Abstract
In this paper, we propose a new single-shot three-dimensional (3D) measuring method based on quaternary grating projection. In traditional binary grating phase measuring profilometry (PMP), a multi-step or color fringe pattern are usually used to extract the sinusoidal fringes. In our proposed method, by using the DLP4500’s 2-bit gray coding mode, the grayscale is quaternary. The three non-zero grayscales cyclically arranged in equal width, and the fourth grey value is 0 which is not encoded in the fringe pattern but represents the shadow information in the deformed pattern, where a quaternary grating is encoded. When the DLP4500 projects the quaternary grating onto the measured object, the charge coupled device (CCD) captures the corresponding deformed pattern synchronously. Three frames of binary deformed patterns with 1/3 duty cycle and a relative displacement of 1/3 period can be decomposed by the segmentation algorithm proposed in this paper. Three sinusoidal deformed patterns with a 2π/3 shift-phase can be obtained by extracting the fundamental frequency of the three binary deformed patterns correspondingly, and the 3D shape of the object can be reconstructed by PMP. Experimental results show the effectiveness and feasibility of the proposed method. Because the DLP4500 only needs 2-bit coded grating for projection, the refresh rate of the projected grating is as high as 1428 Hz, which will have a broad application prospect in real time and fast online measurement.
Highlights
In recent years, optical three-dimensional (3-D) shape measurement based on grating or fringe techniques has been widely used in machine vision, face recognition and product inspection with the good performance of high accuracy, high measurement efficiency, whole-field analysis and noncontact [1,2,3,4,5,6,7]
The Fourier transform profilometry (FTP) [16] proposed by Takeda et al in 1983 uses a sinusoidal grating to obtain a single frame of a sinusoidal deformed pattern for real-time measurement, but its accuracy is limited by spatial frequency domain filtering
Single-shot color profilometry [15] is performed by projecting a frame of color composite grating and the three phase-shifting sinusoidal fringes are encoded in the red (R), green (G), and blue (B) channels, respectively, to obtain the deformed patterns modulated by the object and separate them from the R, G, and B components
Summary
Optical three-dimensional (3-D) shape measurement based on grating or fringe techniques has been widely used in machine vision, face recognition and product inspection with the good performance of high accuracy, high measurement efficiency, whole-field analysis and noncontact [1,2,3,4,5,6,7]. Single-shot color profilometry [15] is performed by projecting a frame of color composite grating and the three phase-shifting sinusoidal fringes are encoded in the red (R), green (G), and blue (B) channels, respectively, to obtain the deformed patterns modulated by the object and separate them from the R, G, and B components. Fu [27] et al proposed a real-time 3D surface PMP based on color binary gratings, in which three monochromatic binary fringes occupy 1/3 period, respectively, and when arranged periodically, these binary fringes are encoded in red (R), green (G), and blue (B) channels, and the sinusoidal is directly extracted from the encoded binary grating without defocusing projection and using a proper filtering operation in spatial frequency domain. If the higher frame capturing rat a monochrome camera is used, it will have a broad application prospect in real‐time an fast online measurement
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