Focus on a single plane is a linear process that can be carried out by a conventional lens. Focus on a volume is also a linear process, but to our knowledge there is no optical system that can perform volumetric focus. Planar focus creates a single plane of sharp focus within a scene, and ”blurs” elements as you move away from that plane — the larger the aperture, the sharper the falloff. Volumetric focus puts a ”range” of depths in focus, and blurs elements as you move away from the focal volume. The rate at which the blur increases is a tunable filter parameter, with an upper bound determined by the light field camera’s aperture.
All of the above example are single-step linear filters, implemented as a spatial convolution between the 4D input light field and a real-valued 4D impulse response. The output in each case is a 4D light field — shown here are 2D slices.
Here are some examples demonstrating a hyperfan filter cutting through murky water. In the below, the filter is implemented directly in the frequency domain.
Please refer to our SPIE 2013 paper for further information:
D. G. Dansereau, D. L. Bongiorno, O. Pizarro, and S. B. Williams, “Light field image denoising using a linear 4D frequency-hyperfan all-in-focus filter,” in Proceedings SPIE Computational Imaging XI, Feb 2013. Available here.