The problem is that the output of conv2(I2,G) should be the same size as I2 the way that you have written the code.
In your code above, G, is a scalar, so you have constructed a for loop:
for ii=1:m
for jj =1:n
J(ii,jj)=conv2(I2,G);
end
end
that is convolving a matrix with a scalar.
For example:
G = 2;
x = randn(10,10);
size(conv2(x,G))
You cannot then assign this result to J(ii,jj). For example:
J(1,1) = conv2(x,G);
throws the error you are getting for the reasons I explained.
