A fast and memory-efficient Discrete Focal Stack Transform for plenoptic sensors

Plenoptic cameras are a new type of sensors that capture the four-dimensional lightfield of a scene. Processing the recorded lightfield, they extend the capabilities of current commercial cameras. Conventional cameras obtain photographs focusing at a determined depth. This photograph can be described through a projection of the four-dimensional lightfield onto two spatial dimensions. The collection of such images is the focal stack of the scene. The focal stack can be used to select an image refocused at a certain depth, to recover 3D information or to obtain all-in-focus images. There are several approaches to the computation of the focal stack. In this paper we propose a new technique to compute the focal stack by means of its frequency decomposition that can be seen as an extension of the Discrete Focal Stack Transform (DFST). This new approach decreases the computational complexity of the DFST maintaining an efficient memory use. Experimental results are provided to show the validity of the technique and its extension to 3D processing and all-in-focus image computation is also studied.