Author Topic: PCC Narrowband Filter settings for specific Tri-band filter  (Read 1384 times)

Offline JST200

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Hi,

If the specification for a specific Tri-band filter says:

    The Tri-Band combines Ha into a red zone, and H-beta + Oiii into a green/blue zone.
    1st band, CWL495nm FWHM35nm
    2nd band, CWL 654nm FWHM 12nm

What should the PCC process Narrowband Filter settings be set to?

Thanks for any help!

Cheers, Jim

Offline John_Gill

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Re: PCC Narrowband Filter settings for specific Tri-band filter
« Reply #1 on: 2020 February 07 04:53:43 »
Hi,

I think that PCC only needs to know if the image is in Narrowband which is Ha, Sii or Oiii or Broadband which is LRGB or OSC

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Offline Juan Conejero

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Re: PCC Narrowband Filter settings for specific Tri-band filter
« Reply #2 on: 2020 February 07 07:22:58 »
Hi Jim,

In narrowband mode, PCC needs to know the parameters of the filters used to acquire the red, green and blue channels of the image. For each filter, the central wavelength and bandwidth must be specified, both in nanometers.

From the data you have provided, for this filter set you should specify the following parameters:

Red channel: wavelength=654 bandwidth=12
Green and blue channels: wavelength=495 bandwidth=35
Juan Conejero
PixInsight Development Team
http://pixinsight.com/

Offline JST200

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Re: PCC Narrowband Filter settings for specific Tri-band filter
« Reply #3 on: 2020 February 07 09:48:38 »
Brilliant! Thanks, Juan.  :)

I was going round in circles getting my head around which was assigned to which.

It will be interesting to see how much difference it makes.

Another question if I may... Once I have an integrated OSC image, should I be doing a Channel Extract, Linear Fit, Channel Combine, before running PCC, as I have been doing? Or is it not worth it and I just need to run PCC on the integrated OSC?

Thanks, Jim

Offline Juan Conejero

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Re: PCC Narrowband Filter settings for specific Tri-band filter
« Reply #4 on: 2020 February 07 10:07:18 »
Hi Jim,

Quote
Once I have an integrated OSC image, should I be doing a Channel Extract, Linear Fit, Channel Combine, before running PCC

Not at all. That does not make any sense. Just apply PCC directly to the linear RGB image, selecting a good region of interest for background neutralization. See this post for a good example.

Out of curiosity, where does the idea of applying LinearFit to individual color channels come from?
Juan Conejero
PixInsight Development Team
http://pixinsight.com/

Offline JST200

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Re: PCC Narrowband Filter settings for specific Tri-band filter
« Reply #5 on: 2020 February 08 05:46:24 »
Hi Juan,

Thanks for the correction. :)

Apologies for not replying sooner, but I have been thinking about your question and how to reply.

In short... the idea came from my lack of knowledge, skill and understanding of how best to use PixInsight. I have been trying to create the basis of an end to end process. Whilst doing so I come across snippets of ideas which I try and if they seem to improve the end result I keep in the process. This was one of the snippets.

In long... because of my Bortle 6 location I have started using a Tri_band filter, which works really well. However, with my current process, I end up with with heavily red biased images (at least I think they are). Others I know, who have similar if not the same equipment configuration, seem to be able to produce images with a better colour balance.

At this point there are two threads.

Firstly; I was researching whether I am better using a linked or unlinked RGB channel Histogram Stretch after running PCC. It did seem that I got a better end result using a linked stretch. During the research I came across some posts that suggested the best way to balance the channels was to extract the RGB channels, use LinerarFit and then recombine them. The best time to do so was whilst the data was still linear and I assumed it would be better before running PCC.

Secondly; at least part of the reason that others appear to get a better colour balance seems to be that they use Astro Pixel Processor. APP has support for the tri-band filters built in to it's processing capability. As I understand it, it extracts the RGB channels (another link into the research above) and then recombines them using the tri-band filter attributes I noted in my previous post (I can provide a link to a video where this approach is demonstrated, if required). Again I was researching how to do something similar using PixInsight. Somewhere during that investigation I became aware of the Narrowband PCC option and thought that might provide a way forward for me.

Does that help provide an answer. Or (more likely) does it just show up my lack of understanding and raise even more questions? :embarassed:

I have a question of my own, if I may... I have a series of Icons in my workspace that help provide me with a process flow. The cover a basic full end to end process. I would love it if someone would look at my process flow and provide some honest feedback on where it's OK and where it doesn't make sense. What's the best way for me to get that sort of help? Should I open a specific post?

Anyway, again thanks for you help.

Cheers, Jim