Background determination

The estimate of an accurate background is essential to determine the magnitude of faint sources. At this purpose, we have decide to adhere as much as possible to the SExtractor algorithms to compute the background of each object, and implemented several options to deal with this task. In particular, both for the detection and the measure image, the user can select one of these three options:

  1. use as input a background-subtracted image, therefore relying on other applications (such as SExtractor itself) to compute the background. This option saves computing time and can be adopted when the background is quite homogeneous.
  2. use the backgorund value computed for each object by SExtractor, as stored in the input catalog.
  3. Compute the background within ConvPhot: in this case, the background is computed in a ``rectangular annulus'' around the object, of size set by the user. Nearby objects are masked out using the (dilated) segmentation map (Fig.2). As a background estimator, we follow the SExtractor approach that uses either the median or the mode according to the σ-clipping results.
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