[bug #62702] Clumps on strong gradients of larger galaxies become too large

[Mohammad Akhlaghi]

URL:
  <https://savannah.gnu.org/bugs/?62702>

                 Summary: Clumps on strong gradients of larger galaxies become
too large
                 Project: GNU Astronomy Utilities
               Submitter: makhlaghi
               Submitted: Mon 04 Jul 2022 12:29:31 AM BST
                Category: Segment
                Severity: 3 - Normal
              Item Group: Output not reasonable
                  Status: In Progress
                 Privacy: Public
             Assigned to: makhlaghi
             Open/Closed: Open
         Discussion Lock: Any


    _______________________________________________________

Follow-up Comments:


-------------------------------------------------------
Date: Mon 04 Jul 2022 12:29:31 AM BST By: Mohammad Akhlaghi <makhlaghi>
When a clump falls on the gradient of a large object, in the current
implementation of Segment, it will steal a large fraction of flux from the
large object. The code below in the P.S can be put in a simple shell script to
reproduce the problem. 

P.S. Code to reproduce the problem.


# Parameters.
oversample=5
zeropoint=22
background=20

# Abort in case of an error.
set -e

# Make a build directory if it doesn't already exist.
if ! [ -d build ]; then mkdir build; fi

# Generate the catalog
cat=build/cat.txt
echo "1 0   0   2 3  2.8 0 1   5  5"  > $cat # PSF
echo "1 100 100 1 15 1   0 0.4 9  5" >> $cat # Galaxy
echo "1 110 100 4 0  0   0 0   13 0" >> $cat # Star

# Build an image and a convolution kernel.
psf=build/psf.fits
raw=build/raw.fits
astmkprof $cat --mergedsize=200,200 \
          --zeropoint=$zeropoint -o$raw \
          --oversample=$oversample
mv build/0_raw.fits $psf

# Convolve the image with the kernel.
conv=build/conv.fits
astconvolve $raw --kernel=$psf -o$conv

# Undersample the convolved image.
nonoise=build/no-noise.fits
astwarp $conv --centeroncorner --scale=1/$oversample \
        --output=$nonoise

# Add noise
noised=build/noised.fits
export GSL_RNG_SEED=1657794821
astarithmetic $nonoise $background $zeropoint \
              mag-to-counts mknoise-poisson \
              -o$noised --envseed

# Detect the signal
det=build/detected.fits
astnoisechisel $noised --tilesize=10,10 -o$det

# Segment the signal
seg=build/segment.fits
astsegment $det -o$seg







    _______________________________________________________
File Attachments:


-------------------------------------------------------
Date: Mon 04 Jul 2022 12:29:31 AM BST  Name: large-clump.png  Size: 62KiB  
By: makhlaghi

<http://savannah.gnu.org/bugs/download.php?file_id=53390>

    _______________________________________________________

Reply to this item at:

  <https://savannah.gnu.org/bugs/?62702>

_______________________________________________
Message sent via Savannah
https://savannah.gnu.org/