22 research outputs found
Enhancing retinal images by nonlinear registration
Being able to image the human retina in high resolution opens a new era in
many important fields, such as pharmacological research for retinal diseases,
researches in human cognition, nervous system, metabolism and blood stream, to
name a few. In this paper, we propose to share the knowledge acquired in the
fields of optics and imaging in solar astrophysics in order to improve the
retinal imaging at very high spatial resolution in the perspective to perform a
medical diagnosis. The main purpose would be to assist health care
practitioners by enhancing retinal images and detect abnormal features. We
apply a nonlinear registration method using local correlation tracking to
increase the field of view and follow structure evolutions using correlation
techniques borrowed from solar astronomy technique expertise. Another purpose
is to define the tracer of movements after analyzing local correlations to
follow the proper motions of an image from one moment to another, such as
changes in optical flows that would be of high interest in a medical diagnosis.Comment: 21 pages, 7 figures, submitted to Optics Communication
Fainter and closer: finding planets by symmetry breaking
Imaging of planets is very difficult, due to the glare from their nearby,
much brighter suns. Static and slowly-evolving aberrations are the limiting
factors, even after application of adaptive optics. The residual speckle
pattern is highly symmetrical due to diffraction from the telescope's aperture.
We suggest to break this symmetry and thus to locate planets hidden beneath it.
An eccentric pupil mask is rotated to modulate the residual light pattern not
removed by other means. This modulation is then exploited to reveal the
planet's constant signal. In well-corrected ground-based observations we can
reach planets six stellar magnitudes fainter than their sun, and only 2-3 times
the diffraction limit from it. At ten times the diffraction limit, we detect
planets 16 magnitudes fainter. The stellar background drops by five magnitudes.Comment: Accepted for publication in Optics Expres
Stellar intensity interferometry: Experimental steps toward long-baseline observations
Experiments are in progress to prepare for intensity interferometry with
arrays of air Cherenkov telescopes. At the Bonneville Seabase site, near Salt
Lake City, a testbed observatory has been set up with two 3-m air Cherenkov
telescopes on a 23-m baseline. Cameras are being constructed, with control
electronics for either off- or online analysis of the data. At the Lund
Observatory (Sweden), in Technion (Israel) and at the University of Utah (USA),
laboratory intensity interferometers simulating stellar observations have been
set up and experiments are in progress, using various analog and digital
correlators, reaching 1.4 ns time resolution, to analyze signals from pairs of
laboratory telescopes.Comment: 12 pages, 3 figur