38 research outputs found
Real-time refocusing using an FPGA-based standard plenoptic camera
Plenoptic cameras are receiving increased attention in scientific and commercial applications because they capture the entire structure of light in a scene, enabling optical transforms (such as focusing) to be applied computationally after the fact, rather than once and for all at the time a picture is taken. In many settings, real-time inter active performance is also desired, which in turn requires significant computational power due to the large amount of data required to represent a plenoptic image. Although GPUs have been shown to provide acceptable performance for real-time plenoptic rendering, their cost and power requirements make them prohibitive for embedded uses (such as in-camera). On the other hand, the computation to accomplish plenoptic rendering is well structured, suggesting the use of specialized hardware. Accordingly, this paper presents an array of switch-driven finite impulse response filters, implemented with FPGA to accomplish high-throughput spatial-domain rendering. The proposed architecture provides a power-efficient rendering hardware design suitable for full-video applications as required in broadcasting or cinematography. A benchmark assessment of the proposed hardware implementation shows that real-time performance can readily be achieved, with a one order of magnitude performance improvement over a GPU implementation and three orders ofmagnitude performance improvement over a general-purpose CPU implementation
Exploring plenoptic properties of correlation imaging with chaotic light
In a setup illuminated by chaotic light, we consider different schemes that
enable to perform imaging by measuring second-order intensity correlations. The
most relevant feature of the proposed protocols is the ability to perform
plenoptic imaging, namely to reconstruct the geometrical path of light
propagating in the system, by imaging both the object and the focusing element.
This property allows to encode, in a single data acquisition, both
multi-perspective images of the scene and light distribution in different
planes between the scene and the focusing element. We unveil the plenoptic
property of three different setups, explore their refocusing potentialities and
discuss their practical applications.Comment: 9 pages, 4 figure
Correlation Plenoptic Imaging With Entangled Photons
Plenoptic imaging is a novel optical technique for three-dimensional imaging
in a single shot. It is enabled by the simultaneous measurement of both the
location and the propagation direction of light in a given scene. In the
standard approach, the maximum spatial and angular resolutions are inversely
proportional, and so are the resolution and the maximum achievable depth of
focus of the 3D image. We have recently proposed a method to overcome such
fundamental limits by combining plenoptic imaging with an intriguing
correlation remote-imaging technique: ghost imaging. Here, we theoretically
demonstrate that correlation plenoptic imaging can be effectively achieved by
exploiting the position-momentum entanglement characterizing spontaneous
parametric down-conversion (SPDC) photon pairs. As a proof-of-principle
demonstration, we shall show that correlation plenoptic imaging with entangled
photons may enable the refocusing of an out-of-focus image at the same depth of
focus of a standard plenoptic device, but without sacrificing
diffraction-limited image resolution.Comment: 12 pages, 5 figure
Towards quantum 3d imaging devices
We review the advancement of the research toward the design and implementation of quantum plenoptic cameras, radically novel 3D imaging devices that exploit both momentum–position entanglement and photon–number correlations to provide the typical refocusing and ultra-fast, scanning-free, 3D imaging capability of plenoptic devices, along with dramatically enhanced performances, unattainable in standard plenoptic cameras: diffraction-limited resolution, large depth of focus, and ultra-low noise. To further increase the volumetric resolution beyond the Rayleigh diffraction limit, and achieve the quantum limit, we are also developing dedicated protocols based on quantum Fisher information. However, for the quantum advantages of the proposed devices to be effective and appealing to end-users, two main challenges need to be tackled. First, due to the large number of frames required for correlation measurements to provide an acceptable signal-to-noise ratio, quantum plenoptic imaging (QPI) would require, if implemented with commercially available high-resolution cameras, acquisition times ranging from tens of seconds to a few minutes. Second, the elaboration of this large amount of data, in order to retrieve 3D images or refocusing 2D images, requires high-performance and time-consuming computation. To address these challenges, we are developing high-resolution single-photon avalanche photodiode (SPAD) arrays and high-performance low-level programming of ultra-fast electronics, combined with compressive sensing and quantum tomography algorithms, with the aim to reduce both the acquisition and the elaboration time by two orders of magnitude. Routes toward exploitation of the QPI devices will also be discussed
Implementation of a Depth from Light Field Algorithm on FPGA
A light field is a four-dimensional function that grabs the intensity of light rays traversing an empty space at each point. The light field can be captured using devices designed specifically for this purpose and it allows one to extract depth information about the scene. Most light-field algorithms require a huge amount of processing power. Fortunately, in recent years, parallel hardware has evolved and enables such volumes of data to be processed. Field programmable gate arrays are one such option. In this paper, we propose two hardware designs that share a common construction block to compute a disparity map from light-field data. The first design employs serial data input into the hardware, while the second employs view parallel input. These designs focus on performing calculations during data read-in and producing results only a few clock cycles after read-in. Several experiments were conducted. First, the influence of using fixed-point arithmetic on accuracy was tested using synthetic light-field data. Also tests on actual light field data were performed. The performance was compared to that of a CPU, as well as an embedded processor. Our designs showed similar performance to the former and outperformed the latter. For further comparison, we also discuss the performance difference between our designs and other designs described in the literatur
Correlation Plenoptic Imaging between Arbitrary Planes
We propose a novel method to perform plenoptic imaging at the diffraction
limit by measuring second-order correlations of light between two reference
planes, arbitrarily chosen, within the tridimensional scene of interest. We
show that for both chaotic light and entangled-photon illumination, the
protocol enables to change the focused planes, in post-processing, and to
achieve an unprecedented combination of image resolution and depth of field. In
particular, the depth of field results larger by a factor 3 with respect to
previous correlation plenoptic imaging protocols, and by an order of magnitude
with respect to standard imaging, while the resolution is kept at the
diffraction limit. The results lead the way towards the development of compact
designs for correlation plenoptic imaging devices based on chaotic light, as
well as high-SNR plenoptic imaging devices based on entangled photon
illumination, thus contributing to make correlation plenoptic imaging
effectively competitive with commercial plenoptic devices.Comment: 12 pages, 6 figure
Correlated-photon imaging at 10 volumetric images per second
The correlation properties of light provide an outstanding tool to overcome
the limitations of traditional imaging techniques. A relevant case is
represented by correlation plenoptic imaging (CPI), a quantum-inspired
volumetric imaging protocol employing spatio-temporally correlated photons from
either entangled or chaotic sources to address the main limitations of
conventional light-field imaging, namely, the poor spatial resolution and the
reduced change of perspective for 3D imaging. However, the application
potential of high-resolution imaging modalities relying on photon correlations
is limited, in practice, by the need to collect a large number of frames. This
creates a gap, unacceptable for many relevant tasks, between the time
performance of correlated-light imaging and that of traditional imaging
methods. In this article, we address this issue by exploiting the photon number
correlations intrinsic in chaotic light, combined with a cutting-edge ultrafast
sensor made of a large array of single-photon avalanche diodes (SPADs). This
combination of source and sensor is embedded within a novel single-lens CPI
scheme enabling to acquire 10 volumetric images per second. Our results place
correlated-photon imaging at a competitive edge and prove its potential in
practical applications.Comment: 13 pages, 6 figure
The standard plenoptic camera: applications of a geometrical light field model
A thesis submitted to the University of Bedfordshire, in partial fulfilment of the requirements for the degree of Doctor of PhilosophyThe plenoptic camera is an emerging technology in computer vision able to capture
a light field image from a single exposure which allows a computational change of
the perspective view just as the optical focus, known as refocusing. Until now there was
no general method to pinpoint object planes that have been brought to focus or stereo
baselines of perspective views posed by a plenoptic camera.
Previous research has presented simplified ray models to prove the concept of refocusing
and to enhance image and depth map qualities, but lacked promising distance
estimates and an efficient refocusing hardware implementation. In this thesis, a pair of
light rays is treated as a system of linear functions whose solution yields ray intersections
indicating distances to refocused object planes or positions of virtual cameras that project
perspective views. A refocusing image synthesis is derived from the proposed ray model
and further developed to an array of switch-controlled semi-systolic FIR convolution
filters. Their real-time performance is verified through simulation and implementation by
means of an FPGA using VHDL programming.
A series of experiments is carried out with different lenses and focus settings, where
prediction results are compared with those of a real ray simulation tool and processed
light field photographs for which a blur metric has been considered. Predictions accurately
match measurements in light field photographs and signify deviations of less than 0.35 %
in real ray simulation. A benchmark assessment of the proposed refocusing hardware
implementation suggests a computation time speed-up of 99.91 % in comparison with a
state-of-the-art technique.
It is expected that this research supports in the prototyping stage of plenoptic cameras
and microscopes as it helps specifying depth sampling planes, thus localising objects and
provides a power-efficient refocusing hardware design for full-video applications as in
broadcasting or motion picture arts
Sensors and Technologies in Spain: State-of-the-Art
The aim of this special issue was to provide a comprehensive view on the state-of-the-art sensor technology in Spain. Different problems cause the appearance and development of new sensor technologies and vice versa, the emergence of new sensors facilitates the solution of existing real problems. [...