We found blob detection a bit too complex and finicky for our application, so we opted for a much simpler approach—we create a five frame buffer and compared the difference between the first and last grayscale images. The bigger the difference between the two images, the higher the number of white pixels. We used the percentage of white pixels in the resulting image to compute a number that would control the phase of a gradient ramp. The the more white pixels, the more motion, the higher the ramp shifted toward red.

Here is a link to our TouchDesigner file: https://cmu.box.com/s/kmmqwe2gr25yi8iixizsvoc0abyn19da