Automated High-Dynamic-Range Three-Dimensional Optical Metrology Technique

Abstract

Measuring three-dimensional (3D) surfaces with extremely high contrast (e.g., partially shiny surfaces) is extremely difficult with optical metrology methods. Conventional techniques, which involve measurement from multiple angles or camera aperture adjustments, pose issues for high accuracy measurement in the manufacturing industry because they are difficult to automate and often induce undesirable vibrations in the calibrated measurement system. This paper presents a framework for optically capturing high-contrast 3D surfaces via flexible exposure time variation. This technique leverages the binary defocusing technique that was recently developed at Iowa State University to allow digital fringe projection with a camera exposure time far shorter than the projector’s projection period. Since the camera exposure time can be rapidly adjusted in software, the proposed technique could be automated without mechanical adjustments to the measurement system. Moreover, the exposure times are sufficiently short as to be efficiently packed into a projection period, giving this technique the potential for high speed applications. Experimental results will be presented to demonstrate the success of the proposed method.

High Dynamic Range Saturation Intelligence Avoidance for Three-Dimensional Shape Measurement

“…Moreover, to determine the value of the parameter according to the specific color distribution of object surface is difficult. For the more, an auto exposure technique and an automated high-dynamic-range 3D optical metrology was bring up in [12], which could predict the required exposure time adaptively. They both use the binary defocusing technology and thus could adjust the exposure time casually without the restraint of the projector's refresh frequency.…”

Real-time high-dynamic-range fringe acquisition for 3D shape measurement with a RGB camera

“…To address the aforementioned limitations of conventional high-contrast surface measurements, researchers have started to seek novel solutions by developing HDR in 3D shape measurement. The mainstream of HDR approaches can be divided into techniques based on camera exposure control [11][12][13][14][15][16] and projector fringe pattern modulation [17][18][19][20][21][22][23][24]. The technologies based on camera exposure control essentially acquire fringe images with different camera exposure times, and then achieve HDR effect in 3D shape measurements either by fusion of the fringe images with varying exposures [11,12] or by identifying the optimal exposure time via post-fringe analysis [13][14][15][16].…”

High dynamic range real-time 3D shape measurement

“…HDR 3D shape measurement techniques can be classified into two categories: 1) using multiple exposures without pre-analysis [1,2]; and 2) finding optimal exposures through preanalysis [3][4][5][6]. All aforementioned HDR methods coincidently took advantage of pixel-bypixel measurement of fringe analysis methods.…”