Research On 3D Measurement Technology Of High Dynamic Range Surface Based On Structured Light

Three dimensional measurement has important applications in industrial production and other fields.With the development of digital projection technology,structured light 3D measurement technology has gradually become the mainstream 3D measurement technology with the advantages of non-contact and high precision.In the structured light measurement system,the projector is used as the active light source,and the camera collects the image of the measured object and calculates the three-dimensional information.Therefore,the image quality of camera is an important part of 3D measurement.In the measurement,when the object has a high dynamic range surface with large reflectivity difference,the smooth surface will produce specular reflection,resulting in image highlight,resulting in overexposure of high reflection area in the image;while the low reflectivity area is beyond the dynamic range of the camera,resulting in poor image quality,loss of surface information,and shadow loss The measurement accuracy is improved.Therefore,the high dynamic range surface 3D measurement technology based on structured light is studied in this paper.In this paper,polarization and multi exposure methods are introduced into the structured light measurement system to improve the image quality.The main contents of this paper are as follows:(1)Aiming at the problem of specular reflection on high dynamic range surface,which causes image highlight to affect imaging,this paper adopts polarization method.According to the linear polarization characteristics of specular reflection light satisfying Fresnel formula,a normalized weighting algorithm is proposed.The acquisition camera images and synthesizes in multiple polarization angles.The experiment results proved that image highlight is weaken and image signal-to-noise ratio is improved.(2)Aiming at the problem that the high dynamic range surface is beyond the dynamic range of the camera when imaging,resulting in partial over exposure and under exposure of the image,which affects the measurement accuracy,a fast determination method of exposure time is proposed.This paper analyzes the object surface reflection model and camera response function,fitting the function between image gray value and object surface reflection coefficient,camera parameters and light intensity.Only two pictures need to be processed to quantify the reflection characteristics of the object surface,which provides a basis for determining the exposure time.At the same time,the concept of normal distribution is introduced to calculate the expected values of images corresponding to different exposure times,and an optimal exposure time is determined.The experiment results proved the proposed method can quantify the reflection characteristics of the object surface simply and quickly,so as to select the corresponding exposure time according to different reflectivity,which improves the disadvantage that the multi exposure method can only acquire multiple exposure time images by empirical method.(3)In order to verify the feasibility of the measurement method studied in this paper.In this paper,a structured optical measurement system based on Gray code coding is built.In the experiment,the polarization method is used to weaken the image highlight,quantify the reflection characteristics of the surface of the object under test and calculate the optimal exposure time.Finally,the 3D reconstruction of the object is realized.The experimental results show that the method proposed in this paper is simple to operate,the system is easy to build,and the speed and accuracy of the method are effectively improved.