Which histogram to use while live stacking?

Discussions of Electronically Assisted Astronomy using the Live Stacking feature.
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Natalie Electron
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Which histogram to use while live stacking?

Post by Natalie Electron » Thu Feb 13, 2020 4:44 pm

Hi,
When I have live stacking on, it appears that I can make adjustments to either the histogram in the live stacking tab, as well as in the normal right side camera controls, but they seem to have different effects, and I get weird results with I adjust both of them.

What functionality differences do these two histogram controls have ?
Which one should I use when live stacking ?
Is the one on the right just for the current capture and the live stacking one for the combined stacked image?
Should I only use one or the other ?

Thanks,
Nat

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admin
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Re: Which histogram to use while live stacking?

Post by admin » Thu Feb 13, 2020 10:36 pm

Hi,

Usually you should use the controls in the live stacking panel to make adjustments in this situation and leave the mini histogram on the right-hand side set the defaults. There really is nothing to stop you from using both, but as you've noted if you aren't careful you can end up getting some weird results by trying to use both at the same time.

Cheers, Robin

donstim
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Re: Which histogram to use while live stacking?

Post by donstim » Tue Feb 18, 2020 12:02 am

I've wondered the same thing for quite a while. I haven't yet heard a good explanation of why one should choose to use both, though I know imagers I respect highly (Chris for one) do so. As I understand from the manual, if you use both and want to save the image as you see it on the screen, you must "Save exactly as seen" and this choice limits one to an 8-bit representation. If you use only the livestack histogram, you can save the image you see on the screen via the "Save with adjustments," which, if your camera supports it, saves it as a 16-bit representation.

It can be difficult to directly see the effect of moving the livestack sliders on the histogram of the displayed image since, as stated in the manual:
"Changes made to the levels here do not affect the shape or position of the histogram shown in the Live Stacking panel, but will show in the Mini Histogram in the Camera Control Panel on the right." However, since these changes are reflected in the Display Histogram on the right (also referred to as the Mini Histogram), one can stretch the image using the livestack histogram sliders while observing and getting feedback by seeing the effect on the display mini histogram.

One good reason to use the display histogram sliders in addition to the livestack sliders, however, became apparent to me in watching this video: https://www.youtube.com/watch?v=S-2vueDiEqw&t=1856s. After an initial stretch using the livestack sliders, these sliders were so close together it would be difficult to adjust them further. The display mini-histogram was like a zoomed in view that enables more "granularity" in further stretches.

I remain concerned, though, about the potential loss of dynamic range in the saved 8-bit PNG file when saving the display mini- histogram adjustments compared to the saved 16-bit PNG file when just using and saving the livestack histogram adjustments, particularly when using that saved file for further processing.

Comments on the above would be welcome.

BlackWikkett
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Re: Which histogram to use while live stacking?

Post by BlackWikkett » Tue Feb 18, 2020 2:41 am

Nat,

In the past while live stacking I would use both the live stack histogram along with the display histogram. This was done mainly to compensate for color balance. I leave the red and blue pre-processing color balance sliders at the 50% default. In older versions of SharpCap the histogram peaks would not align in the live stack histogram but would align in the display histogram once you color balanced the live stack. I would get an initial auto stretch in the live stack histogram controls then fine tune the display histogram since the smaller histogram reflected the color balance. Since SC version 3.2.6185 the live stack histogram reflects the color balance adjustments made in live stacking color controls. Since that change I've started using Just the live stack histogram and leaving the display histogram at it's defaults. The larger histogram gives much more granular control. While live stacking I my play around with the display histo but it goes back to defaults once I'm ready to save the image.

An other advantage is not using the display histo lets you "save with adjustments" which is what you see at the time of save but in 16 bit not 8 bit.

-Chris

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