3,998 research outputs found
Micro Fourier Transform Profilometry (FTP): 3D shape measurement at 10,000 frames per second
Recent advances in imaging sensors and digital light projection technology
have facilitated a rapid progress in 3D optical sensing, enabling 3D surfaces
of complex-shaped objects to be captured with improved resolution and accuracy.
However, due to the large number of projection patterns required for phase
recovery and disambiguation, the maximum fame rates of current 3D shape
measurement techniques are still limited to the range of hundreds of frames per
second (fps). Here, we demonstrate a new 3D dynamic imaging technique, Micro
Fourier Transform Profilometry (FTP), which can capture 3D surfaces of
transient events at up to 10,000 fps based on our newly developed high-speed
fringe projection system. Compared with existing techniques, FTP has the
prominent advantage of recovering an accurate, unambiguous, and dense 3D point
cloud with only two projected patterns. Furthermore, the phase information is
encoded within a single high-frequency fringe image, thereby allowing
motion-artifact-free reconstruction of transient events with temporal
resolution of 50 microseconds. To show FTP's broad utility, we use it to
reconstruct 3D videos of 4 transient scenes: vibrating cantilevers, rotating
fan blades, bullet fired from a toy gun, and balloon's explosion triggered by a
flying dart, which were previously difficult or even unable to be captured with
conventional approaches.Comment: This manuscript was originally submitted on 30th January 1
Advanced liquid crystal displays with supreme image qualities
Several metrics are commonly used to evaluate the performance of display devices. In this dissertation, we analyze three key parameters: fast response time, wide color gamut, and high contrast ratio, which affect the final perceived image quality. Firstly, we investigate how response time affects the motion blur, and then discover the 2-ms rule. With advanced low-viscosity materials, new operation modes, and backlight modulation technique, liquid crystal displays (LCDs) with an unnoticeable image blur can be realized. Its performance is comparable to an impulse-type display, like cathode ray tube (CRT). Next, we propose two novel backlight configurations to improve an LCD\u27s color gamut. One is to use a functional reflective polarizer (FRP), acting as a notch filter to block the unwanted light, and the other is to combine FRP with a patterned half-wave plate to suppress the crosstalk between blue and green/red lights. In experiment, we achieved 97.3% Rec. 2020 in CIE 1976 color space, which is approaching the color gamut of a laser projector. Finally, to enhance an LCD\u27s contrast ratio, we proposed a novel device configuration by adding an in-cell polarizer between LC layer and color filter array. The CR for a vertically-aligned LCD is improved from 5000:1 to 20,000:1, and the CR for a fringe field switching LCD is improved from 2000:1 to over 3000:1. To further enlarge CR to fulfill the high dynamic range requirement, a dual-panel LCD system is proposed and the measured contrast ratio exceeds 1,000,000:1. Overall speaking, such an innovated LCD exhibits supreme image qualities with motion picture response time comparable to CRT, vivid color to laser projector, and contrast ratio to OLED. Along with other outstanding features, like high peak brightness, high resolution density, long lifetime, and low cost, LCD would continue to maintain its dominance in consumer electronics in the foreseeable future
A Compressive Multi-Mode Superresolution Display
Compressive displays are an emerging technology exploring the co-design of
new optical device configurations and compressive computation. Previously,
research has shown how to improve the dynamic range of displays and facilitate
high-quality light field or glasses-free 3D image synthesis. In this paper, we
introduce a new multi-mode compressive display architecture that supports
switching between 3D and high dynamic range (HDR) modes as well as a new
super-resolution mode. The proposed hardware consists of readily-available
components and is driven by a novel splitting algorithm that computes the pixel
states from a target high-resolution image. In effect, the display pixels
present a compressed representation of the target image that is perceived as a
single, high resolution image.Comment: Technical repor
Temporal phase unwrapping using deep learning
The multi-frequency temporal phase unwrapping (MF-TPU) method, as a classical
phase unwrapping algorithm for fringe projection profilometry (FPP), is capable
of eliminating the phase ambiguities even in the presence of surface
discontinuities or spatially isolated objects. For the simplest and most
efficient case, two sets of 3-step phase-shifting fringe patterns are used: the
high-frequency one is for 3D measurement and the unit-frequency one is for
unwrapping the phase obtained from the high-frequency pattern set. The final
measurement precision or sensitivity is determined by the number of fringes
used within the high-frequency pattern, under the precondition that the phase
can be successfully unwrapped without triggering the fringe order error.
Consequently, in order to guarantee a reasonable unwrapping success rate, the
fringe number (or period number) of the high-frequency fringe patterns is
generally restricted to about 16, resulting in limited measurement accuracy. On
the other hand, using additional intermediate sets of fringe patterns can
unwrap the phase with higher frequency, but at the expense of a prolonged
pattern sequence. Inspired by recent successes of deep learning techniques for
computer vision and computational imaging, in this work, we report that the
deep neural networks can learn to perform TPU after appropriate training, as
called deep-learning based temporal phase unwrapping (DL-TPU), which can
substantially improve the unwrapping reliability compared with MF-TPU even in
the presence of different types of error sources, e.g., intensity noise, low
fringe modulation, and projector nonlinearity. We further experimentally
demonstrate for the first time, to our knowledge, that the high-frequency phase
obtained from 64-period 3-step phase-shifting fringe patterns can be directly
and reliably unwrapped from one unit-frequency phase using DL-TPU
Appearance-based image splitting for HDR display systems
High dynamic range displays that incorporate two optically-coupled image planes have recently been developed. This dual image plane design requires that a given HDR input image be split into two complementary standard dynamic range components that drive the coupled systems, therefore there existing image splitting issue. In this research, two types of HDR display systems (hardcopy and softcopy HDR display) are constructed to facilitate the study of HDR image splitting algorithm for building HDR displays. A new HDR image splitting algorithm which incorporates iCAM06 image appearance model is proposed, seeking to create displayed HDR images that can provide better image quality. The new algorithm has potential to improve image details perception, colorfulness and better gamut utilization. Finally, the performance of the new iCAM06-based HDR image splitting algorithm is evaluated and compared with widely spread luminance square root algorithm through psychophysical studies
High-quality 3D shape measurement with binarized dual phase-shifting method
ABSTRACT
3-D technology is commonplace in today\u27s world. They are used in many dierent aspects
of life. Researchers have been keen on 3-D shape measurement and 3-D reconstruction
techniques in past decades as a result of inspirations from dierent applications ranging from
manufacturing, medicine to entertainment. The techniques can be broadly divided into contact
and non-contact techniques. The contact techniques like coordinate measuring machine
(CMM) dates way back to 1950s. It has been used extensively in the industries since then.
It becomes predominant in industrial inspections owing to its high accuracy in the order of
m. As we know that quality control is an important part of modern industries hence the
technology is enjoying great popularity. However, the main disadvantage of this method is
its slow speeds due to its requirement of point-by-point touch. Also, since this is a contact
process, it might deform a soft object while performing measurements.
Such limitations led the researchers to explore non-contact measurement technologies
(optical metrology techniques). There are a variety of optical techniques developed till now.
Some of the well-known technologies include laser scanners, stereo vision, and structured
light systems. The main limitation of laser scanners is its limited speed due to its point-by-point
or line-by-line scanning process. The stereo vision uses two cameras which take pictures
of the object at two dierent angles. Then epipolar geometry is used to determine the 3-D
coordinates of points in real-world. Such technology imitates human vision, but it had a
few limitations too like the diculty of correspondence detection for uniform or periodic
textures. Hence structured light systems were introduced which addresses the aforementioned
limitations. There are various techniques developed including 2-D pseudo-random codication, binary codication, N-ary codication and digital fringe projection (DFP). The
limitation of 2-D pseudo-random codication technique is its inability to achieve high spatial
resolution since any uniquely generated and projected feature requires a span of several
projector pixels. The binary codication techniques reduce the requirement of 2-D features
to 1-D ones. However, since there are only two intensities, it is dicult to differentiate
between the individual pixels within each black or white stripe. The other disadvantage is
that n patterns are required to encode 2n pixels, meaning that the measurement speeds will
be severely affected if a scene is to be coded with high-resolution. Dierently, DFP uses
continuous sinusoidal patterns. The usage of continuous patterns addresses the main disadvantage
of binary codication (i.e. the inability of this technique to differentiate between
pixels was resolved by using sinusoid patterns). Thus, the spatial resolution is increased up
to camera-pixel-level. On the other hand, since the DFP technique used 8-bit sinusoid patterns,
the speed of measurement is limited to the maximum refreshing rate of 8-bit images
for many video projectors (e.g. 120 Hz). This made it inapplicable for measurements of
highly dynamic scenes. In order to overcome this speed limitation, the binary defocussing
technique was proposed which uses 1-bit patterns to produce sinusoidal prole by projector
defocusing. Although this technique has signicantly boosted the measurement speed up to
kHz-level, if the patterns are not properly defocused (nearly focused or overly defocused),
increased phase noise or harmonic errors will deteriorate the reconstructed surface quality.
In this thesis research, two techniques are proposed to overcome the limitations of both
DFP and binary defocusing technique: binarized dual phase shifting (BDPS) technique and
Hilbert binarized dual phase shifting technique (HBDPS). Both techniques were able to achieve
high-quality 3-D shape measurements even when the projector is not sufficiently defocused.
The harmonic error was reduced by 47% by the BDPS method, and 74% by the HBDPS
method. Moreover, both methods use binary patterns which preserve the speed advantage of the binary technology, hence it is potentially applicable to simultaneous high-speed and
high-accuracy 3D shape measurements
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