Autoexposure for three-dimensional shape measurement using a digital-light-processing projector

Abstract

Automatically adapting the camera exposure time is crucial for industrial applications where minimum human intervention is usually desirable. However, it is very challenging to realize such a capability for a conventional fringe projection system where only a finite increment of the exposure time is allowed due to its digital fringe generation nature. We study the generation of sinusoidal fringe patterns by properly defocusing binary ones, which permits the use of an arbitrary exposure time. This provides the potential to adapt the exposure time automatically. We present the principle of an automatic exposure technique and show some experimental results. Disciplines Computer-Aided Engineering and Design | Graphics and Human Computer Interfaces CommentsThis article is from Optical Engineering 50 (2011) Abstract. Automatically adapting the camera exposure time is crucial for industrial applications where minimum human intervention is usually desirable. However, it is very challenging to realize such a capability for a conventional fringe projection system where only a finite increment of the exposure time is allowed due to its digital fringe generation nature. We study the generation of sinusoidal fringe patterns by properly defocusing binary ones, which permits the use of an arbitrary exposure time. This provides the potential to adapt the exposure time automatically. We present the principle of an automatic exposure technique and show some experimental results. C 2011 Society of Photo-Optical Instrumentation Engineers (SPIE).

Enhanced phase measurement profilometry for industrial 3D inspection automation

“…In particular, the quality of fringe images is the net effect of camera exposure time, camera sensor gain, lens aperture, intensity of projected light, reflectivity and shape of measured surfaces, environment light, shading and occasions, etc., so in order to improve the quality of fringe image of surfaces with large reflectivity variation range, many research works tried to control some of these factors [11][12][13][14][15][16][17][18][19][20]. Kowarschik et al [11] used proper measurement arrangement to avoid saturating camera sensor.…”

“…Waddington et al [14][15][16] proposed an adaptive fringe projection method to resist strong ambient light by controlling the intensity of projected fringe images. Zhang's group proposed a high dynamic range scanning technique [17] and an autoexposure time technique [18] for obtaining a high-quality fringe image. Jiang et al [19] and Zhao et al [20] also proposed a high dynamic range fringe acquisition method to choose the highquality pixels in the fringe images captured at multiple exposure times.…”

“…Many of these methods required to capture large amount of images in 3D measurement, so the measurement speed would slow down. In [18], a proper exposure time can be calibrated based on the analysis of images under pure white illumination before measurement, and the measurement efficiency can be increased. But it did not consider the impact of multiple light paths from the projector to the camera.…”

“…For a given pixel, γ and ρ is constant, and L pa can be approximate to the sum of extra reflections from other patches. The projected light can be regarded as constant over time, for the exposure time is multiple of unit projecting time [18]. Equation (5) becomes…”

High-resolution, High-speed, Three-dimensional Video Imaging with Digital Fringe Projection Techniques

“…Keep in mind that the camera will need to capture the entire set of fringe images for each 3D video frame. High-quality sinusoidal systems require precise synchronization between the projector and the camera; for binary defocusing systems this requirement is more relaxed 20 . 4.…”