1. Introduction
In optical 3D sensing, techniques based on pattern-projected methods have the properties of nondestructive detection, high depth accuracy, fast measurement speed, and full-field inspection. It consists of a pattern projection system and an image acquisition system. The inspected surface is illuminated by a pattern from the projection system. Pattern distorted by the surface is recorded by the image acquisition system at a different viewpoint. With triangulation methods or suitable calibrations, distribution of the projected pattern is analyzable to retrieve the 3D shape.
One of the major studies for 3D profile measurements is the application to complicated objects, such as the inspection of a dynamic object with large depth discontinuities.Improvement of the existing projection techniques is one of the desirable solutions. The projection technique can be either the so-called structured light encoded method [1-5] or the fringe projection method [6-8]. However, both existing methods have advantages and drawbacks.
In the method of fringe projection, the distorted fringes on the tested object are evaluated to retrieve the 3D shape. Phase of the fringes can be carried out by the phase-shifting technique [8-11] or Fourier transform method [7]. In general, the phase-shifting technique takes more than three frames to evaluate the phases and therefore is more accurate than the Fourier transform method. Depth accuracy better than one part in ten thousandth of the field of view can be achieved [12-14]. Unfortunately, the longer measurement procedure makes it inefficient to detect dynamic objects. The Fourier transform method is advantageous to perform dynamic inspection since only one single-shot measurement is required. However, compared with the phase-shifting technique, the accuracy is relatively worse. In addition, both the phase-shifting technique and Fourier transform method involve the arctangent operation.
Thus, the extracted phases have principle values ranging from –π and π, and have discontinuities with 2π phase jumps. A so-called phase unwrapping process to recover the absolute phase is inevitable. When objects of interest have large discontinuous height steps, the height steps hinder the unique assignment of fringe order, resulting in ambiguity of phase unwrapping.
求大哥大姐们无聊的时候帮下忙,分不多~~
最好不是软件翻译的~起码要读的通呀- -