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| xyz |
11/02/2015 08:24AM (Read 924 times)
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Status: offline
Registered: 10/30/2015
Posts: 1
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How background is calculated using "centroid" option in "fitskypars" sub-task in "phot" task ?
I have read IRAF help page. But it did not describe the details.
Help says: "Compute the intensity weighted mean of the sky pixel histogram."
What does this mean in detail ?
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| fitz |
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11/04/2015 06:28AM
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Status: offline
Registered: 09/30/2005
Posts: 4040
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The details are described by an algorithm more than an equation I can easily reproduce here. The description for the procedure used is:
# AP_CENTROID -- Procedure to find the mode, width and skew of the sky
# distribution by computing the moments of the histogram.
and you can find the code in $iraf/noao/digiphot/apphot/fitsky/apcentroid.x if you want to trace through the details. AFAIK, all the background calculations take into account fractional pixels in the apertures. You should also be aware that the FITSKY task exists to compute just the sky values if you want to check parts of the image, however the same algorithm appears to be used from the PHOT task using centroid. Hope this helps.
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