基于相位标靶的相位测量轮廓术投影色差建模与校正

Projection chromatic aberration modeling and correction of phasemeasurement profilometry based on phase target

光学三维测量中的三通道相位测量轮廓术具有高精度、易识别、自动化程度高等优点,在科学研究和工程应用中获得了广泛的关注。在三通道相位测量轮廓术中,投影仪不同通道间的色差成为影响测量精度的关键因素。针对该问题,文中开展了基于相位标靶的相位测量轮廓术投影色差建模与校正研究。提出了将带有全息投影膜的液晶显示屏(Liquid Crystal Display, LCD)当作相位标靶对投影色差建模与校正的方法。通过LCD显示条纹与投影仪投射条纹的相位,计算投影仪色差并建立其数学模型。然后通过预补偿的方法实现投影仪三通道投射色差的校正,进行实验验证校正前后对相位测量轮廓术精度的影响。实验结果表明,文中所提方法的校正效果为蓝绿通道的平均色差由0.325 5 pixel校正为0.106 3 pixel,红绿通道的平均色差由0.365 1 pixel校正为0.111 4 pixel。该方法可为三通道相位测量轮廓术提升投影质量。实测台阶的平均误差从0.489 mm减少到0.038 mm。实验结果验证了投影仪色差建模与校正方法的有效性,提升了三通道相位测量轮廓术的整体测量精度。与已有方法相比,可以有效避免相机误差带来的影响,大大缩短计算时间,能够适用于不同型号的投影仪色差测量与校正。

Objective Due to the advantages of high precision,easy recognition and high degree of automation,the threechannel phase measurement profilometry in optical three-dimensional measurement has gained increasing attention in both scientific research and engineering applications.For three-channel phase measurement profilometry,the chromatic aberration between projector channels is the key factor affecting the measurement accuracy.Most of the existing chromatic aberration correction methods of projectors regard projectors as"reverse cameras".Therefore,the accuracy of correction results will be dependent on the imaging quality of the camera.Moreover,the existing chromatic aberration measurement and correction methods still have shortcomings,so it is significant to improve the measurement accuracy of the system.Therefore,this study carries out the research on the projection chromatic aberration modeling and correction of phase target-based phase measurement profilometry.Methods In this paper,the projection chromatic aberration modeling and correction method using the LCD screen with holographic projection film as the phase target is proposed(Fig.3).Firstly,the unfolded phase of LCD display fringes and projector projection fringes are calculated respectively.Next,binary fitting on display phase and projection phase are carried out.The green channel is regarded as an ideal channel,and the ideal pixel values of red and blue channels is calculated.Then the ideal pixel is substituted into the projection equation,and the ideal phases of the red and blue channels are obtained.Thus,the mathematical model of the chromatic aberration of the projector is established.Finally,the pre-compensation of projection fringes is implemented with the established chromatic aberration model(Fig.5).Then,the pre-compensated fringes are projected in three channels,so that the chromatic aberration of the projector is corrected.Results and Discussions The experimental results demonstrated the performance of the proposed method.The average chromatic aberration of the blue and green channels is corrected from 0.3255 pixel to 0.1063 pixel.The average chromatic aberration of the red and green channels is corrected from 0.3651 pixel to 0.1114 pixel(Fig.10).This method can effectively improve the projection quality for three-channel phase measurement profilometry.The average error of the measured step is reduced from 0.489 mm to 0.038 mm(Tab.2).The experimental results verified the effectiveness of the chromatic aberration modeling and correction method of projector.This method can improve the overall measurement accuracy of three-channel phase measurement profilometry.Compared with the existing methods,the proposed method can be calibrated to avoid the impact of camera errors and effectively shorten the calculation time.Moreover,this method can be applied to the measurement and correction of different projector chromatic aberration.Conclusions A phase-measurement contouring chromatic aberration modeling method using an LCD display as a phase target is designed and calibrated for study.This method eliminated the coupling error of the camera while measuring and calibrating the projector chromatic aberration,and enabled measurement of the projector chromatic aberration at global pixel points, while using mathematical modeling to model the projector chromatic aberrationin a chromatic way to shorten the calculation time. By measuring the 3D shape of the actual object for accuracycomparison experiments and comparing the accuracy error before and after correcting the chromatic aberration ofCP270 projector and PRO4500 projector, it can be concluded that the projection chromatic aberration modelingand correction study based on phase target proposed in this paper can better improve the projection quality inphase contour measurement and enhance the measurement accuracy of commercial projectors with poor accuracy.For the projectors with low accuracy, the method of correcting chromatic aberration in this paper can greatlyimprove the measurement accuracy of projectors. For the projectors with high accuracy, the proposed projectorchromatic aberration modeling and correction method can further improve the measurement accuracy.