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.

Some recent advances on superfast 3D shape measurement with digital binary defocusing techniques

This paper presents a two-frequency binary phase-shifting technique to measure three-dimensional (3D) absolute shape of beating rabbit hearts. Due to the low contrast of the cardiac surface, the projector and the camera must remain focused, which poses challenges for any existing binary method where the measurement accuracy is low. To conquer this challenge, this paper proposes to utilize the optimal pulse width modulation (OPWM) technique to generate high-frequency fringe patterns, and the error-diffusion dithering technique to produce low-frequency fringe patterns. Furthermore, this paper will show that fringe patterns produced with blue light provide the best quality measurements compared to fringe patterns generated with red or green light; and the minimum data acquisition speed for high quality measurements is around 800 Hz for a rabbit heart beating at 180 beats per minute.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1083&context=me_pubs

3D absolute shape measurement of live rabbit hearts with a superfast two-frequency phase-shifting technique.

Calibration of fringe projection profilometry: A comparative review

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

Our study shows that the phase error caused by improperly defocused binary structured patterns correlates to the depth z. This finding leads to a novel uniaxial three-dimensional shape measurement technique without triangulation. Since the measurement can be performed from the same viewing angle, this proposed method overcomes some limitations of the triangulation-based techniques, such as the problem of measuring deep holes. Our study explains the principle of the technique and presents some experimental results to verify its feasibility.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1071&context=me_conf

Uniaxial three-dimensional shape measurement with projector defocusing

Structured light system calibration has been widely studied over the decades, and a variety of calibration approaches have
been proposed. Among these methods, the flexible method using flat checkerboard is widely adopted. However, there is
a lack of studies on selecting the optimal checker size for high accuracy calibration, whilst it is vital to understanding this
factor. This paper presents a systematic study on how the checker size affects the calibration accuracy for a structured
light system, and provides a general guideline to select the optimal size. For this initial study, 7 different checker sizes are
selected, and experiments demonstrated that the system achieved the best calibration accuracy within a certain range of
checker size.

/pdf/optimal-checkerboard-selection-for-structured-light-system-55o9iub765.pdf

Optimal checkerboard selection for structured light system calibration

Our recent study showed that the phase error caused by improperly defocused binary structured patterns has a unique
relationship with the depth z. Based on this finding, the depth information can be extracted without the need of triangulation.
Because the measurement can be performed from the same viewing angle, this uniaxial measurement technique can
overcome some limitations of a triangulation-based technique, such as measuring a deep hole. This paper will present the
principle of the proposed technique and show some simulation and preliminary experimental results to verify its viability.

Uniaxial 3D shape measurement with projector defocusing

This paper analyzes the phase error for a 3-D shape measurement system that utilizes our recently proposed projector defocusing
technique. In this technique, by defocusing binary structured patterns, seemingly sinusoidal ones can be generated,
and 3-D shape measurement can be performed by fringe analysis. However, there are still significant errors if the object
is not within a certain depth range where the defocused fringe patterns still have binary structures. In this research, we
experimentally studied a large depth range of defocused fringe patterns, from close to be binary to to be sinusoidal, and its
associated phase errors are analyzed. We established a mathematical phase error function in terms of the wrapped phase
and the depth z. Finally, the mathematical function is calibrated and is used to compensate for the phase error at arbitrary
depth ranges within the calibration volume. Experiment will be presented to demonstrate the success of this proposed
technique.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1073&context=me_conf

Ying Xu

Papers

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

Uniaxial three-dimensional shape measurement with projector defocusing

Optimal checkerboard selection for structured light system calibration

Uniaxial 3D shape measurement with projector defocusing

Error analysis for 3D shape measurement with projector defocusing