Share:
Notifications
Clear all

19 June 2021: Our upload server https://upload.astropixelprocessor.com/ has been migrated successfully to our new office with higher upload and download speeds (nearly 10MByte/sec up/down ) ! We now have 1 general upload user called: upload with password: upload. The users upload1 - upload5 have been disabled.

31 May 2021: APP 1.083-beta2 has been released ! APP 1.083 stable will follow soon afterwards. It includes a completely new Star Reducer Tool, New File Saver Module, Improved Comet registration and much more, check the release notes here!

DOWNLOADS are available HERE!

 

Drizzle (mono)  

  RSS

 Axel
(@axel)
White Dwarf Customer
Joined: 4 years ago
Posts: 19
June 13, 2021 18:12  

Hi,

I have a hard time using drizzle (mono) with a set of 75 frames. I get weird kind of "bayer - pattern" like in the background.

I used the following settings : droplet 0.5 scale 2.0. Note that I usually use these settings without 0 trouble and that for another panel shot in the same conditions and about the same number of frames  as the problematic set I get excellent drizzling results.

image

I tried to up droplet up to .85 and it seems to be back on track.

Is there a way to pre-determine the right droplet on a given set or it is more an iterative approach?

Any advice I should be aware of?

CS!

Axel


ReplyQuote
(@vincent-mod)
Universe Admin
Joined: 4 years ago
Posts: 3550
June 14, 2021 10:17  

Not really to my knowledge (going to 0.5 makes sense, but it does have the best result when you're undersampled), can you post a screenshot of the other panel that did work nicely? Just for me to get a better idea..


ReplyQuote
 Axel
(@axel)
White Dwarf Customer
Joined: 4 years ago
Posts: 19
June 14, 2021 12:06  
Posted by: @vincent-mod

Not really to my knowledge (going to 0.5 makes sense, but it does have the best result when you're undersampled), can you post a screenshot of the other panel that did work nicely? Just for me to get a better idea..

Dear Vincent,

As for the 0.5 droplet I use it as refered in the help box :" droplet.5 with scale x2 is similiar to drizzle in other software" (thinking of PI I guess).

If you have  a good guidance as how to approach drizzling at 4.4"/px, I'll be happy to adjust my processing.

Here is another panel with 0.5 / x2 that came out clean

image

BR,

Axel


ReplyQuote
(@vincent-mod)
Universe Admin
Joined: 4 years ago
Posts: 3550
June 14, 2021 14:44  

Yes, so that's why the 0.5 is kind of a good starting point. I'm not sure if it works well on your pixel-scale, I'll ask Mabula to answer here. 🙂


Axel liked
ReplyQuote
 Axel
(@axel)
White Dwarf Customer
Joined: 4 years ago
Posts: 19
June 19, 2021 18:04  

Hi Vincent,

Any feedback from Mabula?

 


ReplyQuote
(@vincent-mod)
Universe Admin
Joined: 4 years ago
Posts: 3550
June 19, 2021 18:46  

Hi Axel, not yet sorry, busy times. I've notified him again.


ReplyQuote
(@mabula-admin)
Universe Admin
Joined: 4 years ago
Posts: 2641
June 19, 2021 20:12  

Hi Axel @axel,

I think that the pattern that you are getting is clearly due to drizzle artefacts... and if the drizzle droplet size increase solves it, it is confirmation that the artefacts are due to incomplete drizzle... So it likely means that

  1. the data is not enough dithered or
  2. the amount of data is still to small or
  3. the data is not that undersampled this time due to very bad atmospheric conditions possible... (seeing of 4-5" does occur on bad nights).

How much did you dither between the frames? How are the star sizes compared to the other datasets?

If on other datasets with the same amount of frames the artefacts are not there then the reason must be somehow in the data itself. Drizzle will only work nicely if all 3 drizzle conditions are satisfied 😉

What you could do as well, do not drizzle in this case, simply set scale to 2.0 and use data interpolation if you want the higher resolution. It might work better than drizzling on this particular dataset.

Another thing that you could try, is to alter the drizzle kernel. Which kernel did you use? It is mentioned in the FITS header of the stack.

Mabula

 


ReplyQuote
 Axel
(@axel)
White Dwarf Customer
Joined: 4 years ago
Posts: 19
June 19, 2021 23:56  

@mabula-admin Hi Mabula,

Thanks for your feedback.

I try to answer your points

dither : I use unguided tracking but in SGP I use Direct Mount Guider set to a dither of  1sec impulse  every 3 frames . Never get walking noise doing so but may be it is not enough for drizzle.

number of frames : 75 in this case over 5 nights

quality of the panel wrt to other panels   : I randomly picked 3 frames from each night of this panel and ran star analysis and compared to  3 frames from each night for another panel (I shot 4 panels a night). I've got close results in terms of data shape.

seeing : can't tell tbh.

image

Best

Axel


ReplyQuote
Share: