Profile Measurement Of Low Signal To Noise Ratio Targets Based On Laser Lock-in Imaging

In actual industrial productions, there have been a large number of mirror objectives and objectives with strong background light needed to be three-dimensional shape measurement, such as polished mold target, auto body surface, hot billets, and rail trucks. The current measurement techniques on such goals can be divided into manual measuring method and the three-dimensional measurement method based on optics. Manual measurement is valid only for some categories of target, a low efficient method, and complicated. The three-dimensional measurement based on optics is feasible only for diffuse targets. For polished targets such as mirror targets or targets with strong background light, the optical measurement method is significant only as the camera sensor, the light source and the target under test are positioned on the optical path, which leads to the measuring equipment is more complicate.The difficulty to measure a mirror objective and the objective with strong background light is that the signal to noise ratio of image is too low. It is difficult to directly extract the feature information of images. Based on this topic we put forward laser lock-in imaging, in combination with Piecewise linear image enhancement. The laser lock-in imaging is a way to filter out the environment light around target under test, reduce the noise in the image. After completion of the laser lock-in imaging, the image of superposition and filtering, signal-to-noise ratio within a certain can be improved significantly. Piecewise linear enhancement for orientation of characteristic information of the image enhancement, which improves the Signal to Noise Ratio of image further. Because it is impossible to determine the enhanced image feature information in grayscale,it is needed to adopt OTSU for binary images. To extract feature information of images, this topic is based on Delaunay triangle subdivision splicing triangles and eventually to restore three-dimensional surface shape of the object under test, and finally with the help of OpenGL to display three-dimensional surface shape of objects.This thesis put forward laser lock-in imaging in combination with Piecewise linear image enhancement. This technique has a characteristics that does not require the camera sensor, the position of the light source and the target to be placed in the optical path.