Flexible Depth of Field Photography

by H. Nagahara, S. Kuthirummal, C. Zhou, and S. Nayar

The depth of field (DoF) of a lens is confined to a frontal-parallel slab. In this paper, the authors attempt to break this limitation by proposing flexible depth of field photography, i.e. to translate the detectors within the shutter. Thus at each moment the lens produces a point spread function (PSF) associated with the sensor position, and the final PSF, called integrated PSF (IPSF) is the sum of all the PSFs produced over the exposure.

Under this scheme, the authors suggested three applications for manipulating DoF. In the first application, the sensors are translated uniformly to produce a depth-independent, frequency preserving IPSF, ensuring a good quality of the restored all-in-focus image. In the second application, the authors play with non-uniform translations. Unwanted depth layers in the middle can be skipped so that their image would be blurry enough to be unnoticeable. The authors also showed that by rolling the detector’s exposure time during the translation, an arbitrary shape of DoF can be produced. All the applications are realized with a prototype flexible DoF imaging system built by the author.

The idea of flexible DoF is interesting, but it is not as novel as the authors claim in the paper. Although never thoroughly investigated, focus sweep is a widely used technique in photography under the name variable-focus photography; uniform sweeping of the DoF was even proposed as early as 1972 by Hausler. The major difference between Hausler’s work and this paper is just replacing focus sweeping with sensor translation, which is minor. The usefulness of the other two applications are somewhat vague due to the underlying assumption that scene depth is known before capture.