Anti-aliasing with Stratified B-spline Filters

Manuel N. Gamito

Steve C. Maddock

The University of Sheffield

A simple and elegant method is presented to perform anti-aliasing in ray traced images. The method uses stratified sampling to reduce the occurrence of artifacts in an image and features a B-spline filter to compute the final luminous intensity at each pixel. The method is scalable through the specification of the filter order. A B-spline filter of order one amounts to a simple anti-aliasing scheme with box filtering. Increasing the order of the B-spline generates progressively smoother filters. Computation of the filter values is done in a recursive way, as part of a sequence of Newton-Raphson iterations, to obtain the optimal sample positions in screen space. The proposed method can perform both anti-aliasing in space and in time, the latter being more commonly known as motion blur. We show an application of the method to the ray casting of implicit procedural surfaces.

This paper was initially written as technical report CS-05-02 for the Department of Computer Science, The University of Sheffield. It was later extended to include anti-aliasing in time and was published in the June 2006 number of the Computer Graphics Forum journal. The final paper is available at www.blackwell-synergy.com. A draft version of the paper is available below:

PDF format (347 K) (bsplinecgf.pdf)

Some Animations from the Paper

Here are a couple of animations using the anti-aliasing method presented in the paper. They can be visualised as an infinite cycle by turning on looping in the movie viewer.

	An animation of a complex rotating iso-surface comparing rendering with no anti-aliasing (on the left) with rendering with anti-aliasing in both space and time (on the right). Quicktime MOV format (11.8M) (isosurf.mov)
	An animation demonstrating anti-aliasing in time with the famous wagon wheel illusion. The spokes on the wheel are turning counter-clockwise at high speed but the blurred features in the animation slowly turn clockwise. In this sequence, we compare anti-aliasing in time as performed by a camera shutter and a cubic B-spline filter. Quicktime MOV format (11.4M) (wagonwheel.mov)