Product name:3D Reconstruction

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Three-dimensional reconstruction
Open classification: 3D computer graphics, medical terms, computer terms, computer science and technology terms
The English term name for 3D reconstruction is 3D Reconstruction. 3D reconstruction refers to the establishment of mathematical models suitable for computer representation and processing of 3D objects. It is the basis for processing, manipulating, and analyzing its properties in a computer environment. It is also established in computers. Key technologies for expressing the objective world of virtual reality. In computer vision, three-dimensional reconstruction refers to the process of reconstructing three-dimensional information from single-view or multi-view images. Because the information of a single video is incomplete, three-dimensional reconstruction requires the use of empirical knowledge. Multi-view three-dimensional reconstruction (similar to the human double (Eye positioning) is relatively easy. The method is to first calibrate the camera, that is, calculate the relationship between the camera's image coordinate system and the world coordinate system. Then use the information in multiple two-dimensional images to reconstruct three-dimensional information.
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table of Contents
· 1 Introduction
· 2 steps
· 3D reconstruction method
· Stereoscopy ...
· Chroma forming method (Shapefrom ...
· Stereo Optics (Photometr ...
· Contour method
4 user assistance
3D Reconstruction-Introduction
The English term name for 3D reconstruction is 3D Reconstruction.
Three-dimensional reconstruction refers to the establishment of mathematical models suitable for computer representation and processing of three-dimensional objects. It is the basis for processing, manipulating, and analyzing its properties in a computer environment. It is also the key technology for establishing a virtual reality that expresses the objective world in a computer.
In computer vision, three-dimensional reconstruction refers to the process of reconstructing three-dimensional information from single-view or multi-view images. Because the information of a single video is incomplete, three-dimensional reconstruction requires the use of empirical knowledge. Multi-view three-dimensional reconstruction (similar to the human double (Eye positioning) is relatively easy. The method is to first calibrate the camera, that is, calculate the relationship between the camera's image coordinate system and the world coordinate system. Then use the information in multiple two-dimensional images to reconstruct three-dimensional information.
Object 3D reconstruction is a common scientific problem and core technology in the fields of computer-aided geometric design (CAGD), computer graphics (CG), computer animation, computer vision, medical image processing, scientific computing and virtual reality, and digital media creation. There are two main methods for generating three-dimensional representations of objects in a computer. One is the use of geometric modeling software to generate three-dimensional geometric models of objects under human control through human-computer interaction, and the other is to obtain the geometry of real objects through certain means. The former technology has been very mature. Several existing software support, such as: 3DMAX, Maya, AutoCAD, UG, etc., they generally use curves and surfaces with mathematical expressions to represent geometric shapes. The latter is generally called the three-dimensional reconstruction process. The three-dimensional reconstruction refers to the mathematical process and computer technology of recovering three-dimensional information (shape, etc.) of an object using two-dimensional projection, including data acquisition, pre-processing, point cloud stitching, and feature analysis.
3D reconstruction-steps
Steps for 3D reconstruction
(1) Image acquisition: Before performing image processing, first acquire a two-dimensional image of a three-dimensional object with a camera. The lighting conditions and the geometric characteristics of the camera have a great impact on subsequent image processing.
(2) Camera calibration: The camera calibration is used to establish an effective imaging model, and the internal and external parameters of the camera are solved. In this way, the 3D point coordinates in space can be obtained by combining the image matching results, thereby achieving the purpose of 3D reconstruction.
(3) Feature extraction: Features mainly include feature points, feature lines and regions. In most cases, feature points are used as matching primitives, and the form in which feature points are extracted is closely related to the matching strategy. Therefore, it is necessary to determine which matching method to use when extracting feature points.
Feature point extraction algorithms can be summarized as three methods based on directional derivatives, methods based on contrast relationships of image brightness, and methods based on mathematical morphology.
(4) Stereo matching: Stereo matching refers to establishing a correspondence relationship between image pairs according to the extracted features, that is, one-to-one correspondence between imaging points of the same physical space point in two different images. When performing matching, pay attention to the interference of some factors in the scene, such as lighting conditions, noise interference, scene geometry distortion, surface physical characteristics, and camera characteristics.
(5) Three-dimensional reconstruction: With more accurate matching results, combined with the internal and external parameters of the camera calibration, three-dimensional scene information can be restored. Because the accuracy of 3D reconstruction is affected by factors such as matching accuracy, internal and external parameter errors of the camera, etc., the first few steps need to be done first, so that the accuracy of each link is high and the error is small, so that a more accurate stereo vision can be designed. system.
3D reconstruction-3D reconstruction method
Stereoscopic
Traditional stereo imaging systems use two cameras placed together to look at the object to be reconstructed in parallel. This method is conceptually similar to how humans estimate the depth by overlapping images perceived by both eyes (of course, the human brain ’s perception of depth information is much more complicated). If the distance and focal length of two cameras are known, the intercepted The left and right pictures can be superimposed successfully, and the depth information can be quickly pushed. This method relies on effective image correlation analysis, which is generally achieved by using block matching or epipolar geometry algorithms.
Stereo vision using two cameras is also called binocular, and trinocular and other extension methods using more cameras.
Chroma Shaping (ShapefromShading)
Earlier, scholars such as B.K.P.Horn proposed that the brightness value of image pixels is substituted into a pre-designed chroma model to solve, and the solution of the equation is depth information. Since there are more unknowns in the equations than constraints, the scope of the solution set must be narrowed by more assumptions. For example, adding surface differentiability (curvature constraint), smoothness (smoothness), and more constraints to obtain accurate solutions. After this method, Stereo Optics was derived from Woodham.
Stereo Optics (PhotometricStereo)
To compensate for the lack of information provided by a single photo in the photometry method, the stereo optics method uses a camera to take multiple photos. The shooting angles of these photos are the same, and the difference is the lighting conditions of the light. The simplest stereo optics method uses three light sources to illuminate the object from three different directions, turning on only one light source at a time. After the shooting is completed, three photos are synthesized and the perfect diffusion model in optics is used to solve the gradient vectors of the surface of the object. After the integration of the vector field, a three-dimensional model can be obtained. This method is not suitable for objects that are smooth and not close to Lambertian surfaces.
Contour method
This method uses a series of objects to form a three-dimensional shape. When part of the surface of the object cannot be displayed on-line, the 3D information will be lost after reconstruction. The common method is to place the object under test on a motorized turntable, take a picture of it after rotating a small angle each time, and then remove the background and remove the contour lines through image processing techniques. After collecting the contour lines at various angles, you can "scratch" Into a three-dimensional model.
3D reconstruction-user assisted
In addition, some methods require users to provide information during the reconstruction process, and rely on the unique properties of the human visual system to assist in completing the reconstruction process.
These methods are based on the principle of photo photography, taking images of the same object to estimate three-dimensional information. Another similar method is panoramic reconstruction (panoramic reconstruction), which is to capture the surrounding image at a fixed point to reconstruct the scene environment.

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