24,304 research outputs found
Fast artifacts-free image interpolation
In this paper we describe a novel general purpose image interpolation method based on the combination of two different procedures. First, an adaptive algorithm is applied interpolating locally pixel values along the direction where second order image derivative is lower. Then interpolated values are modified using an iterative refinement minimizing differences in second order image derivatives, maximizing second order derivative values and smoothing isolevel curves. The first algorithm itself provides edge preserving images that are measurably better than those obtained with similarly fast methods presented in the literature. The full method provides interpolated images with a ”natural ” appearance that do not present the artifacts affecting linear and nonlinear methods. Objective and subjective tests on a wide series of natural images clearly show the advantages of the proposed technique over existing approaches.
Image interpolation using Shearlet based iterative refinement
This paper proposes an image interpolation algorithm exploiting sparse
representation for natural images. It involves three main steps: (a) obtaining
an initial estimate of the high resolution image using linear methods like FIR
filtering, (b) promoting sparsity in a selected dictionary through iterative
thresholding, and (c) extracting high frequency information from the
approximation to refine the initial estimate. For the sparse modeling, a
shearlet dictionary is chosen to yield a multiscale directional representation.
The proposed algorithm is compared to several state-of-the-art methods to
assess its objective as well as subjective performance. Compared to the cubic
spline interpolation method, an average PSNR gain of around 0.8 dB is observed
over a dataset of 200 images
Detection and Removal of Artifacts in Astronomical Images
Astronomical images from optical photometric surveys are typically
contaminated with transient artifacts such as cosmic rays, satellite trails and
scattered light. We have developed and tested an algorithm that removes these
artifacts using a deep, artifact free, static sky coadd image built up through
the median combination of point spread function (PSF) homogenized, overlapping
single epoch images. Transient artifacts are detected and masked in each single
epoch image through comparison with an artifact free, PSF-matched simulated
image that is constructed using the PSF-corrected, model fitting catalog from
the artifact free coadd image together with the position variable PSF model of
the single epoch image. This approach works well not only for cleaning single
epoch images with worse seeing than the PSF homogenized coadd, but also the
traditionally much more challenging problem of cleaning single epoch images
with better seeing. In addition to masking transient artifacts, we have
developed an interpolation approach that uses the local PSF and performs well
in removing artifacts whose widths are smaller than the PSF full width at half
maximum, including cosmic rays, the peaks of saturated stars and bleed trails.
We have tested this algorithm on Dark Energy Survey Science Verification data
and present performance metrics. More generally, our algorithm can be applied
to any survey which images the same part of the sky multiple times.Comment: 17 pages, 6 figures. Accepted for publication in Astronomy and
Computin
Aggregated motion estimation for real-time MRI reconstruction
Real-time magnetic resonance imaging (MRI) methods generally shorten the
measuring time by acquiring less data than needed according to the sampling
theorem. In order to obtain a proper image from such undersampled data, the
reconstruction is commonly defined as the solution of an inverse problem, which
is regularized by a priori assumptions about the object. While practical
realizations have hitherto been surprisingly successful, strong assumptions
about the continuity of image features may affect the temporal fidelity of the
estimated images. Here we propose a novel approach for the reconstruction of
serial real-time MRI data which integrates the deformations between nearby
frames into the data consistency term. The method is not required to be affine
or rigid and does not need additional measurements. Moreover, it handles
multi-channel MRI data by simultaneously determining the image and its coil
sensitivity profiles in a nonlinear formulation which also adapts to
non-Cartesian (e.g., radial) sampling schemes. Experimental results of a motion
phantom with controlled speed and in vivo measurements of rapid tongue
movements demonstrate image improvements in preserving temporal fidelity and
removing residual artifacts.Comment: This is a preliminary technical report. A polished version is
published by Magnetic Resonance in Medicine. Magnetic Resonance in Medicine
201
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