The integral image was introduced
to the image processing community by Viola and Jones^{[3]}
similar to summed area tables in texture mapping^{[1]},
it gives a fast way to calculate block features in an image.
We, along with others^{[4]},
have taken this into the temporal domain, in a video stream one
can imagine the images stacked one behind the other in temporal
order. To create a space time integral any point (x,y,z) now contains
the sum of all points to its upper left plus those before it as
shown in figure 1. Now to calculate a block summation four subtractions
and three additions are required, regardless of the block size.


figure 1  The value of the integral volume point (x,y,z)
is the sum of all the points in the current and previous frames
to the upper left of itself 
