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Background Subtraction issue when swarping
06-09-2017, 21:57
Post: #1
Background Subtraction issue when swarping
Hi all,

I have a question related to the background subtraction of SWarp (v2.38.0). I was trying to combine a list of images into a single mosaic. Hence I would like to subtract the background of each of them then combine them together with average or median.

But what I noticed is that the background is only subtracted for the first image in the list, or at least that's what the output of Swarp indicated.


In the config file I have the following:


#--------------------------- Background subtraction ---------------------------

SUBTRACT_BACK Y # Subtraction sky background (Y/N)?
# (all or for each image)

BACK_TYPE AUTO # AUTO or MANUAL
# (all or for each image)
BACK_SIZE 128 # Background mesh size (pixels)
# (all or for each image)
BACK_FILTERSIZE 3 # Background map filter range (meshes)
# (all or for each image)
....



Below is the SWarp output of all these images, as you can see only the first one show a non-zero background value. Are there some flags that I need to add to enable background subtraction for all of the input images? Thanks in advance for your reply!


----- SWarp 2.38.0 started on 2017-06-09 at 13:10:47 with 8 threads

------- Output File coadd.fits:
"no ident" WEIGHTED no ext. header 37821x37804 32 bits (floats)
Center: 10:00:59.49 +02:13:53.0 106'x106' Scale: 0.168 ''/pixel
Gain: 0 e-/ADU Flux scaling (astrom/photom): 1 X / 1 X

-------------- File 9813-0_3_img.fits:
"no ident" WEIGHTED no ext. header 4100x4200 32 bits (floats)
Center: 10:03:58.24 +02:02:40.5 11.5'x11.8' Scale: 0.168 ''/pixel
Gain: 0 e-/ADU Flux scaling (astrom/photom): 0.9998 X / 1 X
Background: 0.00555533 RMS: 0.1051587 Weight scale: 1

-------------- File 9813-0_4_img.fits:
"no ident" WEIGHTED no ext. header 4100x4200 32 bits (floats)
Center: 10:03:58.26 +02:13:52.5 11.5'x11.8' Scale: 0.168 ''/pixel
Gain: 0 e-/ADU Flux scaling (astrom/photom): 0.9998 X / 1 X
Background: 0 RMS: 1 Weight scale: 1

-------------- File 9813-0_5_img.fits:
"no ident" WEIGHTED no ext. header 4100x4200 32 bits (floats)
Center: 10:03:58.29 +02:25:04.4 11.5'x11.8' Scale: 0.168 ''/pixel
Gain: 0 e-/ADU Flux scaling (astrom/photom): 0.9998 X / 1 X
Background: 0 RMS: 1 Weight scale: 1

-------------- File 9813-0_6_img.fits:
"no ident" WEIGHTED no ext. header 4100x4200 32 bits (floats)
Center: 10:03:58.31 +02:36:16.3 11.5'x11.8' Scale: 0.168 ''/pixel
Gain: 0 e-/ADU Flux scaling (astrom/photom): 0.9998 X / 1 X
Background: 0 RMS: 1 Weight scale: 1

-------------- File 813-0_7_img.fits:
"no ident" WEIGHTED no ext. header 4100x4200 32 bits (floats)
Center: 10:03:58.33 +02:47:28.2 11.5'x11.8' Scale: 0.168 ''/pixel
Gain: 0 e-/ADU Flux scaling (astrom/photom): 0.9998 X / 1 X
Background: 0 RMS: 1 Weight scale: 1

....
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09-25-2017, 23:19 (This post was last modified: 09-25-2017 23:22 by oleg_astro.)
Post: #2
RE: Background Subtraction issue when swarping
Hi,
you can try THELI GUI.
It is a grafical interface for Astromatic tools.

My OS is Ubuntu Astronomy 16.04 (64-bit) http://ubuntuastronomy.ap-i.net
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