Technical Reports

The ICICS/CS Reading Room

UBC CS TR-96-06 Summary

Importance Ordering for Real-Time Depth of Field, February 1996 Paul Fearing

Depth of field (DOF) is an important component of real photography. As such, it is a valuable addition to the library of techniques used in photorealistic rendering. Several methods have been proposed for implementing DOF effects. Unfortunately, all existing methods require a great deal of computation. This prohibitive cost has precluded DOF effects from being used with any great regularity.

This paper introduces a new way of computing DOF that is particularly effective for sequences of related frames (animations). It computes the most noticeable DOF effects first, and works on areas of lesser importance only if there is enough time. Areas that do not change between frames are not computed.

All pixels in the image are assigned an importance value. This importance gives priority to pixels that have recently changed in color, depth, or degree of focus. Changes originate from object and light animation, or from variation in the camera's position or focus.

Image pixels are then recomputed in order of importance. At any point, the computation can be interrupted and the results displayed. Varying the interruption point allows a smooth tradeoff between image accuracy and result speed. If enough time is provided, the algorithm generates the exact solution.

Practically, this algorithm avoids the continual recomputing of large numbers of unchanging pixels. This can provide order-of-magnitude speedups in many common animation situations. This increase in speed brings DOF effects into the realm of real-time graphics.

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