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Дата изменения: Wed Oct 22 17:31:26 2008
Дата индексирования: Tue Aug 18 14:53:53 2009
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XMM-Newton Science Analysis System


omdetect (omdetect-5.14.2) [???]

Meta Index / Home Page / Background image

Background algorithm

The alogorithm works as follows.

1. Compute the mean value of the whole image, using a clipping algorithm.
2. Divided the image into boxes of size 100 by 100 pixels.
3. For each box
   1. Obtain a list of pixels with a value less than maxheight
   2. loop through all the pixels in the box and obtain a list of the ``usable'' background pixels within a box of size 100
      binx $\times$ 100
      binx + 1 pixels
   3. Find the median of the list of pixels and set the background pixel to this value

   Note that within each box the list of background pixels at each pixel does not have to be sorted to obtain the median- the algorithm initially sorts all the ``background'' pixels within the box and then uses a specially constructed algorithm to determine the median from the list of pixels within the box around the pixel, thus reducing the cpu time by a considerable amount.