6,256 research outputs found
On The Continuous Steering of the Scale of Tight Wavelet Frames
In analogy with steerable wavelets, we present a general construction of
adaptable tight wavelet frames, with an emphasis on scaling operations. In
particular, the derived wavelets can be "dilated" by a procedure comparable to
the operation of steering steerable wavelets. The fundamental aspects of the
construction are the same: an admissible collection of Fourier multipliers is
used to extend a tight wavelet frame, and the "scale" of the wavelets is
adapted by scaling the multipliers. As an application, the proposed wavelets
can be used to improve the frequency localization. Importantly, the localized
frequency bands specified by this construction can be scaled efficiently using
matrix multiplication
Blind Curvelet based Denoising of Seismic Surveys in Coherent and Incoherent Noise Environments
The localized nature of curvelet functions, together with their frequency and
dip characteristics, makes the curvelet transform an excellent choice for
processing seismic data. In this work, a denoising method is proposed based on
a combination of the curvelet transform and a whitening filter along with
procedure for noise variance estimation. The whitening filter is added to get
the best performance of the curvelet transform under coherent and incoherent
correlated noise cases, and furthermore, it simplifies the noise estimation
method and makes it easy to use the standard threshold methodology without
digging into the curvelet domain. The proposed method is tested on
pseudo-synthetic data by adding noise to real noise-less data set of the
Netherlands offshore F3 block and on the field data set from east Texas, USA,
containing ground roll noise. Our experimental results show that the proposed
algorithm can achieve the best results under all types of noises (incoherent or
uncorrelated or random, and coherent noise)
Dual channel rank-based intensity weighting for quantitative co-localization of microscopy images
BACKGROUND: Accurate quantitative co-localization is a key parameter in the context of understanding the spatial co-ordination of molecules and therefore their function in cells. Existing co-localization algorithms consider either the presence of co-occurring pixels or correlations of intensity in regions of interest. Depending on the image source, and the algorithm selected, the co-localization coefficients determined can be highly variable, and often inaccurate. Furthermore, this choice of whether co-occurrence or correlation is the best approach for quantifying co-localization remains controversial. RESULTS: We have developed a novel algorithm to quantify co-localization that improves on and addresses the major shortcomings of existing co-localization measures. This algorithm uses a non-parametric ranking of pixel intensities in each channel, and the difference in ranks of co-localizing pixel positions in the two channels is used to weight the coefficient. This weighting is applied to co-occurring pixels thereby efficiently combining both co-occurrence and correlation. Tests with synthetic data sets show that the algorithm is sensitive to both co-occurrence and correlation at varying levels of intensity. Analysis of biological data sets demonstrate that this new algorithm offers high sensitivity, and that it is capable of detecting subtle changes in co-localization, exemplified by studies on a well characterized cargo protein that moves through the secretory pathway of cells. CONCLUSIONS: This algorithm provides a novel way to efficiently combine co-occurrence and correlation components in biological images, thereby generating an accurate measure of co-localization. This approach of rank weighting of intensities also eliminates the need for manual thresholding of the image, which is often a cause of error in co-localization quantification. We envisage that this tool will facilitate the quantitative analysis of a wide range of biological data sets, including high resolution confocal images, live cell time-lapse recordings, and high-throughput screening data sets
Properties of Umbral Dots from Stray Light Corrected Hinode Filtergrams
High resolution blue continuum filtergrams from Hinode are employed to study
the umbral fine structure of a regular unipolar sunspot. The removal of
scattered light from the images increases the rms contrast by a factor of 1.45
on average. Improvement in image contrast renders identification of short
filamentary structures resembling penumbrae that are well separated from the
umbra-penumbra boundary and comprise bright filaments/grains flanking dark
filaments. Such fine structures were recently detected from ground based
telescopes and have now been observed with Hinode. A multi-level tracking
algorithm was used to identify umbral dots in both the uncorrected and
corrected images and to track them in time. The distribution of the values
describing the photometric and geometric properties of umbral dots are more
easily affected by the presence of stray light while it is less severe in the
case of kinematic properties. Statistically, umbral dots exhibit a peak
intensity, effective diameter, lifetime, horizontal speed and a trajectory
length of 0.29 I_QS, 272 km, 8.4 min, 0.45 km/s and 221 km respectively. The 2
hr 20 min time sequence depicts several locations where umbral dots tend to
appear and disappear repeatedly with various time intervals. The correction for
scattered light in the Hinode filtergrams facilitates photometry of umbral fine
structure which can be related to results obtained from larger telescopes and
numerical simulations.Comment: Accepted for publication in ApJ : 10 pages, 10 figures, 3 table
A hybrid approach to segmentation of medical images
The paper presents information theory based image segmentation algorithms. Both advantages and problems related to them are discussed. Then a segmentation framework based on combination of information theory and fuzzy logic is proposed
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