HDR Stacking

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jdaliix
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HDR Stacking

Post by jdaliix » Fri May 10, 2019 7:46 pm

This is only a dream of mine, and I don't expect it to happen, but I'll post anyway. I'm not sure I'm correct in the lingo with respect to HDR, but I'll try to briefly explain. Miloslick is camera capture software exclusive to Mallincam's CCD cameras. The guy who does that promised a version for CMOS cameras in January, but hasn't done it, and no updates as to status. In that software he had a utility for stacking he called HDR (high dynamic range) stacking, which for his software enabled additive stacking (as opposed to averaged), only the exposures would increase in length for each succeeding frame. So it could be set to do a 3 second, then a 6, then 12, then 18, decided by 1/4 stops, 1/2 stops, etc. With additive, it made it so short exposures got a lot done. The beauty of the setup is that it would GREATLY limit the brightness of bright galactic cores, for example, while brining in far more detail in the fainter features. It worked marvels on, for example, greatly limiting the overexposure of Orion's trapezium while bringing in all the nebulosity. Other than it is for CCDs, it would capture more faint details (galactic arms, etc.) than anything I've ever used to date.

Is it even remotely possible to get something like this?

Thanks,

-- Jason

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admin
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Re: HDR Stacking

Post by admin » Fri May 10, 2019 8:26 pm

Hi,

An interesting idea – I'm not sure exactly what algorithm you use to blend the different exposure images together, although if you are starting with the shortest exposures and going longer then one approach would just be to ignore new data in pixels that were saturated (overexposed) and scale the data down by the ratio of current exposure to initial exposure.

The question I'm going to ask though is how big is the requirement for this. It only makes sense if the recommended sub exposure length (using the brain or the 10 times read noise squared upon sky brightness rule) is long enough to saturate the brighter parts of the target. I have a sneaking suspicion that for many or most observers that might only be true for two targets – M 31 and M42. It will be interesting to validate that suspicion or not though.

Cheers, Robin

jdaliix
Posts: 10
Joined: Mon Jun 11, 2018 2:01 am

Re: HDR Stacking

Post by jdaliix » Sun May 12, 2019 2:08 am

I use an ASI294 and a few others. I imagine SharpCap was really originally designed for DSLR type cameras and longer term exposures than the 40 second max needed for EAA type cameras? If I wanted to get the faintest detail out of, say, M81, I'd have to expose it for, say, 90 seconds, but if I did that, the core would be far too bright. Same with something like M51, even the Whale. With Miloslick, it would have taken 4-5 additive exposures, the last one being 30 seconds, for a total of 80 seconds and you'd have more detail in the image than you'd ever seen with CCD or CMOS "video" cameras, while the core would remain "manageable." As mentioned, the problem with Miloslick is that it's only for Mallincam CCDs, and I enjoy feeding the images onto a 40" plasma TV and viewing in 3D. They're spectacular images, but they'd be better with a utility that functioned like that in Miloslick.

Anyhoo...thanks for the musings.

-- Jason

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Re: HDR Stacking

Post by admin » Thu May 16, 2019 5:53 pm

Hi,

Thanks for the feedback. I will consider this for the next major version as it sounds like a fun feature to have. It might initially be a partial implementation which would require the exposure to be changed manually but with the stacking algorithm capable of dealing with exposure variation.

Cheers, Robin

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