Flats flip

Image processing, astrometry, photometry, etc.
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Morten Lerager
Posts: 69
Joined: 08 Oct 2021, 14:53
Location: Denmark

Flats flip

Post by Morten Lerager » 09 Dec 2022, 19:17

When show a flat frame in Asiair I see a little artifact from the sensor. It's show up in the upper right corner at the sub frame.
When I open the fits in AA8 the artifact are now in the lower right corner of the picture.
Why is that? . Asiair nor AA8 know how the picture was taken. Mount turned off, no plate solve.
And I gess dark frame is the same.
Should I just forget and hope light, Darks, Flats come out nicely :shock:

I don't know witch way is the correct way, yet.
HEQ5 Pro 150PDS 60mm guide. Asiair.
Asi294mc. AA8.

fabdev
Posts: 478
Joined: 03 Dec 2018, 21:43

Re: Flats flip

Post by fabdev » 09 Dec 2022, 20:59

Hi, probably all lights, flats and darks FITS files are incorrectly saved vertically flipped, but you can safely preprocess the whole sequence and flip the result after preprocessing.
To avoid the problem, you could ask the software manufacturer to support the ROWORDER keyword, see:
https://free-astro.org/index.php?title= ... rientation

If ROWORDER is not present, Astroart 8 uses the correct FITS orientation (bottom-up). You can verify the correctness opening your images with any FITS viewer, see:
https://fits.gsfc.nasa.gov/fits_viewer.html (I recommend DS9)

Using the correct FITS orientation guarantees that if you make a discover and you send the image to a professional observatory or institute, it will be displayed as you intended, since all academic software under Unix/Linux uses the same FITS orientation (bottom-up).

A quick on-line viewer to verify FITS files:
https://www.clearskyinstitute.com/fits/fits.html
Fabio.

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Morten Lerager
Posts: 69
Joined: 08 Oct 2021, 14:53
Location: Denmark

Re: Flats flip

Post by Morten Lerager » 09 Dec 2022, 21:25

Great info Fabio.
I will inspect the Asiair fits for ROWORDER bottom up.
If needed I could insert the code by a macro.
HEQ5 Pro 150PDS 60mm guide. Asiair.
Asi294mc. AA8.

fabdev
Posts: 478
Joined: 03 Dec 2018, 21:43

Re: Flats flip

Post by fabdev » 09 Dec 2022, 22:15

OK, actually ROWORDER "top-down" is fine as well.
The problem is when ROWORDER is completely missing.
Clear skies, Fabio.

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