raw_merge with #shots > 10

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raw_merge with #shots > 10
« on: 13 / July / 2015, 05:21:41 »
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Hi guys,

First of all, great--really great work! Thank You so much!

After fiddling with the LUA table handling ("nil"), I managed to have a working script to average 50 shots in camera using raw_merge_... Alas, when trying more than 10, namely 50 shots the outcome looks a bit psychedelic. I argue this is because of limitations of the internal pixel buffer. Say, if they were of 16 bit type I'll pretty sure and pretty soon get the digital values, summed up, bounce against MAX.

Would You mind to denote that limitation in the documentation?

Could You think of a workaround? If it were possible to calculate with floating point types internally that prob would be levered out.

Thanks a lot!



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Re: raw_merge with #shots > 10
« Reply #1 on: 13 / July / 2015, 22:25:23 »
Say, if they were of 16 bit type I'll pretty sure and pretty soon get the digital values, summed up, bounce against MAX.
Better yet, they probably wrap around ;)

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Would You mind to denote that limitation in the documentation?
The official documentation is the wiki, which anyone can edit. I can confirm the merge operations use unsigned 16 bit numbers.

Note that the raw may be 10 (mostly old digic II/III cameras), 12 (most cameras), or 14 (g1x)  bits, so the number of images it takes to overflow will vary.

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Could You think of a workaround? If it were possible to calculate with floating point types internally that prob would be levered out.
Averaging in groups should be roughly equivalent: e.g. average 5 sets of 10 images, and then average the resulting 5.

It wouldn't be hugely difficult to use a different type in the code (see modules/raw_merge.c in the source), but I'm not sure it's worth it. If you are serious about this kind of thing, you are probably much better off doing it on a PC.
Don't forget what the H stands for.

Re: raw_merge with #shots > 10
« Reply #2 on: 08 / October / 2015, 06:52:28 »
Modulo HDR can be reliably recovered
http://web.media.mit.edu/~hangzhao/modulo.html

Even if you do average 50 frames, maybe that's not what you want, to ideally reduce noise.
https://en.wikipedia.org/wiki/Dark-frame_subtraction

There's ways better than averaging, like sigma-kappa, a combination of median and average.  Also note that many short exposures may be better than fewer long exposures.

http://www.clarkvision.com/articles/image-stacking-methods/

 

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