psnr.m

分数阶傅里叶变换在数字水印中的一个应用

function PSNR(A,B)

% PURPOSE: To find the PSNR (peak signal-to-noise ratio) between two
%          intensity images A and B, each having values in the interval
%          [0,1]. The answer is in decibels (dB).
%
% SYNOPSIS: PSNR(A,B)
%
% DESCRIPTION: The following is quoted from "Fractal Image Compression",
%              by Yuval Fisher et al.,(Springer Verlag, 1995),
%              section 2.4, "Pixelized Data".
%
%              "...PSNR is used to measure the difference between two
%              images. It is defined as
%
%                           PSNR = 20 * log10(b/rms)
%
%              where b is the largest possible value of the signal
%              (typically 255 or 1), and rms is the root mean square
%              difference between two images. The PSNR is given in
%              decibel units (dB), which measure the ratio of the peak 
%              signal and the difference between two images. An increase
%              of 20 dB corresponds to a ten-fold decrease in the rms
%              difference between two images.
%              
%              There are many versions of signal-to-noise ratios, but
%              the PSNR is very common in image processing, probably
%              because it gives better-sounding numbers than other
%              measures."
%
% EXAMPLE 1: load clown
%            A = ind2gray(X,map); % Convert to an intensity image in [0,1].
%            B = 0.95 * A;        % Make B close to, but different from, A.
%            PSNR(A,B)            % ---> "PSNR = +33.49 dB"
%
% EXAMPLE 2: A = rand(256); % A is a random 256 X 256 matrix in [0,1].
%            B = 0.9 * A;   % Make B close to, but different from, A.
%            PSNR(A,B)      % ---> "PSNR = +24.76 dB (approx)"

if A == B
   error('Images are identical: PSNR has infinite value')
end

max2_A = max(max(A));
max2_B = max(max(B));
min2_A = min(min(A));
min2_B = min(min(B));

if max2_A > 1 | max2_B > 1 | min2_A < 0 | min2_B < 0
   error('input matrices must have values in the interval [0,1]')
end

err = A - B;
decibels = 20*log10(1/(sqrt(mean(mean(err.^2)))));
disp(sprintf('PSNR = +%5.2f dB',decibels))