Research On Depth Sensing Based On Active Stereo Vision

With the rapid development of information technology,the two-dimensional information captured by traditional cameras can't meet the needs of people.Today,how to acquire the three-dimensional(3D)information has become the mainstream developing direction,and depth sensing technology is the key to obtain 3D information.Researchers are devoted to exploring how to obtain high-speed and high-precision depth information for a long time.The structure of structured lighting depth sensing system is simple,and it can guarantee the relative high precision of the depth measurement.Therefore,structured lighting method has become the most common depth sensing methods.In the single camera and single projector structured lighting depth sensing system based on phase-shifted method,the depth of measured object can be restored by only projecting three phase-shifted fringe patterns.This method not only ensures measuring accuracy but also has excellent real-time performance.However,the relative phase can only be obtained by three phase-shifted fringe images,and the relative phase needs to be unwrapped to obtain the absolute phase.The time phase unwrapping method requires additional one or more sets phase-shifted fringe patterns with different frequency,which undoubtedly reduces the dynamic performance of the depth measurement.The spatial phase unwrapping method only needs one relative phase map to complete phase unwrapping,but it can't process the measured object with depth discontinuity.To solve the problems of time and spatial phase unwrapping,we proposed a novel phase unwrapping method.In the proposed phase unwrapping,the depth measurement can be completed by only three phase-shifted fringe patterns and one speckle pattern.Considering that the phase unwrapping of planar target is relatively simple,the structured lighting system is used to capture three phase-shifted fringe images and one binary speckle image of approximate planar target before starting formal measurement.The reference relative phase map calculated by the three phase-shifted fringe images and the reference speckle image are stored for subsequent formal depth measurement.When the formal depth measurement is started,finding the correspondences between the current speckle image and reference speckle image are similar to searching the correspondences of image pair in active stereo vision,so the matching relationship of speckle image pair is established by modified PatchMatch Stereo matching algorithm.Combined with reference absolute phase map,the rough absolute phase map of current speckle pattern can be acquired.We don't directly use the rough absolute phase map to solve depth,but use it to determine the period of the relative phase map for achieving accurate absolute phase map.Then,the relationship of phase-depth is used to solve the 3D space coordinates of measured objects.In addition,in order to meet the requirement of real-time depth sensing,the modified PatchMatch Stereo matching algorithm is parallel realized on a consumer-grade GPU(Nvidia GTX1060)based on CUDA,which can output the disparity map at 187 frame per second.To verify the effectiveness of the proposed phase unwrapping method,we have completed the depth measurements of the object with surface complex,multiple isolated objects and colorful object with rich texture.