There are two kinds of tutorial articles: those that provide a primer on an established topic and those that let us in on the ground floor of something of emerging importance. The first type of tutorial can have a noted expert who has been gracious (and brave) enough to write a field guide about a particular topic. The other sort of tutorial typically involves researchers who have each been laboring on a topic for some years. Both sorts of tutorial articles are very much desired. But we, as an editorial board for both Systems and Transactions, know that there has been no logical place for them in the AESS until this series was started several years ago. With these tutorials, we hope to continue to give them a home, a welcome, and provide a service to our membership. We do not intend to publish tutorials on a regular basis, but we hope to deliver them once or twice per year. We need and welcome good, useful tutorial articles (both kinds) in relevant AESS areas. If you, the reader, can offer a topic of interest and an author to write about it, please contact us. Self-nominations are welcome, and even more ideal is a suggestion of an article that the editor(s) can solicit. All articles will be reviewed in detail. Criteria on which they will be judged include their clarity of presentation, relevance, and likely audience, and, of course, their correctness and scientific merit. As to the mathematical level, the articles in this issue are a good guide: in each case the author has striven to explain complicated topics in simple-well, tutorial-terms. There should be no (or very little) novel material: the home for archival science is the Transactions Magazine, and submissions that need to be properly peer reviewed would be rerouted there. Likewise, articles that are interesting and descriptive, but lack significant tutorial content, ought more properly be submitted to the Systems Magazine.

What is a tutorial

Phase shifting algorithms for fringe projection profilometry: A review

High-speed 3D shape measurement with structured light methods: A review

The previously proposed binary defocusing technique and its variations have proven successful for high-quality three-dimensional (3D) shape measurement when fringe stripes are relatively narrow, but they suffer if fringe stripes are wide. This paper proposes to utilize the binary dithering technique to conquer this challenge. Both simulation and experimental results show the phase error is always less than 0.6% even when the fringe stripes are wide and the projector is nearly focused.

/pdf/three-dimensional-shape-measurement-with-binary-dithered-2yf91hssag.pdf

Three-dimensional shape measurement with binary dithered patterns.

General solution for high dynamic range three-dimensional shape measurement using the fringe projection technique

This paper analyzes the phase error for a three-dimensional (3D) shape measurement system that utilizes our recently proposed projector defocusing technique. This technique generates seemingly sinusoidal structured patterns by defocusing binary structured patterns and then uses these patterns to perform 3D shape measurement by fringe analysis. However, significant errors may still exist if an object is within a certain depth range, where the defocused fringe patterns retain binary structure. In this research, we experimentally studied a large depth range of defocused fringe patterns, from near-binary to near-sinusoidal, and analyzed the associated phase errors. We established a mathematical phase error function in terms of the wrapped phase and the depth z. Finally, we calibrated and used the mathematical function to compensate for the phase error at arbitrary depth ranges within the calibration volume. Experimental results will be presented to demonstrate the success of this proposed technique.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1089&context=me_pubs

Phase error compensation for three-dimensional shape measurement with projector defocusing

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.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1123&context=me_pubs

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

This Letter investigates the effects of different phase-shifting algorithms on the quality of high-resolution three-dimensional (3-D) profilometry produced with nearly focused binary patterns. From theoretical analyses, simulations, and experiments, we found that the nine-step phase-shifting algorithm produces accurate 3-D measurements at high speed without the limited depth range and calibration difficulties that typically plague binary defocusing methods. We also found that the use of more fringe patterns does not necessarily enhance measurement quality.

/pdf/three-dimensional-profilometry-with-nearly-focused-binary-qnn557od4g.pdf

Three-dimensional profilometry with nearly focused binary phase-shifting algorithms

Digital fringe projection (DFP) techniques provide dense 3D measurements of dynamically changing surfaces. Like the human eyes and brain, DFP uses triangulation between matching points in two views of the same scene at different angles to compute depth. However, unlike a stereobased method, DFP uses a digital video projector to replace one of the cameras 1 . The projector rapidly projects a known sinusoidal pattern onto the subject, and the surface of the subject distorts these patterns in the camera’s field of view. Three distorted patterns (fringe images) from the camera can be used to compute the depth using triangulation. Unlike other 3D measurement methods, DFP techniques lead to systems that tend to be faster, lower in equipment cost, more flexible, and easier to develop. DFP systems can also achieve the same measurement resolution as the camera. For this reason, DFP and other digital structured light techniques have recently been the focus of intense research (as summarized in 1-5 ). Taking advantage of DFP, the graphics processing unit, and optimized algorithms, we have developed a system capable of 30 Hz 3D video data acquisition, reconstruction, and display for over 300,000 measurement points per frame 6,7 . Binary defocusing DFP methods can achieve even greater speeds 8 . Diverse applications can benefit from DFP techniques. Our collaborators have used our systems for facial function analysis 9 , facial animation 10 , cardiac mechanics studies 11 , and fluid surface measurements, but many other potential applications exist. This video will teach the fundamentals of DFP techniques and illustrate the design and operation of a binary defocusing DFP system.

/pdf/high-resolution-high-speed-three-dimensional-video-imaging-5fzj341yv7.pdf

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

This study introduces a tool mark analysis approach based upon 3D scans of screwdriver tip and marked plate surfaces at the micrometer scale from an optical microscope. An open-source 3D graphics software package is utilized to simulate the marking process as the projection of the tip's geometry in the direction of tool travel. The edge of this projection becomes a virtual tool mark that is compared to cross-sections of the marked plate geometry using the statistical likelihood algorithm introduced by Chumbley et al. In a study with both sides of six screwdriver tips and 34 corresponding marks, the method distinguished known matches from known nonmatches with zero false-positive matches and two false-negative matches. For matches, it could predict the correct marking angle within ±5–10°. Individual comparisons could be made in seconds on a desktop computer, suggesting that the method could save time for examiners.

Laura Ekstrand

Papers

Phase error compensation for three-dimensional shape measurement with projector defocusing

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

Three-dimensional profilometry with nearly focused binary phase-shifting algorithms

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

Virtual tool mark generation for efficient striation analysis.