1,535 research outputs found
Event-based Vision: A Survey
Event cameras are bio-inspired sensors that differ from conventional frame
cameras: Instead of capturing images at a fixed rate, they asynchronously
measure per-pixel brightness changes, and output a stream of events that encode
the time, location and sign of the brightness changes. Event cameras offer
attractive properties compared to traditional cameras: high temporal resolution
(in the order of microseconds), very high dynamic range (140 dB vs. 60 dB), low
power consumption, and high pixel bandwidth (on the order of kHz) resulting in
reduced motion blur. Hence, event cameras have a large potential for robotics
and computer vision in challenging scenarios for traditional cameras, such as
low-latency, high speed, and high dynamic range. However, novel methods are
required to process the unconventional output of these sensors in order to
unlock their potential. This paper provides a comprehensive overview of the
emerging field of event-based vision, with a focus on the applications and the
algorithms developed to unlock the outstanding properties of event cameras. We
present event cameras from their working principle, the actual sensors that are
available and the tasks that they have been used for, from low-level vision
(feature detection and tracking, optic flow, etc.) to high-level vision
(reconstruction, segmentation, recognition). We also discuss the techniques
developed to process events, including learning-based techniques, as well as
specialized processors for these novel sensors, such as spiking neural
networks. Additionally, we highlight the challenges that remain to be tackled
and the opportunities that lie ahead in the search for a more efficient,
bio-inspired way for machines to perceive and interact with the world
Reflectance Transformation Imaging (RTI) System for Ancient Documentary Artefacts
This tutorial summarises our uses of reflectance transformation imaging in archaeological contexts. It introduces the UK AHRC funded project reflectance Transformation Imaging for Anciant Documentary Artefacts and demonstrates imaging methodologies
Cable-driven parallel robot for transoral laser phonosurgery
Transoral laser phonosurgery (TLP) is a common surgical procedure in otolaryngology.
Currently, two techniques are commonly used: free beam and fibre delivery. For free beam
delivery, in combination with laser scanning techniques, accurate laser pattern scanning can
be achieved. However, a line-of-sight to the target is required. A suspension laryngoscope is
adopted to create a straight working channel for the scanning laser beam, which could
introduce lesions to the patient, and the manipulability and ergonomics are poor. For the fibre
delivery approach, a flexible fibre is used to transmit the laser beam, and the distal tip of the
laser fibre can be manipulated by a flexible robotic tool. The issues related to the limitation
of the line-of-sight can be avoided. However, the laser scanning function is currently lost in
this approach, and the performance is inferior to that of the laser scanning technique in the
free beam approach.
A novel cable-driven parallel robot (CDPR), LaryngoTORS, has been developed for TLP.
By using a curved laryngeal blade, a straight suspension laryngoscope will not be necessary
to use, which is expected to be less traumatic to the patient. Semi-autonomous free path
scanning can be executed, and high precision and high repeatability of the free path can be
achieved. The performance has been verified in various bench and ex vivo tests. The technical
feasibility of the LaryngoTORS robot for TLP was considered and evaluated in this thesis.
The LaryngoTORS robot has demonstrated the potential to offer an acceptable and feasible
solution to be used in real-world clinical applications of TLP.
Furthermore, the LaryngoTORS robot can combine with fibre-based optical biopsy
techniques. Experiments of probe-based confocal laser endomicroscopy (pCLE) and
hyperspectral fibre-optic sensing were performed. The LaryngoTORS robot demonstrates the
potential to be utilised to apply the fibre-based optical biopsy of the larynx.Open Acces
Innovative Techniques for Digitizing and Restoring Deteriorated Historical Documents
Recent large-scale document digitization initiatives have created new modes of access to modern library collections with the development of new hardware and software technologies. Most commonly, these digitization projects focus on accurately scanning bound texts, some reaching an efficiency of more than one million volumes per year. While vast digital collections are changing the way users access texts, current scanning paradigms can not handle many non-standard materials. Documentation forms such as manuscripts, scrolls, codices, deteriorated film, epigraphy, and rock art all hold a wealth of human knowledge in physical forms not accessible by standard book scanning technologies. This great omission motivates the development of new technology, presented by this thesis, that is not-only effective with deteriorated bound works, damaged manuscripts, and disintegrating photonegatives but also easily utilized by non-technical staff. First, a novel point light source calibration technique is presented that can be performed by library staff. Then, a photometric correction technique which uses known illumination and surface properties to remove shading distortions in deteriorated document images can be automatically applied. To complete the restoration process, a geometric correction is applied. Also unique to this work is the development of an image-based uncalibrated document scanner that utilizes the transmissivity of document substrates. This scanner extracts intrinsic document color information from one or both sides of a document. Simultaneously, the document shape is estimated to obtain distortion information. Lastly, this thesis provides a restoration framework for damaged photographic negatives that corrects photometric and geometric distortions. Current restoration techniques for the discussed form of negatives require physical manipulation to the photograph. The novel acquisition and restoration system presented here provides the first known solution to digitize and restore deteriorated photographic negatives without damaging the original negative in any way. This thesis work develops new methods of document scanning and restoration suitable for wide-scale deployment. By creating easy to access technologies, library staff can implement their own scanning initiatives and large-scale scanning projects can expand their current document-sets
Development of a handheld fiber-optic probe-based raman imaging instrumentation: raman chemlighter
Raman systems based on handheld fiber-optic probes offer advantages in terms of smaller sizes and easier access to the measurement sites, which are favorable for biomedical and clinical applications in the complex environment. However, there are several common drawbacks of applying probes for many applications: (1) The fixed working distance requires the user to maintain a certain working distance to acquire higher Raman signals; (2) The single-point-measurement ability restricts realizing a mapping or scanning procedure; (3) Lack of real-time data processing and a straightforward co-registering method to link the Raman information with the respective measurement position. The thesis proposed and experimentally demonstrated various approaches to overcome these drawbacks. A handheld fiber-optic Raman probe with an autofocus unit was presented to overcome the problem arising from using fixed-focus lenses, by using a liquid lens as the objective lens, which allows dynamical adjustment of the focal length of the probe. An implementation of a computer vision-based positional tracking to co-register the regular Raman spectroscopic measurements with the spatial location enables fast recording of a Raman image from a large tissue sample by combining positional tracking of the laser spot through brightfield images. The visualization of the Raman image has been extended to augmented and mixed reality and combined with a 3D reconstruction method and projector-based visualization to offer an intuitive and easily understandable way of presenting the Raman image. All these advances are substantial and highly beneficial to further drive the clinical translation of Raman spectroscopy as potential image-guided instrumentation
Low-cost single-pixel 3D imaging by using an LED array
We propose a method to perform color imaging with a single photodiode by using
light structured illumination generated with a low-cost color LED array. The LED array is
used to generate a sequence of color Hadamard patterns which are projected onto the object
by a simple optical system while the photodiode records the light intensity. A field
programmable gate array (FPGA) controls the LED panel allowing us to obtain high refresh
rates up to 10 kHz. The system is extended to 3D imaging by simply adding a low number of
photodiodes at different locations. The 3D shape of the object is obtained by using a noncalibrated
photometric stereo technique. Experimental results are provided for an LED array
with 32 × 32 elements
A efficient and practical 3D face scanner using near infrared and visible photometric stereo
AbstractThis paper is concerned with the acquisition of model data for automatic 3D face recognition applications. As 3D methods become progressively more popular in face recognition research, the need for fast and accurate data capture has become crucial. This paper is motivated by this need and offers three primary contributions. Firstly, the paper demonstrates that four-source photometric stereo offers a potential means for data capture that is computationally nd financially viable and easily deployable in commercial settings. We have shown that both visible light and less ntrusive near infrared light is suitable for facial illumination. The second contribution is a detailed set of experimental esults that compare the accuracy of the device to ground truth, which was captured using a commercial projected pattern range finder. Importantly, we show that not only is near infrared light a valid alternative to the more commonly xploited visible light, but that it actually gives more accurate reconstructions. Finally, we assess the validity of the Lambertian assumption on skin reflectance data and show that better results may be obtained by incorporating more dvanced reflectance functions, such as the Oren–Nayar model
In-process surface profile assessment of rotary machined timber using a dynamic photometric stereo technique
Machining operations have advanced in speed and there is an increasing demand for higher quality surface finish. It is
therefore necessary to develop real-time surface inspection techniques which will provide sensory information for controlling
the machining processes. This paper describes a practical method for real-time analysis of planed wood using the
photometric stereo technique. Earlier research has shown that the technique is very effective in assessing surface waviness
on static wood samples. In this paper, the photometric stereo method is extended to real industrial applications
where samples are subjected to rapid movements. Surface profiles extracted from the dynamic photometric stereo
method are compared with those from the static measurements and the results show that there is a high correlation
between the two methods
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