554,820 research outputs found
Adaptive tone-mapping transfer functions for high dynamic range video cameras
For real-time imaging with digital video cameras, good tonal rendition of video is important to ensure high visual comfort for the user. Except local contrast improvements, high dynamic range (HDR) scenes require adaptive gradation correction (tone-mapping curve) that should enable good visualization of details at lower brightness. We discuss how to construct and control optimal tone mapping curves, which enhance visibility of image details in the dark regions while not excessively compressing the image in the bright image parts. The result of this method is a 21 dB expansion of the dynamic range. The new algorithm was successfully evaluated in HW and is suited for any video system performing HDR video compression
Self-generated Self-similar Traffic
Self-similarity in the network traffic has been studied from several aspects:
both at the user side and at the network side there are many sources of the
long range dependence. Recently some dynamical origins are also identified: the
TCP adaptive congestion avoidance algorithm itself can produce chaotic and long
range dependent throughput behavior, if the loss rate is very high. In this
paper we show that there is a close connection between the static and dynamic
origins of self-similarity: parallel TCPs can generate the self-similarity
themselves, they can introduce heavily fluctuations into the background traffic
and produce high effective loss rate causing a long range dependent TCP flow,
however, the dropped packet ratio is low.Comment: 8 pages, 12 Postscript figures, accepted in Nonlinear Phenomena in
Complex System
Live demonstration: Real-time high dynamic range video acquisition using in-pixel adaptive content-aware tone mapping compression
This demonstration targets the acquisition of realtime video sequences involving High Dynamic Range (HDR) scenes. Adaptation to different illumination conditions while preserving contrast is achieved by using a sensor chip, which implements an adaptive content-aware tone mapping compression algorithm by using in-pixel circuitry. Its response gets adapted to changing illumination conditions by using at each frame a statistical estimation of the light distribution, which is derived from the HDR histogram calculated at the previous frame. This method allows adaptive HDR video, while capable to capture very large DR scenes including moving objects.Office of Naval Research (USA) N000141410355Ministerio de Economía y Competitividad IPT-2011-1625-430000Junta de Andalucía TIC 2338-201
Adaptive Speckle Imaging Interferometry: a new technique for the analysis of microstructure dynamics, drying processes and coating formation
We describe an extension of multi-speckle diffusing wave spectroscopy adapted
to follow the non-stationary microscopic dynamics in drying films and coatings
in a very reactive way and with a high dynamic range. We call this technique
"Adaptive Speckle Imaging Interferometry". We introduce an efficient tool, the
inter-image distance, to evaluate the speckle dynamics, and the concept of
"speckle rate" (SR, in Hz) to quantify this dynamics. The adaptive algorithm
plots a simple kinetics, the time evolution of the SR, providing a non-invasive
characterization of drying phenomena. A new commercial instrument, called
HORUS(R), based on ASII and specialized in the analysis of film formation and
drying processes is presented.Comment: 11 pages, 4 figure
High dynamic range imaging with a single-mode pupil remapping system : a self-calibration algorithm for redundant interferometric arrays
The correction of the influence of phase corrugation in the pupil plane is a
fundamental issue in achieving high dynamic range imaging. In this paper, we
investigate an instrumental setup which consists in applying interferometric
techniques on a single telescope, by filtering and dividing the pupil with an
array of single-mode fibers. We developed a new algorithm, which makes use of
the fact that we have a redundant interferometric array, to completely
disentangle the astronomical object from the atmospheric perturbations (phase
and scintillation). This self-calibrating algorithm can also be applied to any
- diluted or not - redundant interferometric setup. On an 8 meter telescope
observing at a wavelength of 630 nm, our simulations show that a single mode
pupil remapping system could achieve, at a few resolution elements from the
central star, a raw dynamic range up to 10^6; depending on the brightness of
the source. The self calibration algorithm proved to be very efficient,
allowing image reconstruction of faint sources (mag = 15) even though the
signal-to-noise ratio of individual spatial frequencies are of the order of
0.1. We finally note that the instrument could be more sensitive by combining
this setup with an adaptive optics system. The dynamic range would however be
limited by the noise of the small, high frequency, displacements of the
deformable mirror.Comment: 11 pages, 7 figures. Accepted for publication in MNRA
The Structure of High Strehl Ratio Point-Spread Functions
We describe the symmetries present in the point-spread function (PSF) of an
optical system either located in space or corrected by an adaptive o to Strehl
ratios of about 70% and higher. We present a formalism for expanding the PSF to
arbitrary order in terms of powers of the Fourier transform of the residual
phase error, over an arbitrarily shaped and apodized entrance aperture. For
traditional unapodized apertures at high Strehl ratios, bright speckles pinned
to the bright Airy rings are part of an antisymmetric perturbation of the
perfect PSF, arising from the term that is first order in the residual phase
error. There are two symmetric second degree terms. One is negative at the
center, and, like the first order term, is modulated by the perfect image's
field strength -- it reduces to the Marechal approximation at the center of the
PSF. The other is non-negative everywhere, zero at the image center, and can be
responsible for an extended halo -- which limits the dynamic range of faint
companion detection in the darkest portions of the image. In regimes where one
or the other term dominates the speckles in an image, the symmetry of the
dominant term can be exploited to reduce the effect of those speckles,
potentially by an order of magnitude or more. We demonstrate the effects of
both secondary obscuration and pupil apodization on the structure of residual
speckles, and discuss how these symmetries can be exploited by appropriate
telescope and instrument design, observing strategies, and filter bandwidths to
improve the dynamic range of high dynamic range AO and space-based
observations. Finally, we show that our analysis is relevant to high dynamic
range coronagraphy.Comment: Accepted for publication in ApJ; 20 pages, 4 figure
A new technique to reproduced high-dynamic-range images for low-dynamic-range display
Tone mapping is a process for reproduction of High-Dynamic-Range images (HDR) for Low-Dynamic-Range (LDR) output devices. In this report, author presents a new local tone-mapping operator, derived from the Contrast Limited Adaptive histogram Equalization (CLAHE) technique for displaying high dynamic range image. The CLAHE is a method which was originally developed for medical imaging. This method has effectively expanded the full dynamic range of display and it is fully automatic. Due to different luminance intervals could result in overlapped reaction on the limited response in limited response range of visual system, scene region splitting and merging were used to segment the scaled luminance and perform the image segmentation to segment image into smaller part. After the region splitting and merging, there will be some noise or variation of intensity that may result in holes or over segmentation. As the result, the morphological operation, opening and closing were used to perform the mask to applied different clip limit of the CLAHE operation
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