Research On Measurement Of Specular Objects Based On Polarization-defocused Encoded Structured Light

3D-measurement technology is significance in the field of industrial production.In order to deal with the measurement of different objects,the types of structured light measurement are varied.The measurement technology for specular objects has always attracted much attention.Therefore,the measurement of specular objects based on polarized-defocused structured light is studied in this paper.Accuracy is one of the most important criteria to evaluate the measurement system.The calibration and the structured light coding play a decisive role in the accuracy.On the one hand,the projector is a strong light projection device,and this concentration of light energy will cause strong highlights on the object surface,which seriously affects the feature point extraction in the system calibration process.On the other hand,the complex ambient light increases the noise of the image acquired by the camera,which seriously interferes with the decoding of the system and affects the accuracy.Aiming at the reflection characteristics of specular objects,a measuring system based on polarized defocusing structured light is proposed.Polarization coding technology is used in the system.The measurement system is optimized from calibration and structured light coding respectively.The main contents are as follows:(1)In the camera-projector calibration process,the calibration image is taken.The extraction of feature points is very important for calibration accuracy.Most of the current research improves the quality of images by filtering and denoising the image,enhancing the image contrast,ignoring the accuracy improvement in the process of image shooting.In this paper,a calibration method based on the global optimal polarization degree is proposed and the mathematical relationship between the pixel intensity of the image and the global optimal polarization calibration image is given.Six sets of color polarization calibration images are projected onto the calibration plate in turn.Multiple sets of calibration images are obtained.The images obtained by grouping were calibrated to calculate the reprojection error.A group of calibration images is selected,and the image with the highest reprojection error is replaced with the corresponding calibration image with the lowest reprojection error among the other five groups of images.Then,the reprojection error is calculated.This process is repeated until the reprojection error does not change,and finally a set of globally optimal polarization calibration images are obtained.This method gives full play to the polarization coding ability of LCD projector in the measuring system and reduces the error caused by the rotation of polarizer in the traditional polarization calibration technique.(2)In order to improve the robustness of the 3 system and cope with the complex and changeable environment,a polarization-defocused encoded method is proposed.The mathematical model of compound polarization degree in polarization defocusing system is established.By defocusing,the composite polarization degree of structural light and light intensity change synchronously.The information of the structured light is simultaneously encoded in the polarization parameters and light intensity parameters of the structured light by means of defocus.Compared with traditional 3D imaging technology based on light intensity,the polarized strategy provides an additional channel of information.