31,315 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
Computational temporal ghost imaging
Ghost imaging is a fascinating process, where light interacting with an
object is recorded without resolution, but the shape of the object is
nevertheless retrieved, thanks to quantum or classical correlations of this
interacting light with either a computed or detected random signal. Recently,
ghost imaging has been extended to a time object, by using several thousands
copies of this periodic object. Here, we present a very simple device, inspired
by computational ghost imaging, that allows the retrieval of a single
non-reproducible, periodic or non-periodic, temporal signal. The reconstruction
is performed by a single shot, spatially multiplexed, measurement of the
spatial intensity correlations between computer-generated random images and the
images, modulated by a temporal signal, recorded and summed on a chip CMOS
camera used with no temporal resolution. Our device allows the reconstruction
of either a single temporal signal with monochrome images or
wavelength-multiplexed signals with color images
Encoding of arbitrary micrometric complex illumination patterns with reduced speckle
In nonlinear microscopy, phase-only spatial light modulators (SLMs) allow
achieving simultaneous two-photon excitation and fluorescence emission from specific regionof-interests (ROIs). However, as iterative Fourier transform algorithms (IFTAs) can only
approximate the illumination of selected ROIs, both image formation and/or signal acquisition
can be largely affected by the spatial irregularities of the illumination patterns and the speckle
noise. To overcome these limitations, we propose an alternative complex illumination method
(CIM) able to generate simultaneous excitation of large-area ROIs with full control over the
amplitude and phase of light and reduced speckle. As a proof-of-concept we experimentally
demonstrate single-photon and second harmonic generation (SHG) with structured
illumination over large-area ROIs
Mitigation of H.264 and H.265 Video Compression for Reliable PRNU Estimation
The photo-response non-uniformity (PRNU) is a distinctive image sensor
characteristic, and an imaging device inadvertently introduces its sensor's
PRNU into all media it captures. Therefore, the PRNU can be regarded as a
camera fingerprint and used for source attribution. The imaging pipeline in a
camera, however, involves various processing steps that are detrimental to PRNU
estimation. In the context of photographic images, these challenges are
successfully addressed and the method for estimating a sensor's PRNU pattern is
well established. However, various additional challenges related to generation
of videos remain largely untackled. With this perspective, this work introduces
methods to mitigate disruptive effects of widely deployed H.264 and H.265 video
compression standards on PRNU estimation. Our approach involves an intervention
in the decoding process to eliminate a filtering procedure applied at the
decoder to reduce blockiness. It also utilizes decoding parameters to develop a
weighting scheme and adjust the contribution of video frames at the macroblock
level to PRNU estimation process. Results obtained on videos captured by 28
cameras show that our approach increases the PRNU matching metric up to more
than five times over the conventional estimation method tailored for photos
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