[bug #63171] Strange patterns on warped images

[Raul Infante-Sainz]

URL:
  <https://savannah.gnu.org/bugs/?63171>

                 Summary: Strange patterns on warped images
                 Project: GNU Astronomy Utilities
               Submitter: infantesainz
               Submitted: Thu 06 Oct 2022 03:59:57 PM UTC
                Category: Warp
                Severity: 3 - Normal
              Item Group: Output not reasonable
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any


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Follow-up Comments:


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Date: Thu 06 Oct 2022 03:59:57 PM UTC By: Raul Infante-Sainz <infantesainz>
In Gnuastro 0.18.65-7933d, the output of warped images have strange patterns.
I found this issue when testing the new features on some images. Let me
reproduce and describe the problem step by step.

I attach an image to star with: 'img.fits'. It is a cropped region nearby to
the galaxy NGC 493. Image of 'float32' data type. Nothing special.

I convert this image to another one of type 'uint8'.


astarithmetic img.fits uint8 -o uint8.fits


Now just warp this image and have a look.


astwarp uint8.fits -o uint8-warp.fits

astscript-fits-view uint8.fits uint8-warp.fits


There is a clear pattern across the image, like an interference pattern.

If you are wondering why I am doing such a strange things, it is just because
I was warping bigger images and I found the same pattern (on normal 'float32'
images). Attached a screenshot (warped-float32.png). Then, when I tried to
upload the image to Savannah I had to decrease the size (by converting it to
integers). On this converted images the problem is even more clear.

To confirm that it is not a problem that comes from the original image I did
the following test: create an image with pure noise, warp and check it.


astarithmetic img.fits set-i i i - 3 mknoise-sigma -o noise.fits

astwarp noise.fits -o noise-warp.fits

astscript-fits-view noise-warp.fits









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File Attachments:


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Date: Thu 06 Oct 2022 03:59:57 PM UTC  Name: warped-float32.png  Size: 678KiB 
 By: infantesainz

<http://savannah.gnu.org/bugs/download.php?file_id=53803>
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Date: Thu 06 Oct 2022 03:59:57 PM UTC  Name: img.fits  Size: 1MiB   By:
infantesainz

<http://savannah.gnu.org/bugs/download.php?file_id=53804>

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