为避免多级灰度值编码所带来的非线性问题,并进一步提高测量速度和适应性,提出了一种二元阶梯相位编码方法。首先,利用传统N步相移法,投影若干幅正弦光栅条纹到待测物体表面,接着投影若干幅相移条纹对应的采用二值化编码的条纹;在通过四步相移法求得光栅条纹的包裹相位后,利用二值编码条纹解调后得到的阶梯相位,确定光栅条纹的周期级次;最终根据周期级次对包裹相位进行解包裹得到绝对相位,完成相位去包裹。利用二值化条纹进行阶梯相位编码的方法,克服了传统阶梯相位编码方法使用多级灰度值引起的非线性问题。实验结果表明,以单通道投影图像数目为标准,在同等条件下,与已有的同类方法相比,本文方法的测量速度提高了12.5%,且适应性强,能够有效地进行物体的三维形貌测量。
In order to avoid the nonlinear problem caused by multilevel gray value coding, and to improve the speed and the adaptability of the measurement, a new method of binary encoding is proposed to get the stair phase. First of all, using the traditional N-step phase shift method,a number of sinusoidal grat- ing fringes are projected onto the surface of the object to be measured,and then a number of binary cod- ing fringes are projected onto the tested objects. After the wrapped phase is obtained through a four-step phase-shifting method, by using the stair phase got from the binary encoded fringe demodulation, the grating period orders are determined, the wrapped phase is unwrapped according to the periodic orders, and eventually the absolute phase is obtained. The method of using binary fringes to encode stair phase has overcome the the nonlinear problem. Experimental results show that with a standard of the number of single channel image projection, and under the same conditions, the measurement speed is enhanced by 12.5% compared with that of existing method. The method is efficient for the 3D shape measurement of objects.