Author Topic: Always splotchy background pollution? Help!  (Read 1183 times)

Offline DuaneDibbley

  • Newcomer
  • Posts: 1
    • View Profile
Always splotchy background pollution? Help!
« on: 2019 November 02 20:40:10 »
Hi all,

I am quite new to astro and have been imaging using 100mm refractor on HEQ5 mount with PHD2 guiding. I image with a Canon 70D. On almost all of my imaging I seem to get a splotchy yellow background in parts. I've always assumed it to be light pollution but I have never successfully managed to remove it. I borrowed a friends Astronomik CLS CCD clip in filter to see what effect it might have but my first outing with it and there seems to be little difference in controlling this 'splotchiness'.



This is a screenshot of what I'm talking about (low quality with autostretch).

https://www.dropbox.com/s/2wqzynr1ff2tqai/helix_splotchy.xisf?dl=0is a link to the xisf of the bias, dark and flat corrected integrated and drizzled and cropped image.

Any advice on technique? I try to follow the light vortex astronomy tutorial for DBE and I never really seem to make much of a difference. I've even tried splitting into individual RGB channels. Makes me wonder if what I'm trying to correct isn't actually corrected by the tools I'm using because it's something else?

Offline pfile

  • PTeam Member
  • PixInsight Jedi Grand Master
  • ********
  • Posts: 4691
    • View Profile
Re: Always splotchy background pollution? Help!
« Reply #1 on: 2019 November 02 22:20:48 »
DBE could help but given the lumpiness you might need a lot of samples to capture it all.

this technique: https://pixinsight.com/forum/index.php?topic=5498.msg37760#msg37760

works pretty well. the idea is that you protect the foreground and then use the AtrousWavelets tool to blow away the chrominance information at the larger scales in the background. while this doesn't fix the blotchiness per-se, it makes it a heck of a lot less noticeable to the eye.

rob


Offline wimvb

  • PixInsight Enthusiast
  • **
  • Posts: 91
    • View Profile
    • Wims place
Re: Always splotchy background pollution? Help!
« Reply #2 on: 2019 November 03 01:32:59 »
The recipe I use to remove colour noise in the background is as follows:

Extract luminance from the linear image.

Stretch this with stf settings and increase the background level to 50% with curves.

Apply inverted as a mask to the colour image.

Open MMT and set working mode to chrominance (restore Y). Also select about 8 layers.

Set high noise reduction parameters, first layer gets a threshold of 10 and decrease to 1 for the last layer, but no noise reduction for the residual layer.

Apply.

This takes care of colour mottle while keeping colour everywhere else.
Btw, this isn't my recipe, but I can't remember where I got it from. Probably from Warren's book or Pixinsight resources, http://pixinsight.com.ar/
Wim

AZ EQ6 GT + EQ3 PRO, SW 150P-DS, SW MN190, ZWO ASI174MM-Cool, Pentax K20D (retired),
SW ST80 + ZWO ASI120MM + Lin_guider

Offline pfile

  • PTeam Member
  • PixInsight Jedi Grand Master
  • ********
  • Posts: 4691
    • View Profile
Re: Always splotchy background pollution? Help!
« Reply #3 on: 2019 November 03 07:21:40 »
i first heard about it in the thread i linked above from Alejandro.

Offline wimvb

  • PixInsight Enthusiast
  • **
  • Posts: 91
    • View Profile
    • Wims place
Re: Always splotchy background pollution? Help!
« Reply #4 on: 2019 November 03 14:47:55 »
@DuaneDibbley : Do you dither between exposures? Sveral years ago, Tony Hallas had a talk about colour mottle from dslr's.
Have a look here:
https://www.youtube.com/watch?v=PZoCJBLAYEs

Anyway, this is what I could make of it. The smaller scale blotchiness was removed with MMT, as described. But there was still a lot of red noise left. I made a mask to protect the nebula and reduced the colour saturation in the background a little.
« Last Edit: 2019 November 03 15:38:45 by wimvb »
Wim

AZ EQ6 GT + EQ3 PRO, SW 150P-DS, SW MN190, ZWO ASI174MM-Cool, Pentax K20D (retired),
SW ST80 + ZWO ASI120MM + Lin_guider