Research On High Dynamic Imaging System And Its Application Based On DMD Pixel-Level Modulation

Vision measurement is one of the important contents in the field of non-contact measurement.As the core device of vision measurement--camera,its dynamic range,which is the range of brightness of the scene that the camera can record,affects the imaging quality and measurement results.Currently,the dynamic range of camera commonly used can not observe the large dynamic range scenes and highlighted industrial scenes.Therefore,how to enlarge the dynamic range of camera is a hotspot in vision measurement.In this paper,based on the research at home and abroad,Digital Micromirror Device(DMD)is selected as the spatial light modulator before imaging,and a set of high dynamic range imaging system based on DMD dimming is built,and the high dynamic range imaging method and imaging application are studied.Finally,adaptive high dynamic range imaging based on pixel-level light modulation is realized,which provides a solution to the problems of highlighted vision detection and 3d measurement.The contents in this paper are as follows:(1)Accurate pixel-level mapping between DMD and CCD.In this paper,an accurate phase mapping method based on composite phase-shifting fringe is proposed.Through the comparison experiment of coordinate mapping between DMD and CCD,the superiority of the proposed mapping method is confirmed: Compared with the traditional phase-shifting fringe mapping method,the number of phase-shifting fringe patterns required by the composite fringe mapping method is reduced by one time,and the mapping efficiency is improved.In addition,the proposed mapping method has improved its accuracy compared with previous methods,and the root mean square errors of coordinate mapping in both horizontal and vertical directions are within 0.11 pixels,reaching sub-pixel mapping accuracy.(2)The design of DMD light modulation algorithm.Based on high dynamic range imaging principle and the response relation of camera-DMD modulation in DMD imaging system,two DMD light modulation algorithms are proposed,one is based on the gray scale and another is based on adaptive modulation,in which,The image captured by DMD adaptive modulation method achieved an over-exposed pixel suppression ratio of 99%.Compared with the conventional multi-exposure method,the number of over-exposed pixels is reduced by 10 times and the image entropy is increased by nearly 10%.It can efficiently and accurately recover the over-exposed image regions with strong robustness.(3)Research on structured light 3-d measurement system and algorithm for the surface of highlighted objects.This paper set up the structured light 3-d measurement system based on DMD camera,and put forward a compensation algorithm for structured light 3-d measurement of highlighted objects based on DMD modulation.Through 3-d reconstruction and measurement of the highlighted standard sphere and metal workpiece before and after compensation,it is proved that the system and method can compensate 3-d point cloud loss caused by overexposure in structured light system,and can be further improve the measurement accuracy and broaden the application range of the 3-d structured light measurement to a certain extent.