This a online javascript implementation of Freeman and Adelson’s separable steerable filter. It has a quadrature filter bank and, by using the steering equations, the filter can be steered to a given orientation. In this case a magnitude/orientation image is created from a webcam image (orientation is represented as hue). I won’t reproduce the javascript code here as it is too lengthy (can easily be seen in the browser debug window), I also won’t describe the technique as the seminal paper below does a much better job of explaining the science behind the steerable filter.
W. T. Freeman and E. H. Adelson, The design and use of steerable filters, IEEE Trans. on Pattern Analysis and Machine Intelligence, vol. 13, no. 9, pp. 891 – 906, September, 1991. MIT Vision and Modeling Group TR 126.
You can also see a prtical example of the use of steerable filter for classifying protein crystallography images and an example of a multi-resolution (in terms of 2D spatial frequency) steerable pyramid image that I made of Marilyn Monroe using the same original image that Andy Warhol used for his popart paintings.
This app has now been modified to work with HTML5 video instead of flash, much better!