Fast Extended Depth-of-Field Reconstruction for Complex Holograms Using Block Partitioned Entropy Minimization

• Published in: Applied sciences 2018-05, Vol.8 (5), p.830
• Main Authors: Tsang, Peter, Poon, Ting-Chung, Liu, Jung-Ping
• Format: Article
• Language: English
• Subjects: automatic focus detection; Axes (reference lines); Birefringence; block partitioned entropy minimization; Depth of field; Digital photography; Entropy; entropy minimization; extended depth-of-field; Haze; Holograms; Holography; Image processing; Laser beams; Linear polarization; Microscopy; optical scanning holography; Optimization; Pixels; Plane waves; Remote sensing; Spherical waves; Wave plates; Zone plates
• ISSN: 2076-3417; 2076-3417
• DOI: 10.3390/app8050830

[...]a focused image of the object points that are contained in each of the focused section is obtained through an iterative optimization process, while the de-focused haze will be discarded. A linearly polarized laser of wavelength λ is passed through a half-wave plate (HWP), which rotates the polarization direction of the laser beam along the bisector of the two principal axes of the electro-optic crystal of the electro-optic modulator (EOM). Since there is birefringence induced along one of the principal axes through external electrical saw-tooth signal, the output beam of the EOM contains two orthogonal polarizations with a frequency difference Ω. [...]on the sample, we have a time-dependent Fresenl zone plate (TD-FZP) as the interference of a plane wave and a spherical wave gives an FZP and the frequency difference Ω of the two beams gives running fringes within the overall scanning beam on the sample [1,2]. [...]in stage 4, an extended depth of field image of the object scene is obtained by selecting each pixel from the reconstruction image plane that corresponding to the depth of the pixel in the depth map.