相移法测量三维轮廓具有原理简单、计算速度快等优点。然而此法至少需要采集3幅以上干涉图像，且在实际操作中由于很难产生绝对的相移量而给测量带来误差。应用虚条纹相移算法只需要采集一幅图像便可恢复出物体的三维轮廓，其基本手段是先获得原始图像的基频值f0，根据此频率通过计算机生成具有π/2相位差的两虚条纹图像cos(2πf0x)和sin(2πf0x)。然后分别与原始图像进行混叠，将混叠后得到的图像进行低通滤波，再结合相移算法恢复出原始物体的三维轮廓。此法既保持了相移法本身的优点又解决了其需要采集多幅图像以及无法实现绝对相移的问题。另外低通滤波本身的去噪特性给在非陡变物体测量中高频噪声的去除带来方便。

It′s easier to understand in principle and faster to calculate in reconstruction by using the method of phase stepping profilometry (PSP) for three-dimensional (3-D) shape measurement. But it needs three images at least and can′t produce the absolute value of phase stepping to avoid error in practice. Virtual grating phase-shifting is proposed and it just needs one image. We first calculate or detect the base frequency f0, then use the computer to built two images by expression of cos(2πf0x) and sin(2πf0x) with π/2 phase difference. Multiply the images with original image separately, we filter the images with low pass filter and reconstruct the 3-D profile of original object by using PSP algorithm. This method reserves the advantage of PSP, solves the shortcoming of and cannot set absolute value of the phase step. In addition, the low pass filter can filter the nose of high frequency by itself, which can be used for measuring 3-D profile with non-sharp surface especially.