• 한국가시화정보학회:학술대회논문집
• /
• 2005.12a
• /
• pp.1-5
• /
• 2005

The digital HPTV velocity field measurement consists of four steps: recording, numerical reconstruction, particle extraction and velocity extraction. In the velocity extraction process, we improved PTV algorithm to extract the displacement of particle each placed in 3D space. Because a digital recording device was used, some factors such as a spatial resolution, numerical aperture, and particle concentration can affect the performance of the digital HPTV. Especially, a particle concentration ($C_{o}$) affected tile reconstruction efficiency in numerical reconstruction and particle extraction process. In this paper, the reconstruction efficiency was analyzed experimentally with different particle concentration. Optimal reconstruction efficiency was shown in the range of $C_{o}$=$13\∼15$ particles/$mm^{3}$.

• Journal of ILASS-Korea
• /
• v.15 no.2
• /
• pp.53-60
• /
• 2010

This study presents development of digital particle holographic system and its application to spray field to measure three-dimensional velocities and sizes of spray droplets. A double exposure hologram recording system with synchronization system for time control was established and digital holograms can be recorded in a short time interval. To process recorded holograms, the correlation coefficient method was used for focal plane determination of particles. To remove noises and improve the quality of holograms and reconstructed images, the Wiener filter was adopted. The two-threshold and image segmentation methods were used in binary image transformation. For particle pairing, the match probability method was adopted. The developed system was applied to spray field and three-dimensional velocities and sizes of spray droplets were measured. The measurement results of digital holographic system were compared with those made by laser instruments, PDPA(Phase Doppler Particle Analyzer), which proved the feasibility of in-line digital particle holographic system as a good measurement tool for spray droplets.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.30 no.10 s.253
• /
• pp.929-934
• /
• 2006

The digital HPTV(holographic particle tracking velocimetry) velocity field measurement system consists of four steps: recording, numerical reconstruction, particle extraction and velocity extraction. In the velocity extraction process, we improved the two frame PTV algorithm to extract 3-D displacement information of each particle located in 3D space. Because a digital CCD camera was used, some factors such as spatial resolution, numerical aperture, and particle concentration influenced on the performance of the developed digital HPTV. Especially, the particle concentration $(C_o)$ affected the reconstruction efficiency and recovery ratio in the numerical reconstruction and particle extraction procedure. In this paper, the effect of particle concentration reconstruction efficiency and recovery ratio were analyzed experimentally. Optimal particle concentration was found to be in the range of $C_o=11{\sim}17\;particles/mm^3$.

• Imaging Science in Dentistry
• /
• v.43 no.3
• /
• pp.185-190
• /
• 2013

Purpose: The aim of the present study was to evaluate the measurement accuracy of endodontic file length on periapical digital radiography after application of noise reduction digital enhancement. Materials and Methods: Thirty-five human single-rooted permanent teeth with canals measuring 20-24 mm in length were selected. ISO #08 endodontic files were placed in the root canals of the teeth. The file lengths were measured with a digital caliper as the standard value. Standard periapical digital images were obtained using the Digora digital radiographic system and a dental X-ray unit. In order to produce the enhanced images, the noise reduction option was applied. Two blinded radiologists measured the file lengths on the original and enhanced images. The measurements were compared by repeated measures ANOVA and the Bonferroni test (${\alpha}=0.05$). Results: Both the original and enhanced digital images provided significantly longer measurements compared with the standard value (P<0.05). There were no significant differences between the measurement accuracy of the original and enhanced images (P>0.05). Conclusion: Noise reduction digital enhancement did not influence the measurement accuracy of the length of the thin endodontic files on the digital periapical radiographs despite the fact that noise reduction could result in the elimination of fine details of the images.

• International Journal of Concrete Structures and Materials
• /
• v.10 no.2
• /
• pp.189-203
• /
• 2016

This paper investigates on the use of advanced optical measurement methods, i.e. 3D coordinate measurement machines (3D CMM) and stereo-vision digital image correlation (3D DIC), for the mechanical analysis of shear deficient prestressed concrete members. Firstly, the experimental program is elaborated. Secondly, the working principle, experimental setup and corresponding accuracy and precision of the considered optical measurement techniques are reported. A novel way to apply synthesised strain sensor patterns for DIC is introduced. Thirdly, the experimental results are reported and an analysis is made of the structural behaviour based on the gathered experimental data. Both techniques yielded useful and complete data in comparison to traditional mechanical measurement techniques and allowed for the assessment of the mechanical behaviour of the reported test specimens. The identified structural behaviour presented in this paper can be used to optimize design procedure for shear-critical structural concrete members.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2004.05a
• /
• pp.495-498
• /
• 2004

In the sound insulation measurements, the influence of background (extraneous) noise is often serious problem and how to reduce its effect and to improve the signal-to-noise(S/N) ratio is an important theme. As the background noise, such extraneous noises as road traffic noise and machine noise often disturb the measurement. In laboratory measurements on specimens with high sound insulation performances, even the internal noise of the measurement system can become a problem. To improve the signal-to-noise ratio and to improve the measurement accuracy, various kinds of digital signal processing techniques can be applied. In this paper, four kinds of digital signal processing techniques are applied and their effectiveness is examined by a simple sound insulation measurement.

• Korean Journal of Optics and Photonics
• /
• v.31 no.3
• /
• pp.134-141
• /
• 2020

Optical three-dimensional (3D) measurement systems based on digital fringe projection are used in many contactless measurement applications. The system which can measure a dozen micrometers uses a liquid-crystal display (LCD) as the projection unit for generating a digital fringe pattern, because a flexible fringe pattern can be easily made by computer software. According to the gamma nonlinearity of the LCD projection unit, the digital fringe projection error on the object affects the accuracy of 3D object measurement. An improved method of LCD gamma-nonlinearity error reduction is proposed, by using the inverse function of the intensity transfer function to improve the accuracy. The improvement due to the proposed method is shown by measuring the difference in precision between a computer-generated sine wave and a camera-obtained sine wave for a standard semiconductor specimen.

• Journal of Advanced Navigation Technology
• /
• v.23 no.4
• /
• pp.316-321
• /
• 2019

In this paper, by applying the constant current principle we develop an impedance measurement system which can measure the high precision impedance of various electric materials by using microprocessor. This measurement system board has an interface device for acquiring digital data from an external device including an impedance measuring device, and system software is also developed by a firmware program executed on such an embedded board. It can measure the high precision impedance of a specific band with 1/32768 precision by using 15-bit ADC(analog to digital converter) and calculate it to the five digits to the right of the decimal point(fraction part). Data is transmitted through a USB interface of a general computer and a measuring device to manage digital data. An impedance measurement system equipped with a communication function capable of a more general and easy-to-use interface than other equipment is developed and verified.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2007.09a
• /
• pp.465-477
• /
• 2007

Recently a number of research has been performed for the combination of new high technologies in order to find the solutions for various problems in civil engineering research field. Various high-tech measuring instruments have been applied to the geotechnical engineering field, and many attempts have also been performed for the more accurate measurements. Especially, the researches using image on the digital photogrammetry technique are gradually extending nowadays. The computer program developed using the digital photogrammetry technique and the case studies are explained and presented in this paper. Therefore, it could be considered that not only the measurement with high-accuracy but the disaster prevention should be available through the practical use of digital photogrammetry technique. The applicability would also be increased in the measurement of both the geotechnical engineering field as well as other research fields.

• Journal of the Optical Society of Korea
• /
• v.13 no.2
• /
• pp.245-250
• /
• 2009

We propose a digital holographic interference analysis method based on a 2-frame phase-shifting technique for measuring an optical mirror surface. The technique using 2-frame phase-shifting digital interferometry is more efficient than multi-frame phase-shifting techniques because the 2-frame method has the advantage of a reduced number of interferograms, and then takes less time to acquire the wanted topography information from interferograms. In this measurement system, 2-frame phase-shifting digital interferograms are acquired by moving the reference flat mirror surface, which is attached to a piezoelectric transducer, with phase step of 0 or $\pi$/2 in the reference beam path. The measurements are recorded on a CCD detector. The optical interferometry is designed on the basis of polarization characteristics of a polarizing beam splitter. Therefore the noise from outside turbulence can be decreased. The proposed 2-frame algorithm uses the relative phase difference of the neighbor pixels. The experiment has been carried out on an optical mirror which flatness is less than $\lambda$/4. The measurement of the optical mirror surface topography using 2-frame phase-shifting interferometry shows that the peak-to-peak value is calculated to be about $0.1779{\mu}m$, the root-mean-square value is about $0.034{\mu}m$. Thus, the proposed method is expected to be used in nondestructive testing of optical components.