how to measure photo stretch

Image processing, astrometry, photometry, etc.
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Morten Lerager
Posts: 67
Joined: 08 Oct 2021, 14:53
Location: Denmark

how to measure photo stretch

Post by Morten Lerager » 28 Feb 2022, 18:50

I have here 3 photo all taken with 120 sec.
From left to right ISO 100, 200 & 400
Raw loaded and auto stretch.
The goal is to find the noise sweet spot.
But how du I measure the stretch. I have been trying to measure the stars level, they should be equal, but that's not easy.
HEQ5 Pro 150PDS 60mm guide. Asiair.
Asi294mc. AA8.

fabdev
Posts: 461
Joined: 03 Dec 2018, 21:43

Re: how to measure photo stretch

Post by fabdev » 28 Feb 2022, 19:12

Hi Morten, is for your camera: ISO = Gain ?
Usually the problem of high Gain is earlier saturation.
The three images have a different visualization so they cannot be compared visually (looking for noise).
Try opening the three images in Astroart 8, then use the command "View / Equalize visualization" with option "Sigma" to display them with the same visualization. Then compare them with Blink.
Fabio.

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Morten Lerager
Posts: 67
Joined: 08 Oct 2021, 14:53
Location: Denmark

Re: how to measure photo stretch

Post by Morten Lerager » 02 Mar 2022, 20:55

Thank's Fabio
That was unknown to me, but exactly what i was looking for.
HEQ5 Pro 150PDS 60mm guide. Asiair.
Asi294mc. AA8.

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