psnr' for input arguments of type 'uint8'.
A=<540x960x3 uint8>
B=<540x960x3 uint8>

Can you just compare o.png and output1.png and check whether you are getting any result?

[Image Analyst]

You must have an old version of MATLAB. See my attached psnr demo that does not use the built-in psnr() function. I'm not sure if it handles color images. If it doesn't then you'll have to do one color channel at a time.

[Sandeep V]

Your code is working for my colored image.I made some changes and I am getting PSNR as 28.28. Instead of adding noise, I made the second image the base image(the one I want to compare with), does the PSNR give any indication that the image is better than the base one?

[Image Analyst]

No. The PSNR does not tell you which image is "better". It tells you how close your image is to the reference image, but not which is a better image (like less noisy or more vivid colors or whatever).

[Atif Anwer]

@Image Analyst:

Apologies for replying to an old question; but with reference to the psnr.m file provided by you since you are type casting the pixel values to double, shouldnt the 'peakvalue' term in the PSNR be 65535^2 insted of 256^2 (which would be for the uint8 image)? Or even 1 since, double image values range between 0-1

Sorry again for revivng an old question but i think this needs a little calrification.

[Image Analyst]

Yes, for am 8 bit image use 255, for a 16 bit image use 65,535, and for a floating point image, use 1.

[MD IS]

@Image Analyst

I appreciated your answer 'The PSNR does not tell you which image is "better". It tells you how close your image is to the reference image'.

Which value (low or high) of PSNR tell me about my image is closer to the reference image. I am a little bit confused about the value of PSNR; hence looking for an anwer from you. Thank you.

Answer 2

[VISHNU MENON]

can we have reference image as bmp format whereas other image as jpg format and perform the psnr. should both be of same format?

[Image Analyst]

Of course. The format on disk doesn't matter. Once they're read into memory in your program, they're all the same, like an RGB image or a gray scale image, and the disk format doesn't matter.