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eSASS task: ermask



This document provides a description of the algorithm and instructions for the correct usage of the ERMASK task, which is part of eSASS (the eROSITA Science Analysis Software System).


Create detection masks for eSASS detection chain tasks defining valid image areas which are suitable for detection. The masks are based on exposure maps created by the task EXPMAP.


The task ERMASK evaluates an exposure map and calculates a detection mask according to conditions specfied by parameters threshold1 and threshold2 . The detection mask is written into the primary extension FITS extension of the output image ( int8 ) , valid pixels are set =1, pixels to excluded from source detection are set =0.

Parameter threshold1 defines an exposure threshold, given as fraction of the maximum exposure value:

  detmask(x,y) = 0
  if (expimage(x,y) > maxval(expimage)*threshold1) detmask(x,y) = 1
With parameter threshold2 additionally a maximum local exposure gradient can be set:
  if (sqrt((expimage(x+1,y)-expimage(x-1,y))**2 + (expimage(x,y+1)-expimage(x,y-1))**2) > expimage(x,y)*threshold2 ) detmask(x,y) = 0
The detection pipeline requires only detection mask, if images from the same instrument in several energy bands are processed.


Input files:

Output files: