Fast approximate focal stack transform

In this work we develop a new algorithm, extending the fast digital Radon transform from Gotz and Druckmuller (1996), that is capable of generating the approximate focal stack of a scene, previously measured with a plenoptic camera, with the minimum number of operations. This new algorithm does not require multiplications, just sums, and its computational complexity is O(N⁴) to achieve a volume consisting of 2N - 1 photographic planes focused at different depths, from a N⁴ light field. The method is close to real-time performance, and its output can be used to estimate the distances to objects of a scene.