  This paper describes a novel approach to partially reconstruct
high-resolution 4D light fields from a stack of differently focused photographs
taken with a fixed camera. First, a focus map is calculated from this stack
using a simple approach combining gradient detection and region expansion with
graph-cut. Then, this focus map is converted into a depth map thanks to the
calibration of the camera. We proceed after this with the tomographic
reconstruction of the epipolar images by back-projecting the focused regions of
the scene only. We call it masked back-projection. The angles of
back-projection are calculated from the depth map. Thanks to the high angular
resolution we achieve by suitably exploiting the image content captured over a
large interval of focus distances, we are able to render puzzling perspective
shifts although the original photographs were taken from a single fixed camera
at a fixed position.
