复杂物体的快速三维测量是光学三维轮廓术的难题之一。提出了基于调制度比的光学三维测量新方法，设计了基于共轴光路的测量系统。理论分析表明，在几何光学近似下，物体表面一点调制度比的对数与该点的高度成正比，因此可以用调制度比作为物体高度的载体。通过标定建立高度与调制度比的查找表，测量时利用CCD在两个不同的位置分别获取物体表面的光栅信息，利用傅里叶变换方法计算相应物点的调制度并计算比值，根据调制度比值通过查找表得到相应物点的高度信息。该方法采用共轴光路，有效避免了阴影和遮挡问题; 采用调制度比作为物体高度测量的载体，只需要两幅光栅图就可以得到物体的高度信息，具有测量快速的优点。对高为79.51 mm的台阶测量的相对误差为0.86%，实验结果证实了该方法和系统的有效性。

It is difficult to measure a complex object with a deep hole quickly by traditional three-dimensional (3D) profilometry, such as phase measurement profilometry or Fourier transform profilometry. A new 3D profilometry based on fringe modulation ratio is presented and a coaxial measurement system is designed. It is proved that the fringe modulation ration instead of phase can be used to determine the height distribution of the object because the height of a point of the object is proportional to the log value of modulation ratio of the point. A look-up table of height and modulation ratio is established through system calibration. To obtain the height map of the object, a sinusoidal grating pattern is projected onto the surface of a testing object. Two fringe images of the object are captured by CCD at two different positions. Modulation ratio is computed by Fourier analysis and the height of the point can be obtained by look-up table. The proposed 3D measurement technique can perform 3D shape measurement fast without suffering shading problem. The relative error of the measurement of a step with 79.51 mm height is 0.86%. Experimental results demonstrate that the proposed scheme can be useful for 3D shape measurement.