Three-dimensional shape measurement of complex surfaces based on optimized dithering fringe patterns

Abstract

Background: Optimized dithering fringe pattern is a promising method for high-speed, high-accuracy threedimensional 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. Methods: In 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 discussion: Both 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. Conclusions: The 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.

Measurement of step surface contour based on variable sampling phase shift interference phase extraction algorithm based on selective sampling

“…From the early phase-shift algorithm including the Hariharan algorithm and the Schwider algorithm to the current frequency-conversion phase-shift algorithm including the iterative algorithm and the principal element analysis method, we can come to a conclusion that the research of the frequency conversion phase shift algorithm has become the trend of modern phase-shift interferometry research [1]. Although the principal element analysis (PCA) and Advanced iterative algorithm (AIA) can be used to recover the phase information from a large number of phase-shifted interferogram efficiently [2][3][4][5], a series of error sources and the complexity of measured surface do exist in the actual measuring process [6,7]. And the traditional phase-shift interference algorithm exposes some drawbacks, such as the effect of noise and phase shift error on phase extraction precision of stochastic phase-shift algorithm [8], the influence of the background intensity and modulation system on phase-shift algorithm, and slow rate of operation as well as low precision of the result [3,9,10].…”

“…In order to solve the above drawbacks, Yang Mu, Hou Lizhou and others proposed a stochastic phase-shifted phase solution method based on least squares iteration, whereas running computing time will be increased obviously and phase extraction accuracy will mostly be lowered when interference fringe graphs with lots of pixels are available to be dealt with in the iterative operation period [3,11,12]. In this paper, the iterative algorithm is used to solve the phase, and it is improved and deeply researched, and a high efficient and accurate phase extraction algorithm is proposed, which differs from the traditional method in the study of phase extraction with random sampling to simplify operation and improve accuracy [13][14][15][16].…”