Live Stack - High Dynamics

[aquariusCZ]

Hi Robin,
LiveStack is a really powerful tool.
And the nice new features (meteor, comet) in version 4.1.

I propose one more new function "High Dynamics" (actually inverse to meteor, possibly inverse Sigma).
Live Stack would not stack pixels with a higher value than specified (eg 250).

After launch Live Stack -"High Dynamics", it would start with a short exposure that would not burn out the stars.
The exposure time would be gradually added (increasing the gain) and the darker parts of the image would be drawn.
Burned pixels would not draw.

Stack_166frames_238s.jpg (136.8 KiB) Viewed 1636 times

M42 2/9/2023 9:26 PM
!!!!! Photographed from a tripod. Without astro mounting !!!!!
Samyang 135/2, ASI 178MM, Optolong L-Pro, MONO8, bin2x2, exp. 1.4s, gain 380,
166 exposures Live Stack, PaintNet editing

Frýdlant nad Ostravicí

The new feature would improve the display of the Trapezium.

[admin]

Hi,

yes, I agree - I have considered this approach of gradually increasing exposure and throwing away any saturated data - I think it would work.

However, often the issue turns out to be that the stretch applied tends to make the brighter areas show as 100% brightness. There are a couple of ways to improve this...

1) In SharpCap 4.0, use a weaker stretch in live stacking and also a display stretch - this double stretch approach seems to help bring out a wider range of detal

2) In SharpCap 4.1 beta there is now a 'stretch mode' option. Stretch modes higher than 2 help bring out wider dynamic ranges than normal into a usable image, avoiding the overexposed core problem.

thanks,

Robin

[aquariusCZ]

Hi Robin,
thanks for advice. In version 4.1, the higher "Stretch Mode" really reduces overburns during longer exposures. However, the histogram moves to the right with additional images with an even longer exposure, and after more images, overburns appear.
Best regards
Thomas

[admin]

Hi Thomas,

that's odd - the live stack histogram should stay basically stationary if all the frames are the same in terms of exposure/gain/etc... It should only move if you start adding frames with different settings to an existing stack. If it is shifting for you in every stack then it may be worth trying to work out why.

Anyway, sorry to hear that the stretch modes didn't help much - I added them because I had the same issues with an M42 stack that was either losing the faint nebulosity or blowing out the core, and found that the higher modes definitely improved things (as long as the core is not blown out in your individual frames).

The HDR thing is still on the future features list, but no real idea of when.

cheers,

Robin

[aquariusCZ]

Hi Robin,
this is a misunderstanding, "Stretch Mode" really improves the image in more exposed parts of the image. I'm still experimenting with adding exposure time while shooting a single stack. With a higher "Stretch Mode", the image will burn after a much larger number of exposures.
I look forward to the eventual implementation of HDR.

Thomas

[aquariusCZ]

15.2.2023 18:43

Stack_392frames_272s.jpg (193.22 KiB) Viewed 1496 times

"Stretch Mode" 6

[aquariusCZ]

Hi Robin,
I thought of using sigma clipping for HDR. Start with a brighter image and add burnt areas at the end.
Thomas
So I tried Sigma. HDR works well with the Sigma, but it maps in the picture. I have the best result with Default Stacking.

[AstroLaptop]

Hi Robin
You and your program are absolutely marvellous. I came looking for advice on live stacking a comet (which I found thank you) and ended up here. I didn't know I needed this info until I found it!