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Daolei Wang

Bio: Daolei Wang is an academic researcher from National University of Singapore. The author has contributed to research in topics: Epipolar geometry & Depth map. The author has an hindex of 6, co-authored 7 publications receiving 136 citations.

Papers
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Journal ArticleDOI
TL;DR: The algorithm of segment-based stereo matching using graph cuts is developed for extracting depth information from the stereo image pairs by employing the mean-shift algorithm and the use of Adaptive Support Weighted Self-Adaptation dissimilarity algorithm for the estimation of initial disparity.

42 citations

Journal ArticleDOI
TL;DR: A transformation matrix is derived which can express the relationship between an object point and its image by the refraction of a prism and is used for epipolar geometry and three-dimensional point reconstruction.
Abstract: In this paper, we proposed a new method for analyzing the image formation of a prism. The prism was considered as a single optical system composed of some planes. By analyzing each plane individually and then combining them together, we derived a transformation matrix which can express the relationship between an object point and its image by the refraction of a prism. We also explained how to use this matrix for epipolar geometry and three-dimensional point reconstruction. Our method is based on optical geometry and could be used in a multiocular prism. Experimentation results are presented to prove the accuracy of our method is better than former researchers’ and is comparable with that of the multicamera stereovision system.

35 citations

Journal ArticleDOI
TL;DR: A simple geometrical ray approach to calibrate the extrinsic parameters of the virtual cameras and solve the stereo correspondence problem of the single-lens bi-prism stereovision system is proposed.
Abstract: This paper proposes a simple geometrical ray approach to calibrate the extrinsic parameters of the virtual cameras and solve the stereo correspondence problem of the single-lens bi-prism stereovision system. Each images captured using this system can be divided into two sub-images which are generated by two virtual cameras due to the refraction through the bi-prism. This stereovision system is equivalent to the conventional two camera system and the two captured sub-images provide disparity which can be used for depth recovery. The virtual cameras will be calibrated geometrically and the correspondence problem of this system will be solved by applying epipolar geometry constraint on the generated virtual cameras instead of the real CCD camera. Experiments are conducted to validate the proposed method and the results are compared to the conventional approach to confirm its accuracy and effectiveness.

22 citations

Journal ArticleDOI
01 May 2013
TL;DR: A geometry-based method is proposed to determine the pose of virtual cameras and obtain the rotational and translational transformation matrix to real camera and the rectification transformation matrix which applied on the images captured using the system is computed.
Abstract: This paper proposes a new method for rectification of single-lens stereovision system with a triprism. The image plane of this camera will capture three different views of the same scene behind the filter in one shot. These three sub-images can be taken as the images captured by three virtual cameras which are generated by the three Face (3F) filter (triprism). A geometry-based method is proposed to determine the pose of virtual cameras and obtain the rotational and translational transformation matrix to real camera. At the same time, the parallelogram rule and refraction rule are employed to determine the desired sketch ray functions. Followed by this, the rectification transformation matrix which applied on the images captured using the system is computed. The approach based on geometry analysis of ray sketching is significantly a simpler implementation: it does not require the usual complicated calibration process. Experimental results are presented to show the effectiveness of the approach.

19 citations

Journal ArticleDOI
TL;DR: A geometrical approach for virtual camera rectification on uncalibrated single-lens stereovision using a biprism that provides a simple stereo matching technique for this system.
Abstract: We propose a geometrical approach for virtual camera rectification on uncalibrated single-lens stereovision using a biprism. This system is also called a virtual stereovision system, as the image captured can be divided into two which are equivalent to two images captured using two cameras with different perspectives. The proposed method is divided into two parts. The first part is to compute the projection transformation matrix of two virtual cameras based on a unique geometrical ray sketching, which can accurately recover the extrinsic parameters, and the second part is to compute the rectification transformation matrix, which is applied on the images captured using the system. As the geometrical analysis eliminates the complex calibration process and rectification reduces the correspondence searching to one-dimensional, this method provides a simple stereo matching technique for this system. Experimental results are presented to show the effectiveness of the approach.

10 citations


Cited by
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Journal ArticleDOI
21 Aug 2015-Sensors
TL;DR: The experimental results show that the proposed evaluation criteria can effectively predict the visual perception of stereo capture quality for long-distance shooting.
Abstract: The realization of the Internet of Things greatly depends on the information communication among physical terminal devices and informationalized platforms, such as smart sensors, embedded systems and intelligent networks. Playing an important role in information acquisition, sensors for stereo capture have gained extensive attention in various fields. In this paper, we concentrate on promoting such sensors in an intelligent system with self-assessment capability to deal with the distortion and impairment in long-distance shooting applications. The core design is the establishment of the objective evaluation criteria that can reliably predict shooting quality with different camera configurations. Two types of stereo capture systems—toed-in camera configuration and parallel camera configuration—are taken into consideration respectively. The experimental results show that the proposed evaluation criteria can effectively predict the visual perception of stereo capture quality for long-distance shooting.

154 citations

Journal ArticleDOI
TL;DR: This review comprehensively summarizes the historical development, methodologies, strengths and weaknesses of the diffraction grating-based, prism- based, four-mirror-adaptor-based single-camera stereo-DIC techniques, and the recently proposed novel full-frame single color camera-based stereo- DIC technique for full-field 3D shape and deformation measurement.
Abstract: Single-camera stereo-digital image correlation (stereo-DIC) techniques have gained increasing attentions and demonstrated excellent prospects in the experimental mechanics community owing to their prominent advantages of cost-effectiveness, compactness, and the avoidance of the complicated camera synchronization. Using additional optical devices, e.g. a diffraction grating, a bi-prism or a set of planar mirrors, pseudo stereo images of a test sample surface can be recorded with a single camera. By correlating these stereo images using DIC, full-field three-dimensional (3D) shape and deformation can be retrieved. This review comprehensively summarizes the historical development, methodologies, strengths and weaknesses of the diffraction grating-based, prism-based, four-mirror-adaptor-based single-camera stereo-DIC techniques, and the recently proposed novel full-frame single color camera-based stereo-DIC technique for full-field 3D shape and deformation measurement. The optical arrangements, principles and calibration procedures of these single-camera stereo-DIC techniques are described in detail. Since high-speed deformation measurement is efficiently achieved by combining the single-camera stereo-DIC with one high-speed camera, single-camera stereo-DIC techniques show great potential in impact engineering, vibration and other dynamic tests.

100 citations

Journal ArticleDOI
TL;DR: A calibration-free single-lens 3D-DIC system based on a bilateral telecentric lens and a bi-prism to measure the thermal linear expansion of a ceramic plate at elevated temperatures is proposed and reasonable measurement results verify its applicability in deformation measurements, even in high-temperature environments.
Abstract: By using the principle of stereovision, 3D digital image correlation (3D-DIC) can determine the 3D morphology and deformation of a target and has been widely used in experimental mechanics as a noncontact 3D measurement technique. To eliminate the limitations of the conventional 3D-DIC system, this study proposes a calibration-free single-lens 3D-DIC system based on a bilateral telecentric lens and a bi-prism. The performance of the proposed system is verified by tests of rigid-body translation along the out-of-plane direction. As a comparison, the same rigid-body translations are measured using a single-entocentric-lens 3D-DIC system. The results show that the measurement accuracy of the proposed system is higher than that of the entocentric-lens-based one. As an application, the proposed system is used to measure the thermal linear expansion of a ceramic plate at elevated temperatures. The reasonable measurement results verify its applicability in deformation measurements, even in high-temperature environments.

65 citations

Journal ArticleDOI
Liping Yu1, Bing Pan1
TL;DR: A novel color stereo-digital image correlation (stereo-DIC) method using a single 3CCD color camera for full-field shape, motion, and deformation measurements without any sacrifice of the camera sensor spatial resolution is presented.
Abstract: This paper presents a novel color stereo-digital image correlation (stereo-DIC) method using a single 3CCD color camera for full-field shape, motion, and deformation measurements without any sacrifice of the camera sensor spatial resolution. With the aid of a specially designed color separation device using a beam splitter and two optical bandpass filters, images of blue and red colors are simultaneously recorded by the 3CCD camera from two different optical paths. The blue and red channel sub-images extracted from the recorded color images can be analyzed using the regular stereo-DIC algorithm to obtain the full-field three dimensional (3D) information of a test object surface. The effectiveness and accuracy of the proposed technique are demonstrated by a series of real shape, in-plane and out-of-plane translation, and 3D deformation tests.

57 citations

Dissertation
01 Jan 2000
TL;DR: In this paper, a biprism-stereo camera system was proposed to recover the depth of the object using only the disparity between the corresponding points. But this method requires a single camera and a biparism placed in front of the camera.
Abstract: In this paper we propose a novel and practical stereo camera system that uses only one camera and a biprism placed in front of the camera. The equivalent of a stereo pair of images is formed as the left and right halves of a single CCD image using a biprism. The system is therefore cheap and extremely easy to calibrate since it requires only one CCD camera. An additional advantage of the geometrical set-up is that corresponding features lie on the same scanline automatically. The single camera and biprism have led to a simple stereo system for which correspondence is very easy and which is accurate for nearby objects in a small field of view. Since we we only, a single lens, calibration of the system is greatly simplified. This is due to the fact that we need to estimate only one focal length and one center of projection. Given the parameters in the biprism-stereo camera system, we can recover the depth of the object using only the disparity between the corresponding points.

49 citations