Why my value of MSE and PSNR have 3 values?

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Atifah Samuri 2021-12-30

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https://ww2.mathworks.cn/matlabcentral/answers/1619935-why-my-value-of-mse-and-psnr-have-3-values

编辑： DGM 2021-12-31

采纳的回答： DGM

My code is shown below:

InputImage=imread('ifa.jpg');

ReconstructedImage=imread('ifamedifilt.jpg');

n=size(InputImage);

M=n(1);

N=n(2);

MSE = sum(sum((InputImage-ReconstructedImage).^2))/(M*N);

PSNR = 10*log10(256*256/MSE);

fprintf('\nMSE: %7.2f ', MSE);

fprintf('\nPSNR: %9.7f dB', PSNR);

and these are the values:

MSE: 0.88

MSE: 7.45

MSE: 1.94

PSNR: 48.7440467 dB

PSNR: 39.4403644 dB

PSNR: 45.2839345 dB

First image is ifa.jpg and the next one is ifamedifilt.jpg

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Answer 1

DGM 2021-12-31

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https://ww2.mathworks.cn/matlabcentral/answers/1619935-why-my-value-of-mse-and-psnr-have-3-values#answer_865430

编辑：DGM 2021-12-31

在 MATLAB Online 中打开

The images are RGB. The results are 1x1x3 -- one result per channel.

If your goal were to get a single value for the whole image, you can do that.

MSE = sum((InputImage(:)-ReconstructedImage(:)).^2)/(M*N);

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Atifah Samuri 2021-12-31

The images in RGB and the value have 3. If I use this code:

MSE = sum((InputImage(:)-ReconstructedImage(:)).^2)/(M*N);

Which value is used to get a single value?

How it operate?

DGM 2021-12-31

编辑：DGM 2021-12-31

在 MATLAB Online 中打开

That's taking the MSE of all elements of the array when compared to the corresponding element in the other array. It does it by reshaping the arrays into vectors. You could do the same thing by doing

MSE = sum((InputImage-ReconstructedImage).^2,'all')/(M*N);

Either way, the point is to reduce the numerator to a scalar. It's not picking one particular channel, nor is it converting to grayscale. An error in the blue channel has the same weight as an error in red or green, which is not the case when doing luma conversion with rgb2gray(). It all depends what's desired.

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Answer 2

yanqi liu 2021-12-31

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https://ww2.mathworks.cn/matlabcentral/answers/1619935-why-my-value-of-mse-and-psnr-have-3-values#answer_865455

编辑：yanqi liu 2021-12-31

在 MATLAB Online 中打开

yes，sir，it is rgb type，may be use rgb2gray to make it gray type，such as

InputImage=double(rgb2gray(imread('https://www.mathworks.com/matlabcentral/answers/uploaded_files/848510/image.jpeg')));
ReconstructedImage=double(rgb2gray(imread('https://www.mathworks.com/matlabcentral/answers/uploaded_files/848515/image.jpeg')));
n=size(InputImage);
M=n(1);
N=n(2);
MSE = sum(sum((InputImage-ReconstructedImage).^2))/(M*N);
PSNR = 10*log10(256*256/MSE);
fprintf('\nMSE: %7.2f ', MSE);
MSE:    2.48 
fprintf('\nPSNR: %9.7f dB', PSNR);
PSNR: 44.2200271 dB