Object Shape Measurement Based on Brox Optical Flow Estimation and Its Correction Method

Abstract

In this work, a new method of measuring surface shape based on Brox optical flow estimation is presented. The measuring system consists of a projector, a measured object and a charge coupled device (CCD) camera. The grating fringes are projected onto the reference plane at a small angle. Two fringe images—before and after placing the measured object on the reference plane—are captured, respectively. Then, the optical flow field between two images is evaluated by using Brox optical flow algorithm. The theoretical relationship between the optical flow field and the height of the measured surface is established. According to the relationship, the height distribution of the measured object can be retrieved quickly without phase-to-height transformation. However, the calculated height distribution has been found to be deviated from its true value. To solve the problem, a correction scheme suitable for the optical flow method is proposed. By using the correction scheme, the accuracy of the calculated result is greatly improved. Simulations and experiments are completed to verify the feasibility of the proposed method and the accuracy of the correction method. The results show that the proposed method is more accurate than that of the Fourier transform method. Compared with traditional surface shape measurement, the optical flow method has some obvious advantages: (1) Only two frame images are required to recover the height distribution. (2) Relatively simple in measurement process and calculation so less time consuming. (3) Because the optical flow method contains time factor itself, it is more suitable for dynamic measurement. (4) No restrictions on projection pattern.

Image Spherizing-Based Three-Dimensional Displacement Measurement Technique for Microscope with Single Camera

“…In accord with the ordinary slope model, we can see from Figur that there is an intensity shift along the diagonal direction after deformation and the s reach minimum and maximum at the nadir and vertex of the diagonal line. In order to obtain more reliable results, we utilize gradient-based DIC method and Brox OF method [15] to extract the in-plane displacement field between Figure 5 In order to obtain more reliable results, we utilize gradient-based DIC method [13] and Brox OF method [15] to extract the in-plane displacement field between Figure 5a,b. Subsequently, the out-of-plane displacement can be calculated by Equations ( 1)-( 5).…”

“…It can be seen from the whole process that the key to achieve three-dimensional displacement extraction is the in-plane displacement estimation. Because DIC method [13] and optical flow (OF) method [15] are mature and robust in-plane displacement measurement techniques, in order to ensure the accuracy of three-dimensional displacement measurement, we utilize these two methods to estimate in-plane displacement in computer simulation experiments and application experiments, respectively. The absolute errors of out-of-plane displacement measurement results in all experiments are smaller than 0.2 µm, which proves the effectiveness of the new method.…”

Rapid Calibration of the Projector in Structured Light Systems Based on Brox Optical Flow Estimation

“…Although only two images are used for projector calibration, all pixels in the captured images can be used as effective information points, by which the projector calibration is of high accuracy. By using the calibrated coordinates of the camera and the projector, the height distribution of a measured object can be obtained efficiently [23,24].…”

“…The optical flow method is widely used to obtain the motion information of moving objects with the advantages of simple operation and strong robustness to noise [20][21][22]. When utilizing it to retrieve the height distribution of an object, the information of the measured surface shape can be obtained directly only using one deformed fringe pattern without phase-to-height operation [23,24].…”