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many sources of unquestionable interest, like galaxies, appear in a variety of shapes and scales
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many sources of unquestionable interest, like galaxies, appear in a variety of shapes and scales
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on astronomical \index{image} images.
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on astronomical \index{image} images.
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A perfectly optimized detection routine should ultimately apply all relevant
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A perfectly optimized detection routine should ultimately apply all relevant
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\index{convolution} convolution kernels one after the other in order to make a complete catalogue. Approximations
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\index{convolution} convolution kernels one after the other in order to make a complete catalogue. Approximations
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to this approach are the (isotropic) \index{wavelet} wavelet analysis mentioned earlier, or the more empirical
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to this approach are the (isotropic) \index{wavelet} wavelet analysis mentioned earlier, or the more empirical
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\index{ImCat} ImCat algorithm (Kaiser \etal 1995), for both of which sources to detect are assumed to be
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\index{ImCat} ImCat algorithm (Kaiser \etal 1995), both of which assume that
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the sources are
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reasonably round. The impact on \index{memory} memory usage and processing speed of such refinements is currently
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reasonably round. The impact on \index{memory} memory usage and processing speed of such refinements is currently
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judged too severe to be applied in {\sc SExtractor}. Simple filtering does a good job in general:
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judged too severe to be applied in {\sc SExtractor}. Simple filtering does a good job in general:
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the topological constraints added by the \index{segmentation} segmentation process make the detection somewhat tolerant
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the topological constraints added by the \index{segmentation} segmentation process make the detection somewhat tolerant
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towards larger objects. Extended, very Low-Surface-Brightness (LSB) features found in astronomical
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towards larger objects. Extended, very Low-Surface-Brightness (LSB) features found in astronomical
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\index{image} images are often artifacts (flat-fielding errors, optical ``ghosts'' or halos). However, it is
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\index{image} images are often artifacts (flat-fielding errors, optical ``ghosts'' or halos). However, it is
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