Hi all...i am writing a code to calculate the PSNR of two images....but i am getting an error as 'Attempted to access A1(1,401); index out of bounds because size(A1)=[​400,400].'​..Here A1 is the R component of image.. The code is shown below

clc;
close all;
clear all;

A = imread('F:\EXPERIMENTION RESULTS\fruits_ORIGINAL.jpg');
A = imresize(A ,[400 400]);
A = double(A);

A1 = A(:,:,1);
A2 = A(:,:,2);
A3 = A(:,:,3);

B = imread('F:\EXPERIMENTION RESULTS\fruits_HISTEQ.jpg');
B = imresize(B , [400 400]);
B = double(B);

B1 = B(:,:,1);
B2 = B(:,:,2);
B3 = B(:,:,3);

[m n] = size(A);
[m2 n2] = size(B);
if m ~= m2 || n ~= n2 
    error('sizes do not match')
end

msevalue1 = 0;
for i = 1:m
    for j = 1:n
        msevalue1 = msevalue1 + ((A1(i,j) - B1(i,j)))^2;
    end
end
msevalue1 = msevalue1/(m*n);
if msevalue1 == 0
    error ('verify the image correctly')
end

signalval1 = 0;
for i = i:m
    for j = 1:n
        signalval1 = signalval1 + (A1(i,j))^2;
    end
end
signalval1 = signalval1/(m*n);
snrval1 = signalval1/msevalue1;
snrvalue1 = 10*log10(snrval1);
psnrvalue1 = 255^2/msevalue1;
psnrvalue1 = 10*log10(psnrvalue1);

msevalue2 = 0;
for i = 1:m
    for j = 1:n
        msevalue1 = msevalue1 + ((A2(i,j) - B2(i,j)))^2;
    end
end
msevalue2 = msevalue2/(m*n);
if msevalue2 == 0
    error ('verify the image correctly')
end

signalval2 = 0;
for i = i:m
    for j = 1:n
        signalval2 = signalval2 + (A2(i,j))^2;
    end
end
signalval2 = signalval2/(m*n);
snrval2 = signalval2/msevalue2;
snrvalue2 = 10*log10(snrval2);
psnrvalue2 = 255^2/msevalue2;
psnrvalue2 = 10*log10(psnrvalue2);

msevalue3 = 0;
for i = 1:m
    for j = 1:n
        msevalue3 = msevalue3 + ((A1(i,j) - B1(i,j)))^2;
    end
end
msevalue3 = msevalue3/(m*n);
if msevalue3 == 0
    error ('verify the image correctly')
end

signalval3 = 0;
for i = i:m
    for j = 1:n
        signalval3 = signalval3 + (A3(i,j))^2;
    end
end
signalval3 = signalval3/(m*n);
snrval3 = signalval3/msevalue3;
snrvalue3 = 10*log10(snrval3);
psnrvalue3 = 255^2/msevalue3;
psnrvalue3 = 10*log10(psnrvalue3);

psnr=(psnrvalue1+psnrvalue2+psnrvalue3)/3

Answer 1

[Image Analyst]

psnr() was introduced in the R2014a Image Processing Toolbox. I suggest you use that. Or you can use my attached demo.

The reason for your error is that you can't do this:

[m n] = size(A);
[m2 n2] = size(B);

because A and B are color images. You need to do this:

[m, n, numberOfColorChannels] = size(A);
[m2, n2, numberOfColorChannels2] = size(B);

If you don't then n and n2 are multiplied by 3. Why? See http://blogs.mathworks.com/steve/2011/03/22/too-much-information-about-the-size-function/

[Star Strider]

There’s also a PSNR function on the File Exchange. Don’t have any experience with it myself.

Answer 2

[Geoff Hayes]

Please edit the above code so that it readable - use the {}Code button to do so.

One thing I noticed is that for a couple of your outer for loops, you are iterating using the variable i starting from i and ending at m (which is 400). This should be fixed (unless done on purpose?).

The problem is with determining the number of rows and columns for matrices A1,A2,A3:

[m n] = size(A);

A is three dimensional and so is of size 400x400x3. In the above code, if you supply only two outputs ( m and n) for a three dimensional matrix, then m=400 (as expected) but n=1200 which is the product of the last two dimensions (400*3). This behaviour is documented in the size command help info (type help size at the command window for details). And this explains the error that is being raised as j iterates from 1 to 1200 ( n ) and so fails at j==401.

Since you are using m and n to access the elements of the A1,A2, and A3 matrices - all three of which are the same size - then just replace the above with:

[m,n] = size(A1);

The same error exists for m2 and n2.