  Light field deconvolution allows three-dimensional investigations from a
single snapshot recording of a plenoptic camera. It is based on a linear image
formation model, and iterative volume reconstruction requires to define the
backprojection of individual image pixels into object space. This is
effectively a reversal of the point spread function (PSF), and backprojection
arrays H' can be derived from the shift-variant PSFs H of the optical system,
which is a very time consuming step for high resolution cameras. This paper
illustrates the common structure of backprojection arrays and the significance
of their efficient computation. A new algorithm is presented to determine H'
from H, which is based on the distinct relation of the elements' positions
within the two multi-dimensional arrays. It permits a pure array
re-arrangement, and while results are identical to those from published codes,
computation times are drastically reduced. This is shown by benchmarking the
new method using various sample PSF arrays against existing algorithms. The
paper is complemented by practical hints for the experimental acquisition of
light field PSFs in a photographic setup.
