Ventseslav Sainov

3-D Time-Varying Scene Capture Technologies—A Survey

Advances in image sensors and evolution of digital computation is a strong stimulus for development and implementation of sophisticated methods for capturing, processing and analysis of 3D data from dynamic scenes. Research on perspective time-varying 3D scene capture technologies is important for the upcoming 3DTV displays. Methods such as shape-from-texture, shape-from-shading, shape-from-focus, and shape-from-motion extraction can restore 3D shape information from a single camera data. The existing techniques for 3D extraction from single-camera video sequences are especially useful for conversion of the already available vast mono-view content to the 3DTV systems. Scene-oriented single-camera methods such as human face reconstruction and facial motion analysis, body modeling and body motion tracking, and motion recognition solve efficiently a variety of tasks. 3D multicamera dynamic acquisition and reconstruction, their hardware specifics including calibration and synchronization and software demands form another area of intensive research. Different classes of multiview stereo algorithms such as those based on cost function computing and optimization, fusing of multiple views, and feature-point reconstruction are possible candidates for dynamic 3D reconstruction. High-resolution digital holography and pattern projection techniques such as coded light or fringe projection for real-time extraction of 3D object positions and color information could manifest themselves as an alternative to traditional camera-based methods. Apart from all of these approaches, there also are some active imaging devices capable of 3D extraction such as the 3D time-of-flight camera, which provides 3D image data of its environment by means of a modulated infrared light source.

Fringe projection with a sinusoidal phase grating

Phase-shifting profilometry requires projection of sinusoidal fringes on a 3D object. We analyze the visibility and frequency content of fringes created by a sinusoidal phase grating at coherent illumination. We derive an expression for the intensity of fringes in the Fresnel zone and measure their visibility and frequency content for a grating that has been interferometrically recorded on a holographic plate. Both evaluation of the systematic errors due to the presence of higher harmonics by simulation of a profilometric measurement and measurement of 3D coordinates of test objects confirm the good performance of the sinusoidal phase grating as a projective element. In addition, we prove theoretically that in comparison with a sinusoidal amplitude grating this grating produces better quality of fringes in the near-infrared region. Sinusoidal phase gratings are fabricated easily, and their implementation in fringe projection profilometry facilitates construction of portable, small size, and low-cost devices.

New automatic FFT filtration method for phase maps and its application in speckle interferometry

In this article a new automatic phase FFT filtration method is described. It is compared with other well known filtration techniques for noise removal. This automatic FFT filter is applied on interferograms obtained through one dimensional folding shear interferometry for displacements measurement of a loaded glass flask. Different algorithms have been applied for processing of digitally synthesized phase maps and the advantages of the enhanced automatic FFT filtration are shown. The phase filtered maps obtained in this way can be demodulated even with the simplest unwrapping technique.

Compact electronic speckle pattern interferometer using a near infrared diode laser and a reflection holographic optical element

The complicated experimental set-ups required for existing electronic speckle pattern interferometers limit their application potential. To overcome the limitations we present a simple and very compact electronic speckle pattern interferometer. Our system does not use expensive and complicated optical elements. We used a near infrared reflection holographic optical element for the first time in an out-of-plane sensitive electronic speckle pattern interferometer operating with a near infrared diode laser. The use of a holographic optical element drastically reduces the number of optical elements; the final system only consists of a CCD camera, a HOE and a test object, with significant reductions in system costs and time spent aligning the system. Reflection holographic optical elements were recorded in HP-650 emulsions using a He?Ne laser. The hologram was reconstructed using a laser diode operating at 784?nm by swelling the emulsion. Current modulation of the laser diode was utilized to introduce the desired phase shifts for fringe analysis.

Noise filtering in the interference pattern by dynamic holographic recording in photorefractive Bi(12)TiO(20) crystals.

The possibilities of stabilization of the interference pattern by filtration of a random-phase noise caused by vibrations, turbulence, and other local changes in the wave front in interferometric measurements are investigated. Dynamic holographic recording in photorefractive Bi(12)TiO(20) crystals is used. The parameters of the holographic recording are presented for determination of the dynamic range for filtering. Noise filtering takes place in real time and contributes to the enhancement of the contrast and the signal-to-noise ratio of the interference pattern. This results in a considerable increase in the sensitivity and the accuracy of the interferometric measurements.

The growth and optical properties of doped bismuth titanate

Abstract The growth conditions for producing Al, Mn, Cr and Al+Cr doped Bi 12 TiO 20 crystals have been studied. Transmission spectra of various crystals have been measured and the absorption has been determined in the range 0.4 – 0.85 μm. A blue shift in the spectral absorption of Al doped Bi 12 TiO 20 and a red shift in Mn, Cr and Al+Cr doped Bi 12 TiO 20 has been observed as compared to undoped material. In Al+Cr doped crystals the absorption is blue-shifted as compared to Cr-only doping.

Monitoring of bread cooling by statistical analysis of laser speckle patterns

The phenomenon of laser speckle can be used for detection and visualization of physical or biological activity in various objects (e.g. fruits, seeds, coatings) through statistical description of speckle dynamics. The paper presents the results of non-destructive monitoring of bread cooling by co-occurrence matrix and temporal structure function analysis of speckle patterns which have been recorded continuously within a few days. In total, 72960 and 39680 images were recorded and processed for two similar bread samples respectively. The experiments proved the expected steep decrease of activity related to the processes in the bread samples during the first several hours and revealed its oscillating character within the next few days. Characterization of activity over the bread sample surface was also obtained.

Pattern projection with a sinusoidal phase grating

The aim of this work is to study the diffractive properties of a sinusoidal phase grating for incorporation as a pattern projection element in a multisource and multicamera phase-shifting profilometric system. Two challenges should be overcome for successful operation of such a system, which are connected to inherent limitations of the phase-shifting algorithm—requirements for a sinusoidal fringe profile and for equal background and contrast of fringes in the recorded patterns. As a first task, we analyze the frequency content of the projected fringes in the Fresnel diffraction zone for parallel and divergent light illumination at different grating parameters and wavelengths. As a second task, we evaluate the systematical errors due to higher harmonics and multiwavelength illumination. Finally, operation of the four-wavelength profilometric system is simulated, and the error of the profilometric measurement evaluated. The results of test measurements are also presented.

Real time phase stepping pattern projection profilometry

A single-shot fringe projection profilometry system based on simultaneous projection of four phase-shifted sinusoidal fringe patterns generated at four different wavelengths is described. The system includes a fringe pattern generation module containing four blocks with four near-infrared diode lasers and a registration module with four CCD cameras. In order to simplify the technical solution and to avoid the stringent requirement for stability in the case of interferometric fringe generation, we study both theoretically and experimentally realization of the proposed system by using of a phase grating as well as a holographic optical element for reconstruction of two point sources. The results of the measurement of the relative and absolute coordinates of test objects for both types of diffraction gratings are presented.

Interferometer based on total internal reflection.

An interferometer is investigated in which the interacting beams undergo total internal reflection from a boundary surface with a variable relative refractive index. The high sensitivity of the change in the interference pattern with respect to small changes in the refractive index in the vicinity of the critical angle is theoretically proved and experimentally confirmed.