新的基于条纹投影轮廓测量的系统标定方法

提出一种新的光栅条纹投影轮廓测量术系统标定模型,新模型不要求投影装置和成像系统的光心连线与参考面平行、成像系统的光轴垂直于参考面及投影装置和成像系统的光轴相交。基于该模型得出了新的相位高度映射关系,其待定系数与成像点的坐标无关。实际测量中只需2个高度不同的标准块便可以求得待定系数。对4个标准块进行高度测量,得到的最大相对误差为06%。实验证明:该标定方法简单有效,提高了系统标定的可操作性和测量精度。     

新的基于条纹投影轮廓测量的系统标定方法

提出一种新的光栅条纹投影轮廓测量术系统标定模型,新模型不要求投影装置和成像系统的光心连线与参考面平行、成像系统的光轴垂直于参考面及投影装置和成像系统的光轴相交。基于该模型得出了新的相位高度映射关系,其待定系数与成像点的坐标无关。实际测量中只需2个高度不同的标准块便可以求得待定系数。对4个标准块进行高度测量,得到的最大相对误差为0.6%。实验证明:该标定方法简单有效,提高了系统标定的可操作性和测量精度。     

基于两步标定法的稳定、高精度条纹投影三维轮廓重建北大核心CSCD

在传统的条纹投影轮廓术(FPP)重建算法中,通常倾向于简化校准模型以提高数值稳定性。但是简化后的校准模型难以有效地补偿FPP系统中照相机和投影仪的镜头畸变,结果不能保证FPP的测量精度。提出了一种两步标定法,依次执行镜头畸变补偿和系统标定,通过使用相机和投影仪的标定参数来校正输入变量的值,实现镜头畸变的有效补偿,同时给出形式简洁但精度更高的测量模型进行物体三维轮廓重建。实验结果验证了方法的有效性和实用性。     

一种新的基于条纹投影的三维轮廓测量系统模型

提出一种新的光栅条纹投影轮廓测量术系统模型,新模型不要求测量系统满足光心连线平行于参考面、成像系统光轴垂直于参考面以及两光轴相交于参考面上等约束条件,只需投射至参考平面的正弦光栅条纹之间相互平行,简化了系统校准过程,有利于现场测量。得到的高度相位映射关系式中,待标定的系数与像点的坐标无关,不需要对每一个像点进行采样,能够减少系统标定所需的时间。实验表明:所提方法使投影装置和成像系统的位置校准过程简单,提高了系统标定的速度,且具有较高的测量精度,能够测量复杂面形的物体,增强了光栅投影三维测量系统的实用性。     

基于双色条纹投影的快速傅里叶变换轮廓术

在实际傅里叶变换轮廓术测量中，获取的条纹图扩展的零频分量对傅里叶变换轮廓术的测量精度和测量范围有很大影响，甚至妨碍正确三维面形的恢复。π相移技术常被用来消除零频分量对测量的影响，但需要在测量系统中安装精密相移装置，并需要采集两帧具有π相位差的条纹图。传统傅里叶变换轮廓术中，完成精密相移需要较长的时间，影响了傅里叶变换轮廓术测量方法的实时性。提出了采用双色正弦光栅投影来实现从一帧条纹图中消除零频对傅里叶变换轮廓术测量的影响。该方法同传统的π相移方法相比，不需要相移装置，测量系统简单，并且能真正实现高速测量。     

单周期条纹双四步相移投影仪的标定方法

针对投影仪标定方法中存在畸变及倾斜投影引起条纹周期、条纹级数变化的问题,提出一种单周期条纹双四步相移投影仪的标定方法.设计生成横向和纵向各两组单周期条纹图像,经投影仪投影到带有圆形标识的标定板上,相机同步采集标定板图像,叠加由双四步相移获得的两幅相位主值图,对叠加相位主值图相位展开,利用展开的绝对相位值计算投影仪像素坐标值,最终将投影仪标定转换为成熟的相机标定.实验结果表明:仿真投影仪标定实验准确度的最大重投影误差约为0.4pixel,均方根误差为0.132 96pixel;实际投影仪标定实验准确度的最大反投影误差约为0.46pixel,均方根误差为0.143 12pixel;实验结果与仿真结果的最大反投影误差相差15%,均方根误差相差7.6%.与现有的采用三频相位展开进行投影仪标定的方法相比,投影光栅图像数可减少8幅.该方法改善了现有投影仪标定方法的不足,标定准确度和标定效率均得到提高.     

基于立方体分光棱镜的干涉投影傅里叶变换轮廓术

提出了一种基于立方体分光棱镜的干涉投影傅里叶变换轮廓术。基于杨氏双缝干涉原理,对立方体分光棱镜的干涉投影理论进行理论分析和仿真实验,通过调节立方体分光棱镜的安装角度可实现干涉投影条纹周期的任意调节,结果证实了该干涉投影系统的可行性以及灵活性。对小脚丫模型进行了三维面形重构,结果表明:干涉条纹相位稳定且强度分布均匀,利用所提方法可以很好地恢复物体的三维形貌。     

基于双频彩色条纹投影的相位测量去包裹方法

为了提高测量速度,提出一种基于双频彩色条纹投影的相位测量去包裹方法,只需采集一帧图像,就能实现高速测量以及动态物体轮廓测量中的相位去包裹。论述了双频相位测量和变精度去包裹原理,并详细分析影响测量精度的因素。该方法采用计算机生成一帧双频双色正弦条纹图,用液晶数字投影仪投影,并用傅里叶变换的方法对两个单色条纹图进行分析,获得高低两种精度的被测物体高度信息,从而进行变精度去包裹处理。结果表明,利用该方法提高了测量速度,可得到较高的去包裹精度,其测量最大绝对误差为 1．413～-1．582 mm,标准差为0．363 mm。     

Innovative calibration technique for fringe projection based 3D scanner

A new approach to 3D scanners calibration, based on Fourier Transform Profilometry method, is proposed and verified by experiments. Commonly used calibration techniques require that a calibration plane is placed in different and known positions in the scanner measuring volume; an optimization procedure iteratively change the value of some calibration parameters in order to minimize the discrepancy between the height distributions of the measured planes and the reference ones. The main limit of this type of calibration techniques is the necessity to guarantee a high accuracy in the placement of the planes used as calibration references. The innovation of the method proposed in this paper is the complete removal of any device for the accurate plane placement by assigning the task of the plane positions estimation to the camera, which is part of the scanner. The well known camera calibration algorithm proposed by Zhang permits at the same time to calibrate the camera and to estimate the positions and orientations of the plane used for the calibration itself. The knowledge of the plane position allows to use them as a reference of the scanner calibration. The obtained results show that this method provides accuracy values for the scanner parameters estimation comparable with other calibration techniques, but the advantage is that no particular device is needed.     

数字条纹投射技术中改进的非线性校正方法

在数字条纹投射技术中,系统的非线性是影响投射条纹质量的主要因素,其直接导致变形条纹中出现高次谐波,从而影响系统的测量精度。提出了一种系统非线性校正的新方法,利用N阶多项式拟合代替传统的单一伽马参数表示系统的非线性关系,并依据条纹图像累积直方图匹配方法,通过迭代操作同时求得系统非线性关系和较高精度的物体位相分布。计算机模拟及实验结果表明,该方法能够有效地抑制系统非线性的影响,获得理想的物体位相分布,从而验证了该方法的可行性。     

Least-squares calibration method for fringe projection profilometry with some practical considerations

Fringe projection profilometry (FPP) is a widely used three-dimensional profile measurement technique. One vital step in this technique is calibration, which determines the system accuracy. The least-squares method, because of its flexibility and simplicity, is commonly used in system calibration for FPP. However, calibration results are affected by the nonlinear gamma of the projector and projection fringe cycle broadening. This paper proposes a new look-up table (LUT) generation method by analyzing the differences between the real and ideal unwrapped phases. The aforementioned problems could then be solved after the phase error is compensated by the LUT. Finally, the validity of the proposed method is demonstrated through experiments, and the accuracy reaches 0.02 mm.     

Period correction method for binary fringe defocused projection

Binary fringe defocused projection can resolve the problem caused by the nonlinear gamma of the projector. Owing to the intersecting axis measurement system, the broadening of the fringe period on the reference plane can cause measurement errors. Non-uniform periodical binary fringe defocused projection is utilized to overcome this problem. After appropriate defocused projection of non-uniform periodical binary fringe, uniform periodical sinusoidal fringe can be obtained on the reference plane. This method can prevent the nonlinear gamma effect and broadening of the fringe period, and filter high harmonics and high-frequency noise. Three-dimensional (3-D) shape measurement experiments of standard flat are performed with four-step phase-shift method. Experimental results demonstrate that the proposed method exhibits high measurement precision. Highly accurate 3-D measurements of large objects can also be performed with the proposed method.     

Flexible digital projector calibration method based on per-pixel distortion measurement and correction

When a digital projector is applied in high precision applications, the intrinsic parameters and distortion characteristics should be calibrated precisely. In this paper, a flexible full-field projector calibration method is proposed without any approximate distortion model. With planar homography theory and fringe projection technique, the projector distortion characteristic on each pixel can be measured independently and an initial distortion map is generated. The intrinsic parameters are calibrated afterwards. Then, the initial distortion map can be refined by correcting the non-perpendicularity between the optical axis and image plane. The original pattern to be projected is corrected with the refined distortion map. Thus, the calibrated projector can be regarded as an ideal projector conforming to the pinhole model. Experimental results show a nearly ideal residual map for the corrected projection pattern. In addition, the proposed calibration method is flexible without any sophisticated ancillary equipment or complicated procedure.     

A study on carrier-removal techniques in fringe projection profilometry

This paper describes a comparison of several carrier-removal techniques normally used in fringe projection for surface shape measurement. The performance of various algorithms, including the necessity for manual intervention, the complexity in data recording, and the side effect on measurement accuracy, is evaluated. The applicability of nonlinear carrier removal and the restrictions on the direction of carrier fringe in various algorithms are also investigated in this paper. It is also shown that an advanced algorithm is able to achieve carrier removal with minimal manual intervention and significantly simplify the calibration process of a fringe projection system.     

基于投影栅线法测量物体三维轮廓的一点改进

研究了利用投影栅线法测量光滑鼠标的三维轮廓。对传统的傅里叶变换轮廓术提出了一点改进,在傅里叶变换之后,不对频谱部分频移,而是直接滤出需要的高、低频部分,再分别进行傅里叶逆变换,就可以得到与高度有关的相位差。该方法与传统的方法相比,减少了3次频移的过程,大大减少了计算量,也提高了滤波的精度。实验结果表明:只需要0.1 s就可以完成测量过程,测量精度达到0.2 mm, 可以成功实现光滑物体的三维轮廓测量。     

A 3D shape retrieval method for orthogonal fringe projection based on a combination of variational image decomposition and variational mode decomposition

The orthogonal fringe projection technique has as wide as long practical application nowadays. In this paper, we propose a 3D shape retrieval method for orthogonal composite fringe projection based on a combination of variational image decomposition (VID) and variational mode decomposition (VMD). We propose a new image decomposition model to extract the orthogonal fringe. Then we introduce the VMD method to separate the horizontal and vertical fringe from the orthogonal fringe. Lastly, the 3D shape information is obtained by the differential 3D shape retrieval method (D3D). We test the proposed method on a simulated pattern and two actual objects with edges or abrupt changes in height, and compare with the recent, related and advanced differential 3D shape retrieval method (D3D) in terms of both quantitative evaluation and visual quality. The experimental results have demonstrated the validity of the proposed method.