1,022 research outputs found
Geometry of isophote curves
In this paper, we consider the intensity surface of a 2D image, we study the
evolution of the symmetry sets (and medial axes) of 1-parameter families of
iso-intensity curves. This extends the investigation done on 1-parameter
families of smooth plane curves (Bruce and Giblin, Giblin and Kimia, etc.) to
the general case when the family of curves includes a singular member, as will
happen if the curves are obtained by taking plane sections of a smooth surface,
at the moment when the plane becomes tangent to the surface.
Looking at those surface sections as isophote curves, of the pixel values of
an image embedded in the real plane, this allows us to propose to combine
object representation using a skeleton or symmetry set representation and the
appearance modelling by representing image information as a collection of
medial representations for the level-sets of an image.Comment: 15 pages, 7 figure
Isophote curves on timelike surfaces in Minkowski 3-space
Isophote comprises a locus of the surface points whose normal vectors make a
constant angle with a fixed vector. In this paper, isophote curves are studied
on timelike surfaces in Minkowski 3-space E31. The axises of spacelike and
timelike isophote curves are found via their Darboux frames. Subsequently, the
relationship between isophotes and slant helices is shown on timelike surfaces.Comment: 11 pages. arXiv admin note: text overlap with arXiv:1203.438
Near-infrared observations of galaxies in Pisces-Perseus: I. H-band surface photometry of 174 spirals
We present near-infrared, H-band (1.65 um), surface photometry of 174 spiral
galaxies in the area of the Pisces-Perseus supercluster. The images, acquired
with the ARNICA camera mounted on various telescopes, are used to derive radial
profiles of surface brightness, ellipticities, and position angles, together
with global parameters such as H-band magnitudes and diameters. The mean
relation between H-band isophotal diameter D_{21.5} and the B-band D_{25}
implies a B-H color of the outer disk bluer than 3.5; moreover, D_{21.5}/D_{25}
depends on (global) color and absolute luminosity. The correlations among the
various photometric parameters suggest a ratio between isophotal radius
D_{21.5}/2 and disk scale length of about 3.5 and a mean disk central
brightness of 17.5 H-mag arcsec^{-2}. We confirm the trend of the concentration
index C_{31} with absolute luminosity and, to a lesser degree, with
morphological type. We also assess the influence of non-axisymmetric structures
on the radial profiles and on the derived parameters.Comment: 10 pages, 11 postscript figures (one table and one figure are
available only at the CDS); to be published on A&A
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