Baozhen Ge

Digital holography and its application

The theory and the method of digital holography and its application have been studied, and part of the study results mainly involving eliminating zero-order diffraction in digital off-axis holography, analysis of the influence factors of the reconstructed image quality, particle field measurement, etc. are reported, and the experimental results are also given. The preliminary investigative basic research in color digital holography has been done. Multiple-wavelength recording system is introduced in digital holography, and recording of hologram by CCD is no longer a single wavelength one, which is a beneficial tentative research for the development of color digital holography. The research and the results provide the initial theory and experimental basis for the further advancement of digital holography.

Color 3D digital human modeling and its applications to animation and anthropometry

With the rapid advancement in laser technology, computer vision, and embedded computing, the application of laser scanning to the digitization of three dimensional physical realities has become increasingly widespread. In this paper, we focus on research results embodied in a 3D human body color digitization system developed at Tianjin University, and in collaboration with the Hong Kong University of Science and Technology. In digital human modeling, the first step involves the acquisition of the 3D human body data. We have over the years developed laser scanning technological know-how from first principles to support our research activities on building the first 3D digital human database for ethnic Chinese. The disadvantage of the conventional laser scanning is that surface color information is not contained in the point cloud data. By adding color imaging sensors to the developed multi-axis laser scanner, both the 3D human body coordinate data and the body surface color mapping are acquired. Our latest development is focused on skeleton extraction which is the key step towards human body animation, and applications to dynamic anthropometry. For dynamic anthropometric measurements, we first use an animation algorithm to adjust the 3D digital human to the required standard posture for measurement, and then fix the feature points and feature planes based on human body geometric characteristics. Utilizing the feature points, feature planes, and the extracted human body skeleton, we have measured 40 key sizes for the stand posture, and the squat posture. These experimental results will be given, and the factors that affect the measurement precision are analyzed through qualitative and quantitative analyses.

Auto-calibration of a Laser 3D Color Digitization System

A typical 3D color digitization system is composed of 3D sensors to obtain 3D information, and color sensors to obtain color information. Sensor calibration plays a key role in determining the correctness and accuracy of the 3D color digitization data. In order to carry out the calibration quickly and accurately, this paper introduces an automated calibration process which utilizes 3D dynamic precision fiducials, with which calibration dot pairs are extracted automatically, and as the corresponding data are processed via a calibration algorithm. This automated was experimentally verified to be fast and effective. Both the 3D information and color information are extracted such that the 3D sensors and the color sensors are calibrated with one automated calibration process. We believe it is the first such calibration process for a 3D color digitization system.

Design of the experimental system of digital off-axis holography and analysis of zero-order image

The simple hologram recording system of digital off-axis holography is designed. Holographic diffraction grating of low spatial frequency is introduced to digital holography, acting as a beam splitter, illuminated by the monochrome plane parallel light wave, and the three different plane parallel light waves, namely, the zero-order and the ±1order diffraction waves, are generated. An off-axis holography system is configurated between the +1/-1order diffraction waves and the zero-order wave. The theoretical analysis has been done in detail and the zero-order diffraction in the reconstructed image of digital off-axis holography is also analyzed theoretically. The experimental results are given. The feasibility of the experimental system presented in this paper was confirmed, simple in optical structure and easy in operation. In addition, the zero-order image can be eliminated by numerically processing the holograms of object with different recording parameters obtained by adjusting the reflecting mirror in the recording optical system to vary the incidence beam orientation in CCD to introduce a phase shift.

Microstructure testing with digital holography

An optical system of digital holography based on 4f system for microstructure measurement is studied. Fresnel off-axis hologram generated by a magnified image of microstructure is recorded with a CCD, and the magnified reconstructed image can be obtained by the angular spectrum method. The quantitative phase information of the microstructure under test is obtained. A theoretical analysis is performed in detail and the experiment done, and the experimental results are also given. The research shows that the method presented in this paper can be applied to micro-object imaging and its quantitative measurement.

Study on broadening the size range in laser particle size measurement by combined spectrum technology

In laser particle size measurement, the instrument based on traditional Fourier transform structure is disadvantaged in the narrow measurable dynamic size range. So it is hardly to be used to measure broadly distributed particle. The presented technology is based on Fresnel diffraction theory. The formula of combined spectrum technology by detecting signals on coaxial focal planes is educed. In the proposed method, the two lenses are set coaxially and signals are detected on the back focal plane of the first lens and the combined back focal plane of the two lenses. The detected signals are then combined. The data are processed with a no-model algorithm. Thus, the measurable dynamic range can be broadened as no component of the sizer is changed. Experimental results of some samples show that the particulate in the size range of 5 ~ 3500 µm can be measured simultaneously.

Size measurement of standing and sitting position based on human animation

A method of measuring the key sizes of a human 3D mesh model was presented. In the proposed method, human model postures were adjusted according to the measuring reference plane, measuring direction and measuring points. Then the skeleton of the model was extracted through the gradient rapid descent algorithm of the radial base function. What follows was to locate the joints and set their freedom and active ranges. Then, the surface peaks were bonded to the joints through flexible models to implement human animation. In this way, the standing and sitting poses were obtained. After automatic means of body characteristic points location had been studied, the points and plane were extracted to locate the measuring points precisely. Experiments were carried out on a man respectively and their key sizes were shown.

Low-density microporous polymeric foams measurement with digital microscopic image plane holography

A method for the measurement of low-density microporous polymeric foams with digital microscopic image plane holography is studied. An image plane hologram of microporous foam is recorded in an optical system of a Mach-Zender interferometer by CCD sensor, and the magnified image, which contains the quantitative information of the intensity and the phase of the microporous foam, is reconstructed numerically from the captured single interference pattern by twice fast Fourier transform and digital filter processing of frequency spectrum. And the morphometry and the pore diameter of the microporous foam under test can be obtained. A theoretical analysis has been performed and experimental results of the polymeric foam are also given. The experimental results show that the method presented in this paper is feasible, easy in data processing.

Method for searching the mapping relationship between space points and their image points in CCD camera

BP Neural Network Method and Linear Partition Method are proposed to search the mapping relationship between space points and their image points in CCD cameras, which can be adopted to calibrate three-dimensional digitization systems based on optical method. Both of the methods only need the coordinates of calibration points and their corresponding image points’ coordinates as parameters. The principle of the calibration techniques includes the formula and solution procedure is deduced in detail. Calibration experiment results indicate that the use of Linear Partition Method to coplanar points enables its measuring mean relative error to reach 0.44 percent and the use of BP Neural Network Method to non-coplanar points enables its testing accuracy to reach 0.5-0.6 pixels.