Summed-area table vs Integral image?

1. What is meant by integral image?
2. What is integral images in image processing?
3. Where is integral image used?

What is meant by integral image?

In an integral image, every pixel is the summation of the pixels above and to the left of it. To illustrate, the following shows and image and its corresponding integral image. The integral image is padded to the left and the top to allow for the calculation.

What is integral images in image processing?

An Integral image is where each pixel represents the cumulative sum of a corresponding input pixel with all pixels above and left of the input pixel. It enables rapid calculation of summations over image sub-regions. Any rectangular subset of such sub-region can be evaluated in constant time.

Where is integral image used?

The Integral Image is one of the most important tools to accelerate features computation in many object detection applications. They are called Summed Area Tables and although they were proposed in 1984 by Frank Crow, it was intensively used within Viola–Jones object detection framework in 2001 [1].