Abstract
BackgroundOptimized dithering fringe pattern is a promising method for high-speed, high-accuracy three-dimensional shape measurement. The recently proposed dithering optimization technology optimizes the fringe quality in either phase domain or intensity domain according to their objective functions. Phase-based optimization is direct and effective, but it is sensitive to projector defocusing levels. Intensity-based optimization is robust to projector defocusing levels, but it does not fully improve the phase quality. In practice, it is difficult to control defocusing levels so it is still a challenge to get high quality fringe patterns which affects the measurement quality under different defocusing levels.MethodsIn order to get high-quality binary dithered patterns which are robust to defocusing levels, this paper proposes a weight object function. This function combines two parts: a global intensity part and a local structure part. The global intensity measurement is based on the normalized mean squared error. The local structure measurement is based on residual error of intensity. To generate high quality fringe patterns, the weight object function is applied to the best patch framework.Results and discussionBoth simulation and experimental results demonstrate that the phase-based optimization method and the proposed method perform better than the intensity-based optimization method under nearly focused. However the quality of measurement results from phase-based optimization will decrease with the defoucsing levels increasing. The proposed method is robust to the defocusing levels and it can still reduce the phase error when the projector is strongly defocused.ConclusionsThe proposed method can get high-quality binary dithered patterns under different defocusing levels by combining global similarity and local residual error of intensity. It inherits the merits of binary fringe pattern so that gamma calibration of projector is not required. In practice, the proposed method can be used to generate high quality fringe patterns. The experiment results verify that the proposed method can get better measurement results without considering the projector defocusing levels.
Highlights
In the past decades, digital fringe projection (DFP) methods have been proposed as one of the most reliable techniques to reconstruct the surface of objects because of their accuracy and efficiency [1,2,3]
Binary defocusing technique cannot achieve the same measurement capability compared with conventional DFP methods: (1) the measurement accuracy decreases due to high-frequency harmonics influence and (2) the measurement range is smaller since the projector must be properly focused for high-quality measurement [13,14,15]
Improvement is limited to wide fringe stripes, because the modulation is only one-dimensional without making full use of two-dimensional information
Summary
Digital fringe projection (DFP) methods have been proposed as one of the most reliable techniques to reconstruct the surface of objects because of their accuracy and efficiency [1,2,3]. Conventional DFP technique has major limitations: the projection nonlinearity and speed bottleneck [6,7,8,9]. These shortcomings make it difficult to be applied to high-quality and high-speed 3D shape measurement. Binary defocusing technique cannot achieve the same measurement capability compared with conventional DFP methods: (1) the measurement accuracy decreases due to high-frequency harmonics influence and (2) the measurement range is smaller since the projector must be properly focused for high-quality measurement [13,14,15]. Optimized dithering fringe pattern is a promising method for high-speed, high-accuracy threedimensional shape measurement. It is difficult to control defocusing levels so it is still a challenge to get high quality fringe patterns which affects the measurement quality under different defocusing levels
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