Brightness compensation in ZereneStacker

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AlxndrBrg
Posts: 78
Joined: Tue Jan 14, 2014 12:17 pm

Brightness compensation in ZereneStacker

Post by AlxndrBrg »

Maybe this is a known behavior in ZS, but I thought I'd post it here anyway since the difference was so drastic.

My setup uses constant lighting, so there is no real reason why I should use the brightness compensation, just kept it on since figured it it could help some if one of my Jansjö's got bumped during a stack. Will be keeping that setting off from now on...

I'm just showing the PMax here, but the DMap was identical.
Image

SebastianFg
Posts: 23
Joined: Mon Oct 09, 2017 10:24 am
Location: Freiberg, Germany

Post by SebastianFg »

Thank you for the hint, I didn´t know it and I will test it.
Best regards,
Sebastian

rjlittlefield
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Post by rjlittlefield »

To explain what's happening...

Brightness correction in Zerene Stacker is done by levels-adjusting each frame so that the mean and variance of all pixels in the frame is the same for all frames.

The master frame for this process is the first frame in the list (after automatic reversal if that's done).

This approach works well when all frames in the stack have similar overall appearance, typical of short stacks.

However, it can have the effect shown here for deep stacks where various portions of the stack look quite different from each other.

For example if the first frame happens to show mostly light background, with hardly anything in focus to be dark, then it will be bright and low contrast (large mean, small variance). After adjustment, all the other frames will be bright and low contrast also, producing a final result that is brighter and lower contrast than it should be.

Obviously it would be better if brightness adjustment removed frame-to-frame variations that are due to actual exposure differences, while retaining overall variations that are due to changes in focus and framing. That's on the infamous list of future improvements, but there's no schedule because so far I haven't been able to figure out the math to do it properly.

Best approach is to use continuous illumination, with a shutter speed that is slow enough to avoid mechanical variation in shutter open time.

--Rik

Lou Jost
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Post by Lou Jost »

Could you just take a moving average of nearby frames? Edit: No, that wouldn't give you perfect correction of each frame but it would help...

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