What does it mean to get the (MSE) mean error squared for 2 images?

image, image-processing, imagemagick, opencv

Solution

For two pictures A, B you take the square of the difference between every pixel in A and the corresponding pixel in B, sum that up and divide it by the number of pixels.

Pseudo code:

sum = 0.0
for(x = 0; x < width;++x){
   for(y = 0; y < height; ++y){
      difference = (A[x,y] - B[x,y])
      sum = sum + difference*difference
   }
}
mse = sum /(width*height)
printf("The mean square error is %f\n",mse)

Problem

The MSE is the average of the channel error squared. What does that mean in comparing two same size images?

Original source