Comparison of the squared binary, sinusoidal pulse width modulation, and optimal pulse width modulation methods for three-dimensional shape measurement with projector defocusing

Abstract

This paper presents a comparative study on three sinusoidal fringe pattern generation techniques with projector defocusing: the squared binary defocusing method (SBM), the sinusoidal pulse width modulation (SPWM) technique, and the optimal pulse width modulation (OPWM) technique. Because the phase error will directly affect the measurement accuracy, the comparisons are all performed in the phase domain. We found that the OPWM almost always performs the best, and SPWM outperforms SBM to a great extent, while these three methods generate similar results under certain conditions. We will briefly explain the principle of each technique, describe the optimization procedures for each technique, and finally compare their performances through simulations and experiments. Disciplines Computer-Aided Engineering and Design | Mechanical Engineering CommentsThis article is from Applied Optics 51 (2012) This paper presents a comparative study on three sinusoidal fringe pattern generation techniques with projector defocusing: the squared binary defocusing method (SBM), the sinusoidal pulse width modulation (SPWM) technique, and the optimal pulse width modulation (OPWM) technique. Because the phase error will directly affect the measurement accuracy, the comparisons are all performed in the phase domain. We found that the OPWM almost always performs the best, and SPWM outperforms SBM to a great extent, while these three methods generate similar results under certain conditions. We will briefly explain the principle of each technique, describe the optimization procedures for each technique, and finally compare their performances through simulations and experiments.

Toward superfast three-dimensional optical metrology with digital micromirror device platforms

“…These techniques each work to improve the phase quality, yet they too still face their own issues: especially if the stripes in the fringe images are either too narrow or too wide. 36 Given the discrete nature of these fringe patterns, however, there might not be many improvements that can be made in this regard. It should be stated that these PWM developments are all one-dimensional.…”

Three-dimensional shape measurement with binary dithered patterns

“…The binary defocusing technique has many potential advantages: (1) no requirement for gamma calibration since only two grayscale values are used [9], (2) no strict requirement for camera exposure time even when the digital-light-processing (DLP) projector is utilized [10], and (3) possibilities of achieving unprecedentedly high-speed 3D shape measurement [11]. However, the binary defocusing technique is not trouble-free, especially when the fringe stripes are wide where the high-order harmonics cannot be effectively suppressed by defocusing due to the limitation of the projector lens [4]. Dithering, which is one technique used to achieve satisfactory image rendering and color reduction, has the potential to tackle the aforementioned problem of the squared binary technique.…”

“…Yet, it is very difficult for them to produce high-quality 3D shape measurement when the fringe stripes are wide and when the projector is nearly focused [4]. This is because for the binary defocusing techniques, binary patterns are fed to the projector and sinusoidal patterns are generated by properly defocusing the projector.…”

Improve dithering technique for 3D shape measurement: phase vs intensity optimization

“…Though successful, such techniques fails to substantially improve the measurement quality when fringe stripes are very wide. 13 Taking advantages of the 2D nature of the structured patterns, area-modulation method could further improve the binary defocusing method, [10][11][12] with the dithering-based techniques being the most promising for DFP systems due to their varieties and accuracy. Furthermore, the dithering techniques could be further optimized for phase-based DFP systems.…”