# public documents.sextractor_doc

## [/] [whatis.tex] - Rev 19

\chapter{What is {\sc SExtractor}?}
{\sc SExtractor} ({\em Source-Extractor}) is a program that builds a catalogue of objects from an
astronomical image. It is particularly oriented towards the reduction of large scale galaxy-survey
data, but it also performs well on moderately crowded star fields.
Its main features are:
\begin{itemize}
\item Support for multi-extension FITS.
\item Speed: typically 1--10 Mpixel/s or 10--1000 sources/s with a 2 GHz processor.
\item Ability to work with very large images (up to $65{\rm k}\times65{\rm k}$
pixels on 32 bit machines, or $2{\rm G}\times2{\rm G}$ pixels on 64 bit machines),
thanks to buffered image access.
\item Real-time match-filtering of images to improve detectability. \gam{This
jargon might not be understood until reading the entire documentation.}
\item Robust deblending of overlapping extended objects.
\item Flexible catalogue output of desired parameters only.
\item Pixel-to-pixel photometry in dual-image mode.
\item Fast Point-Spread-Function and galaxy model fitting.
\item Handling of weight maps and flag maps.
\item Optimum handling of images with variable S/N.
\item Built-in catalogue cross-identification.
\item Special mode for photographic scans.
\item XML VOTable-compliant catalogue output.
\end{itemize}

Back in the early nineties, the purpose of {\sc SExtractor} was to find a compromise
between refinement in both detection and measurements, and computational speed. By today's
standards, {\sc SExtractor} would be more accurately described as a quick-and-dirty'' tool.