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Quantization is widely used for compression, storage, transmission and display of computer-generated and digital holograms. It reduces number of hologram gradations to obtain better ratio of the quality of reconstructed 2D and 3D objects to the size of holographic images or videos. This paper proposes 2 methods of non-iterative quantization of holograms: adaptive non-uniform quantization based on histogram processing with peak shift (ANHS method) and additional application of logarithmic companding (ANHSL method). They were compared with 4 methods of iterative and non-iterative quantization on holograms with sizes up to 2048 × 2048 pixels. The proposed methods showed the best reconstruction quality that is higher up to 59 % in comparison with non-iterative uniform quantization. Especially the proposed methods give higher quality at little number of hologram gradations (from 2 to 16 gradations). In comparison with the most qualitative iterative methods (Lloyd-Max and k-means) the quality is increased up to 9 %, and processing time is reduced in 10–1000 times. [ABSTRACT FROM AUTHOR]

Optical scanning holography (OSH) is a distinct digital holography technique, which uses a single two-dimensional (2D) scanning process to record the hologram of a three-dimensional (3D) object. Usually, these 2D scanning processes are in the form of mechanical scanning, and the quality of recorded hologram may be affected due to the limitation of mechanical scanning accuracy and unavoidable vibration of stepper motor’s start-stop. In this paper, we propose a new framework, which replaces the 2D mechanical scanning mirrors with a Digital Micro-mirror Device (DMD) to modulate the scanning light field, and we call it OSH based on Compressive Sensing (CS) using a digital micro-mirror device (CS-OSH). CS-OSH can reconstruct the hologram of an object through the use of compressive sensing theory, and then restore the image of object itself. Numerical simulation results confirm this new type OSH can get a reconstructed image with favorable visual quality even under the condition of a low sample rate. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we propose a novel method to detect the best reconstructing distance in phase-shifting digital holography, which can help one to reconstruct high-quality images even though the recording distance is unkonwn. This scheme is based on an algorithm, two-dimensional discrete cosine transform (DCT). Numerical experiments for this method are shown in this paper. It is shown that this method is not only effective but also fast compared to previous schemes for detecting the focal distance in digital holography. Meanwhile, the algorithm can be effective against different types of noise. [Copyright &y& Elsevier]

Abstract: Digitally-recorded holograms are numerically reconstructed to reveal the 3D profile of the object. When the distance of the object to the recording plane is not known a priori, one has to perform reconstruction at discrete steps and decide the best focus distance according to some criteria. There are autofocusing algorithms that utilize a metric to assess the quality of the images, such as the sharpness of the object, to decide the best focus distance. However, the computational cost of this search rapidly increases as the resolution of the system becomes higher since the object image has to be numerically reconstructed from the hologram first. Here, we investigate the behavior of the sharpness curves of the object images obtained from the scaled holograms. We find that it is possible to estimate the autofocus distance accurately with this scaling, and the resultant autofocus speed improvement is on the order of square of the scaling ratio. Experimental results are presented and they are in excellent agreement with the simulations. [Copyright &y& Elsevier]

A modification of the classical calculation algorithm is presented which allows to minimize the effect of the long range oscillations created by the twin object in the reconstruction process of in-line holograms obtained by low energy electron projection microscopy. The reconstructed shapes of a tungsten tip, observed with different magnifications are shown. [Copyright &y& Elsevier]