how to measure photo stretch

[Morten Lerager]

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.

[fabdev]

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.

[Morten Lerager]

Thank's Fabio
That was unknown to me, but exactly what i was looking for.