16,412 research outputs found
Image segmentation with adaptive region growing based on a polynomial surface model
A new method for segmenting intensity images into smooth surface segments is presented. The main idea is to divide the image into flat, planar, convex, concave, and saddle patches that coincide as well as possible with meaningful object features in the image. Therefore, we propose an adaptive region growing algorithm based on low-degree polynomial fitting. The algorithm uses a new adaptive thresholding technique with the L∞ fitting cost as a segmentation criterion. The polynomial degree and the fitting error are automatically adapted during the region growing process. The main contribution is that the algorithm detects outliers and edges, distinguishes between strong and smooth intensity transitions and finds surface segments that are bent in a certain way. As a result, the surface segments corresponding to meaningful object features and the contours separating the surface segments coincide with real-image object edges. Moreover, the curvature-based surface shape information facilitates many tasks in image analysis, such as object recognition performed on the polynomial representation. The polynomial representation provides good image approximation while preserving all the necessary details of the objects in the reconstructed images. The method outperforms existing techniques when segmenting images of objects with diffuse reflecting surfaces
Dose, exposure time, and resolution in Serial X-ray Crystallography
The resolution of X-ray diffraction microscopy is limited by the maximum dose
that can be delivered prior to sample damage. In the proposed Serial
Crystallography method, the damage problem is addressed by distributing the
total dose over many identical hydrated macromolecules running continuously in
a single-file train across a continuous X-ray beam, and resolution is then
limited only by the available molecular and X-ray fluxes and molecular
alignment. Orientation of the diffracting molecules is achieved by laser
alignment. We evaluate the incident X-ray fluence (energy/area) required to
obtain a given resolution from (1) an analytical model, giving the count rate
at the maximum scattering angle for a model protein, (2) explicit simulation of
diffraction patterns for a GroEL-GroES protein complex, and (3) the frequency
cut off of the transfer function following iterative solution of the phase
problem, and reconstruction of an electron density map in the projection
approximation. These calculations include counting shot noise and multiple
starts of the phasing algorithm. The results indicate counting time and the
number of proteins needed within the beam at any instant for a given resolution
and X-ray flux. We confirm an inverse fourth power dependence of exposure time
on resolution, with important implications for all coherent X-ray imaging. We
find that multiple single-file protein beams will be needed for sub-nanometer
resolution on current third generation synchrotrons, but not on fourth
generation designs, where reconstruction of secondary protein structure at a
resolution of 0.7 nm should be possible with short exposures.Comment: 19 pages, 7 figures, 1 tabl
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