function dPSNR = psnr(imA,imB,iMax)
%% -------------------------------------------------------------------- %%
% Function: Calculates the PSNR (Peak Signal to Noise Ratio)
%     From: 
% Argument: dPSNR: PSNR
%           imA: ImageA
%           imB: ImageB
%           MaxGray: 理论应为max(max(imA),max(imB))
%     Demo: psnr(imA,imB);
%  Version: 2.01.20090510,1.07.20061215
%    Email: weiweimin@hotmail.com
%      Web: http://www.TrueMark.cn
%% -------------------------------------------------------------------- %%
dPSNR = 0;
% 参数预处理
if( ~exist('imA') )
    imA = loadimg();
end
if isempty(imA); return; end;

if( ~exist('imB') )
    imB = loadimg();
end
if isempty(imB); return; end;

% 格式转换
imA = double(imA);
imB = double(imB);

% MaxGray一般应为max(max(imA),max(imB))
if( ~exist('iMax') )
    iMax = max(max(imA(:)),max(imB(:)));
%     iMax = 255;
end

% 判断两个图像是否匹配
if (size(imA) ~= size(imB))
    error('Images must be the same size.');
    return;
end
% 判断两个图像是否完全一样
if imA == imB
   error('Images are identical: PSNR has infinite value.');
   return;
end

[iH iW iL] = size(imA); % iH=Height,iW=Width

% 如果是彩色则取三个通道的均值
dMSE = sum(abs((imA(:) - imB(:))).^2)/iL + eps;
dPSNR = 10*log10((iH*iW*(iMax^2))/dMSE);

disp(['PSNR = ',num2str(dPSNR,'%5.2f dB')]);
%% -------------------------------------------------------------------- %%