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首页> 外文期刊>Optical engineering >Combined defocusing triangular pulse width modulation fringe pattern and Gray code for absolute phase measurement
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Combined defocusing triangular pulse width modulation fringe pattern and Gray code for absolute phase measurement

机译：组合散焦三角脉冲宽度调制条纹图案和绝对相位测量的灰色码

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摘要

Projecting defocused binary pattern method can overcome the nonlinear gamma effect of the projector, as well as filter high harmonics, but it is sensitive to defocus levels. Therefore, it makes it difficult to generate both comparable performance to ideal sinusoidal fringe patterns and good quality Gray code when only a small number of phase shift patterns are used. To overcome this problem, a phase unwrapping approach combined Gray code with phase-shifting fringe patterns generated by triangular pulse width modulation (TPWM) technique based on slight defocusing is proposed. The phase is retrieved using a four-step phase-shifting method, and the corresponding phase order is obtained by Gray-code patterns. Because of defocusing projection, the boundaries of two adjacent Gray-code patterns become blurred, which make the recovery of accurate Gray-code patterns difficult. To solve this problem, we propose to project an all-white pattern and an all-black pattern to obtain threshold values, which are used to execute the binarization of Gray-code patterns. This approach is robustness to different defocus levels of projector. Experiments are submitted to verify that the proposed technique can be utilized to high-accuracy three-dimensional shape measurement of complex and/or discontinuous objects.
机译：投影散焦二元图案方法可以克服投影仪的非线性伽马效果，以及滤波器高谐波，但对散焦水平敏感。因此，当仅使用少量相移图案时，它使得难以为理想的正弦条纹图案和良好的质量变形码产生相当的性能。为了克服该问题，提出了一种基于基于微灰焦的三角脉冲宽度调制（TPWM）技术产生的相移边缘图案的相位展开方法组合的变形码。使用四步相移方法检索该阶段，并且通过灰度码模式获得相应的相位顺序。由于散焦投影，两个相邻的灰色代码模式的边界变得模糊，这使得恢复准确的灰色码模式困难。为了解决这个问题，我们建议投影全白色模式和全黑色模式以获得阈值，用于执行灰色代码模式的二值化。这种方法是对不同散焦水平的投影仪的鲁棒性。提交实验以验证所提出的技术可用于复杂和/或不连续物体的高精度三维形状测量。

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