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[bug #63171] Strange patterns on warped images

From: Pedram Ashofteh Ardakani
Subject: [bug #63171] Strange patterns on warped images
Date: Mon, 24 Oct 2022 04:00:41 -0400 (EDT)

Update of bug #63171 (project gnuastro):

                  Status:             In Progress => Fixed                  
             Open/Closed:                    Open => Closed                 


Follow-up Comment #19:

Hi all 👋

We've made the new commit [1] which discusses where these Moire patterns come
from, and some ways to mitigate/remove them in the 'Moire pattern and its
correction' section under 'Warp'.


Thanks to Mohammad's nice example demonstration in the Book [2] and the new
'--checkmaxfrac' option in Warp, we have a way to visually inspect the effect
- see (file jplus-warp-reg.jpg) and (file jplus-warp-reg-maxfrac.jpg), and
quantify it by interpreting the 'Statistics' of the 'MAX-FRAC' HDU which is
added to the Warped image if '--checkmaxfrac' is given, see [2].


Also, we can see that stacking the 'dithered' images helps resolve this issue
in the most precise way, potentially even *improving* the spatial resolution
of the image. It is worthy of note that stacking 'dithered' images can create
*deeper* images - see (file jplus-stack.jpg).

Please note that scales and limits are not exactly the same in the images
attached here, I tried to make them look similar. But you can make all of them
yourself following the instructions in [2].

Hopefully now things are making more sense. Please feel free to let us know
and continue the conversation if anything comes up.


(file #53899, file #53900, file #53901, file #53902)


Additional Item Attachment:

File name: jplus-warp-oversample.jpg      Size:575 KB

File name: jplus-warp-reg-maxfrac.jpg     Size:287 KB

File name: jplus-warp-reg.jpg             Size:448 KB

File name: jplus-stack.jpg                Size:439 KB


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