Asked by akanksha sharma
on 4 Oct 2012

I have to compare image compression techniques like VQ, JPEG, WAVELET, and fractal. For this, the parameter to be compared is PSNR. Please tell me how I can calculate PSNR OF AN IMAGE which is COMPRESSED by different compression techniques. plz explain with example.

Answer by Image Analyst
on 4 Oct 2012

Edited by Image Analyst
on 4 Oct 2012

See my demo:

% Demo to calculate PSNR of a gray scale image. % http://en.wikipedia.org/wiki/PSNR % Clean up. close all; clear all; workspace;

%------ GET DEMO IMAGES ---------------------------------------------------------- % Read in a standard MATLAB gray scale demo image. grayImage = imread('cameraman.tif'); [rows columns] = size(grayImage);

% Display the first image. subplot(2, 2, 1); imshow(grayImage, []); title('Original Gray Scale Image'); set(gcf, 'Position', get(0,'Screensize')); % Maximize figure.

% Get a second image by adding noise to the first image. noisyImage = imnoise(grayImage, 'gaussian', 0, 0.003);

% Display the second image. subplot(2, 2, 2); imshow(noisyImage, []); title('Noisy Image');

%------ PSNR CALCULATION ---------------------------------------------------------- % Now we have our two images and we can calculate the PSNR. % First, calculate the "square error" image. % Make sure they're cast to floating point so that we can get negative differences. % Otherwise two uint8's that should subtract to give a negative number % would get clipped to zero and not be negative. squaredErrorImage = (double(grayImage) - double(noisyImage)) .^ 2; % Display the squared error image. subplot(2, 2, 3); imshow(squaredErrorImage, []); title('Squared Error Image'); % Sum the Squared Image and divide by the number of elements % to get the Mean Squared Error. It will be a scalar (a single number). mse = sum(sum(squaredErrorImage)) / (rows * columns); % Calculate PSNR (Peak Signal to Noise Ratio) from the MSE according to the formula. PSNR = 10 * log10( 256^2 / mse); % Alert user of the answer. message = sprintf('The mean square error is %.2f.\nThe PSNR = %.2f', mse, PSNR); msgbox(message);

Show 2 older comments

Image Analyst
on 12 Oct 2013

Karbala'a Unvi. Science
on 20 Feb 2015

Said BOUREZG
on 20 Feb 2015

Image Analyst have do all thing, nothing to say it after this answer, thank you sir for this code.

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