\subsection{Image Analysis}

\begin{description}

% \item[\htmladdnormallink{Astrometry}{http://www.roe.ac.uk/acdwww/gaia/astrometry.html}]
  \item[\xref{Astrometry}{gaia}{astrometry}]
   applying and displaying celestial coordinates to an image.

% \item[\htmladdnormallink{Photometry}{http://www.roe.ac.uk/acdwww/gaia/photom.html}]
  \item[\xref{Photometry}{gaia}{photom}]
   interactive measurements of selected stars using a circular or
   elliptical aperture.

% \item[\htmladdnormallink{Automatic object detection}{http://www.roe.ac.uk/acdwww/gaia/extract.html}]
  \item[\xref{Automatic object detection}{gaia}{extract}]
   automatic detection of the objects in an image.  A set of parameters
   (positions, brightness, ellipticity \emph{etc}\/) are computed for all
   the objects detected.

% \item[\htmladdnormallink{Surface photometry}{http://www.roe.ac.uk/acdwww/gaia/esp.html}]
  \item[\xref{Surface photometry}{gaia}{esp}]
   Surface photometry of galaxies, including determining radial profiles
   and fitting elliptical isophotes.

% \item[\htmladdnormallink{Image patching}{http://www.roe.ac.uk/acdwww/gaia/patch.html}]
  \item[\xref{Image patching}{gaia}{patch}]
   interactive removal of image blemishes and contaminating objects from
   an image.  For example, foreground stars might be removed from a
   galaxy image.

% \item[\htmladdnormallink{Properties of image regions}{http://www.roe.ac.uk/acdwww/gaia/regions.html}]
  \item[\xref{Properties of image regions}{gaia}{regions}]
   statistics, extraction and removal of shaped regions of an image.

% \item[\htmladdnormallink{Image comparison}{http://www.roe.ac.uk/acdwww/gaia/compare.html}]
  \item[\xref{Image comparison}{gaia}{compare}]
   two images can be compared by either plotting one as a set of contours
   superimposed on the other or by blinking between the two images ({\it
   cf}\/ the `blink comparator' used to compare two photographic plates).

% \item[\htmladdnormallink{Object position and statistics}{http://www.roe.ac.uk/acdwww/gaia/statistics.html}]
  \item[\xref{Object position and statistics}{gaia}{statistics}]
   two-dimensional Gaussian fits to single or multiple objects.

% \item[\htmladdnormallink{Polarisation}{http://www.roe.ac.uk/acdwww/gaia/polarimetry.html}]
  \item[\xref{Polarisation plotting}{gaia}{polarimetry}]
   polarisation maps can be plotted, regions selected from them \emph{etc}.
   These facilities are intended to be used in conjunction with the
   POLPACK package for polarimetry and spectropolarimetry (see
   \xref{SUN/223}{sun223}{}\cite{SUN223}).

% \item[\htmladdnormallink{Profiles of rectangular regions}{http://www.roe.ac.uk/acdwww/gaia/xyprofile.html}]
  \item[\xref{Profiles of rectangular regions}{gaia}{xyprofile}]
   Interactive averaged profiles along the $x$\/ and $y$\/ axes of a
   rectangle.

\end{description}

