function snr = SNR(I,In)
I = imread('pout.tif');
In = imnoise(I,'salt & pepper',0.5);
% 计算信号噪声比函数
% by Qulei
% I
riginal signal
% In:noisy signal(ie. original signal + noise signal)
% snr=10*log10(sigma2(I2)/sigma2(I2-I1))
[row,col,nchannel] = size(I);
snr = 0;
if nchannel == 1%gray image
Ps=sum(sum((I-mean(mean(I))).^2));%signal power
Pn=sum(sum((I-In).^2));%noise power
snr=10*log10(Ps/Pn);
elseif nchannel==3%color image
for i=1:3
Ps=sum(sum((I(:,:,i)-mean(mean(I(:,:,i)))).^2));%signal power
Pn=sum(sum((I(:,:,i)-In(:,:,i)).^2));%noise power
snr=snr+10*log10(Ps/Pn);
end
snr=snr/3;
end