41,490 research outputs found
A Retinex-based Image Enhancement Scheme with Noise Aware Shadow-up Function
This paper proposes a novel image contrast enhancement method based on both a
noise aware shadow-up function and Retinex (retina and cortex) decomposition.
Under low light conditions, images taken by digital cameras have low contrast
in dark or bright regions. This is due to a limited dynamic range that imaging
sensors have. For this reason, various contrast enhancement methods have been
proposed. Our proposed method can enhance the contrast of images without not
only over-enhancement but also noise amplification. In the proposed method, an
image is decomposed into illumination layer and reflectance layer based on the
retinex theory, and lightness information of the illumination layer is
adjusted. A shadow-up function is used for preventing over-enhancement. The
proposed mapping function, designed by using a noise aware histogram, allows
not only to enhance contrast of dark region, but also to avoid amplifying
noise, even under strong noise environments.Comment: To appear in IWAIT-IFMIA 201
Single Molecule DNA Detection with an Atomic Vapor Notch Filter
The detection of single molecules has facilitated many advances in life- and
material-sciences. Commonly, it founds on the fluorescence detection of single
molecules, which are for example attached to the structures under study. For
fluorescence microscopy and sensing the crucial parameters are the collection
and detection efficiency, such that photons can be discriminated with low
background from a labeled sample. Here we show a scheme for filtering the
excitation light in the optical detection of single stranded labeled DNA
molecules. We use the narrow-band filtering properties of a hot atomic vapor to
filter the excitation light from the emitted fluorescence of a single emitter.
The choice of atomic sodium allows for the use of fluorescent dyes, which are
common in life-science. This scheme enables efficient photon detection, and a
statistical analysis proves an enhancement of the optical signal of more than
15% in a confocal and in a wide-field configuration.Comment: 9 pages, 5 figure
Optimal control of light propagation through multiple-scattering media in the presence of noise
We study the control of coherent light propagation through
multiple-scattering media in the presence of measurement noise. In our
experiments, we use a two-step optimization procedure to find the optimal
incident wavefront. We conclude that the degree of optimal control of coherent
light propagation through a multiple-scattering medium is only determined by
the number of photoelectrons detected per single speckle spot. The prediction
of our model agrees well with the experimental results. Our results offer
opportunities for imaging applications through scattering media such as
biological tissue in the shot noise limit
Surface-wave-enabled darkfield aperture for background suppression during weak signal detection
Sensitive optical signal detection can often be confounded by the presence of a significant background, and, as such, predetection background suppression is substantively important for weak signal detection. In this paper, we present a novel optical structure design, termed surface-wave-enabled darkfield aperture (SWEDA), which can be directly incorporated onto optical sensors to accomplish predetection background suppression. This SWEDA structure consists of a central hole and a set of groove pattern that channels incident light to the central hole via surface plasmon wave and surface-scattered wave coupling. We show that the surface wave component can mutually cancel the direct transmission component, resulting in near-zero net transmission under uniform normal incidence illumination. Here, we report the implementation of two SWEDA structures. The first structure, circular-groove-based SWEDA, is able to provide polarization-independent suppression of uniform illumination with a suppression factor of 1230. The second structure, linear-groove-based SWEDA, is able to provide a suppression factor of 5080 for transverse-magnetic wave and can serve as a highly compact (5.5 micrometer length) polarization sensor (the measured transmission ratio of two orthogonal polarizations is 6100). Because the exact destructive interference balance is highly delicate and can be easily disrupted by the nonuniformity of the localized light field or light field deviation from normal incidence, the SWEDA can therefore be used to suppress a bright background and allow for sensitive darkfield sensing and imaging (observed image contrast enhancement of 27 dB for the first SWEDA)
Focusing Light through Random Photonic Media by Binary Amplitude Modulation
We study the focusing of light through random photonic materials using
wavefront shaping. We explore a novel approach namely binary amplitude
modulation. To this end, the light incident to a random photonic medium is
spatially divided into a number of segments. We identify the segments that give
rise to fields that are out of phase with the total field at the intended focus
and assign these a zero amplitude, whereas the remaining segments maintain
their original amplitude. Using 812 independently controlled segments of light,
we find the intensity at the target to be 75 +/- 6 times enhanced over the
average intensity behind the sample. We experimentally demonstrate focusing of
light through random photonic media using both an amplitude only mode liquid
crystal spatial light modulator and a MEMS-based spatial light modulator. Our
use of Micro Electro-Mechanical System (MEMS)-based digital micromirror devices
for the control of the incident light field opens an avenue to high speed
implementations of wavefront shaping
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