Integral images, also known as summed area tables, are another form of storing images. For integral images, we replace each pixel in the image with the sum of all the elements on the left and above that pixel.

The formula shown next is used to compute integral images:

Where, *i(x', y')* means the value of pixel at *(x', y')* in the image. *I *is the **integral image**.

If we closely look at the formula for calculating integral images, we will notice that there are a lot of redundant calculations that we make. For computing the value for pixel (5, 5), we compute the value for pixel (1, 1), (2, 2), and so forth. We can avoid these calculations ...