Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

PixInsight WBPP has been running for 60 hours

  • Please log in to reply
29 replies to this topic

#26 Rasfahan

Rasfahan

    Vanguard

  • -----
  • Posts: 2,275
  • Joined: 12 May 2020
  • Loc: Hessen, Germany

Posted 25 November 2022 - 09:59 PM

Maybe more succinct: If the brightness difference in the object is higher than the dynamic range of the camera you need to take subs of more than one exposure length (or gain). There are few targets that have parts you can adequately expose with 30s subs (on any camera/scope combination) and where that is not the case. 



#27 bobzeq25

bobzeq25

    ISS

  • *****
  • Posts: 31,183
  • Joined: 27 Oct 2014

Posted 25 November 2022 - 11:48 PM

But your Pleiades are actually a good example for the point I was making: You can clearly see the patterned read noise from your camera because your short exposures weren‘t sky limited (horizontal streaking). If you have that at f/2 with a more modern chip, taking 30s exposures at f/7 might not be the best strategy for the OP - unless the target is bright, in which case you don‘t need 1600 subs.

Just one of two possible data capture techniques.  There's an excellent discussion by Chris Woodhouse in the Astrophotography Manual.  He refers to the strategy of taking many short exposures as "Patience", the strategy of combining different exposures as "Cheat", referring to two card games.   You're suggesting "Cheat", I use "Patience".  Just a personal decision, one is not superior to the other.  There are a few high dynamic targets where multiple exposures do work better, but, in the general case, it's just a personal choice.



#28 Rasfahan

Rasfahan

    Vanguard

  • -----
  • Posts: 2,275
  • Joined: 12 May 2020
  • Loc: Hessen, Germany

Posted 26 November 2022 - 03:46 AM

Just one of two possible data capture techniques.  There's an excellent discussion by Chris Woodhouse in the Astrophotography Manual.  He refers to the strategy of taking many short exposures as "Patience", the strategy of combining different exposures as "Cheat", referring to two card games.   You're suggesting "Cheat", I use "Patience".  Just a personal decision, one is not superior to the other.  There are a few high dynamic targets where multiple exposures do work better, but, in the general case, it's just a personal choice.

I need to check that passage again, but I’m quite sure Mr. Woodhouse is referring to sky limited exposures. At 30s, f/7, you‘re not, in the general case of the camera in question if you choose a gain appropriate for the DR of most targets. Once you are sky limited, it is a personal choice with certain tradeoffs. But even in that case, I think it is valid to refer to a different imaging strategy if someone is mentioning that they can‘t deal with 1000+ subs with their current hardware.



#29 MikeECha

MikeECha

    Viking 1

  • *****
  • Posts: 608
  • Joined: 15 Sep 2018
  • Loc: Charlotte, NC

Posted 26 November 2022 - 09:35 AM

Ok, it's done and after nearly 110 hours of chugging the results are less than spectacular. No biggie; I know I had some crap frames in there. Lesson learned. What I have may be of good use in an HDR Comp.

 

However, as soon as it finished up, I immediately started working on the swap files. When I updated the OS hard drive, I must not have done a very good job because I stopped at 4 swap files. This time I kept adding by 2 swap files at a time and carefully checked, and rechecked, every incremental improvement. Here is what I started out with:

 

TqY0N7Y.jpg

 

And here is what I ended up with after adding going up to 17 swap files:

10hDdb6.jpg

 

So to summarize:

 

Total score: +3%

CPU: Virtually unchanged

Swap: +37%

Transfer: +37%

 

We'll see how things go next time I stack, but I am not going to use WBPP with LocalNorm for large stacks any longer. It ain't worth the wait!

You probably solved this by now but, just in case, make sure you update PI to the latest version. There have bee many improvements since.

 

I had the same problem with 3200 subs. The normalization process would do the R channel and the run for a week and would never finished the rest. I actually let it go to see how long it would take. MY PC never crashed. The Win10 resources were showing only 5% RAM usage (128GB available) and about 20% usage of my dual Xeon 24Core processors and 0% SSD activity. PI simply stopped running period.

 

There were no resource issues. There was something definitively wrong with the Normalization process in WBPP as I was able to run the same 3200-subs stack using NSG in a reasonable time (less that 24 hours). I read the PI forums and at the time there were several complaints about this issue that got the typical "you need a faster computer" or "run PI in Linux". I think that the problem is fixed now as I was able to run 1200 subs or so with no problem.

 

Unfortunately for me, after all this time, I found out that my flats were rotated as compared to the subs and it would make a mess of the integration. No big deal, M101 will be there in the same place next year.



#30 James Peirce

James Peirce

    Viking 1

  • *****
  • Posts: 645
  • Joined: 21 Aug 2020
  • Loc: Salt Lake City, Utah, United States

Posted 27 November 2022 - 11:05 AM

Here's why. Longer exposures can have drawbacks, I've seen that happen all the time here. Because people's intuition tells them longer must be better.

Subexposure fairly rapidly runs into a wall. Pixels saturate. Causes loss of star color, clips (blurs) highlights.

Total imaging time never runs into a wall (although there are diminishing returns). So more subs are _always_ better.

When I bought my F2 RASA, I knew I'd be using short subs to reduce pixel saturation. So I built a new processing computer to handle them. I routinely shoot hundreds of 10-30 second subs, even at Gain zero. Even then some pixels inevitably saturate, I try to limit the number to a few hundred in each frame.

There are certainly drawbacks to longer exposures which need to be balanced against other options, especially when the total quantity of exposures limits options for things like pixel rejection in post-processing or runs into limits based on mount or environment. Hard to comment on more since you haven’t shared specifics.

But “more subs are _always_ better” is wrong. Where the above doesn’t produce a limiting concern, the longer subs will produce dependably better results, and *especially* with fainter structures in exposures. Especially when it comes to signal that struggles to compete with sky glow, etc. And this is easy enough to test first hand.

On topic for the discussion, when we are talking about 20s subs, there are options available increase exposure time without losing data in highlights while at the same time mitigating considerable hardware and processing time concerns. I doubt anyone here got into this hobby because their favorite part is watching PixInsight chew through files for a morning and afternoon.

Even where exposures are as long as they can be without unacceptably compromising highlights, there are other options to consider for employing deeper exposures such as two sequences of exposures or shooting at a lower ISO.
  • Rasfahan likes this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics