Bhupendra Bimal Chhetri

Iterative stepwise binarization of digital amplitude holograms with added energy to the signal window

We propose a method for optimizing the process of iteratively binarizing digital amplitude holograms by utilizing the effect of adding energy to the reconstructed signal window from the hologram. For this purpose, we introduce a parameter called the energy factor and show that the performance of the iterative binarization process can be greatly enhanced if the value of the energy factor is properly chosen. Finally, we show that the optimal values of this energy factor can be estimated with an analytical function for different computational costs.

Stochastic approach in the efficient design of the direct-binary-search algorithm for hologram synthesis.

An algorithm incorporating a stochastic approach is proposed for reducing the computation time of the direct-binary-search algorithm for hologram synthesis. Two variants of this new algorithm are considered for a number of hologram-generation problems. Both variants can reduce the computation time significantly with a very small increase in the reconstruction error on average. The effectiveness of the proposed algorithm is found to improve with the increasing computational complexity of the design problem. Also, the algorithm is able to generate the hologram in a time that is relatively independent of the initial conditions.

Binary phase difference diffuser: Design and application in digital holography

Design of a simple diffuser, in which the absolute value of the phase difference between the diffusers adjacent samples is constant, is considered. A condition is imposed in the design so that the diffuser is suitable for use with the iterative method based on the iterative Fourier transform algorithm for calculating a two-dimensional complex amplitude function that possesses a bandlimited and smooth spectrum. A method for effectively designing this diffuser is proposed, and its application in the field of digital holography is presented.

Heuristic algorithm for calculation of sufficiently randomized object-independent diffuser for holography

In this paper, we consider a simple object-independent diffuser for digital holography that is characterized by a constant absolute value of the phase difference between its samples. In order to have desirable characteristics, the distribution of the signs of phase difference of it must be sufficiently randomized. We thus propose an effective algorithm for this purpose. Finally, we show that this diffuser can be used to initialize the phase of an intensity object for successfully calculating its complex amplitude, which is band-limited and at the same time possesses a smooth spectrum, and which fulfills the basic requirement for efficiently encoding it into a hologram and reconstructing it with reduced speckles.

Design of binary Fourier holograms using DBS for reduced-speckle-reconstruction

The design of binary amplitude holograms using direct-binary-search (DBS) method for reduced-speckle-reconstruction is considered. Two design approaches are considered and their dependencies on the initial conditions are investigated.

Iterative calculation of the quasi-bandlimited diffuser in two dimensions from restricted phase distributions

We present a performance comparison of various initial phase distributions that provide successful iterative calculation of two-dimensional quasi-bandlimited diffusers for holographic use. Phase filtering concept is introduced to make previously unsuitable phase distribution suitable. Phase distributions obtained from the superposition of the one dimensional quasi-bandlimited diffuser, binary phase difference diffuser, and filtered restricted phase psuedorandom diffuser introduced in this article are considered.

Speckle reduction of kinoform reconstruction by utilizing the 2π ambiguity of image phase differences

The speckle noise is a serious problem in the reconstructed images from kinoforms. A random phase added to the desired image can reduce the dynamic range of its Fourier spectrum, but this involves the speckle noise. In general, isolated first-order zeros in band-limited complex amplitudes are always surrounded by phase change from -π to π. These isolated zeros may cause the speckle noise in kinoform reconstruction. The isolated zeros are lead from a 2π circle of the reconstructed image phase differences. We suggest a new iterative algorithm to optimize the desired image phases in order to reduce the isolated zeros. Experimental results showed that our new iterative algorithm is effective for the speckle reduction of kinoform reconstruction.

Error reduction of amplitude digital Fourier transform holograms by use of a preiterative process

It is well known that the iterative stepwise quantization algorithm is very powerful for the optimization of amplitude digital Fourier transform holograms. We suggest a pre- iterative process to uniform the histogram distribution of the Fourier transform of the input image in order to reduce the reconstruction error of amplitude digital Fourier transform holograms. Simulation results show that the reconstruction error can be reduced much when our pre- iterative process is used in the iterative stepwise quantization algorithm.