[Solved] Star Color Calibration with Narrowband Data

Dear Wayne @whixson,

Star Color Calibration only really makes sense on broadband RGB data. It can never be performed on narrowband data because Black Body physics needs information of the whole RGB spectrum or at least a large part of that.

The star intensities on those narrowband wavelenghts can deviate big time from the broadband RGB spectrum of the star, because it probably has emission or absorption lines superimposed on the RGB spectrum especially on those narrowband wavelenghts...

So if you want correct star colors you always need to add RGB data. If you only work with narrowband, the star colors will never be properly calibrated.

Mabula

Thanks Mabula. Kind of figured that. Does APP have any tools to integrate RGB stars into a nb image?

wayne

Sure, simply use the RGB Combine Tool to combine Narrowband with BroadBand.

I will soon make a video Tutorial about how you can get RGB stars and Narrowband Nebula like this (this is RGB + SHO data) without even removing stars are using starmasks in the RGB and SHO data:

You can of course reduce/remove the narrowband stars if you want first in the narrowband data before combining with RGB.

Mabula,

A tutorial would be much appreciated! I am also struggling to understand how to replace narrowband stars with RGB stars.

APP has grown so much since I started using it in 2019. Many thanks for all of the speed and functionality improvements in 1.083.3! I especially like the improvements in the star reduction module. That is the one other are where a tutorial would be helpful - for star reduction on only the larger stars. 

Thanks again for all of your hard work!

David

Posted by: @mabula-admin

Sure, simply use the RGB Combine Tool to combine Narrowband with BroadBand.

I will soon make a video Tutorial about how you can get RGB stars and Narrowband Nebula like this (this is RGB + SHO data) without even removing stars are using starmasks in the RGB and SHO data:

You can of course reduce/remove the narrowband stars if you want first in the narrowband data before combining with RGB.

 

That would be a great Tutorial! Looking forward to it!

Jim

Posted by: @mabula-admin

 

I will soon make a video Tutorial about how you can get RGB stars and Narrowband Nebula like this (this is RGB + SHO data) without even removing stars are using starmasks in the RGB and SHO data:

9 months have passed and no sign of tutorial yet...

Can we hope to have this tutorial as Christmas gift? 🤣 

Hi @ippiu,

documentation and video tutorials will get the attention after the 2.0.0 stable release which has all the priority now.

A workflow for RGB + Narrowband  with good RGB stars is not that difficult with APP these days, let me give you a short but good method:

1) Make a RGB composite

2) Star color calibrate that composite

3) make the SHO (or HOO etc) narrowband composite

4) Tune the NarrowBand (NB) composite completely as you would like have it in the final RGB-NB result using the RGB Combine Tool & Selective Color Tool

5) Load both RGB (Star color calibrated) and NB composite into the RGB Combine Tool

6) Keep multipliers fixed for the RGB channels, for instance at default 1.0x

7) Tune the multipliers for the NB composite while keeping them the same, for instance all at 2.0x

There will be a multiplier where the stars still look like star color calibrated stars and where the narrowband signal starts to show nicely !

A next step for improvement would be to perform star removal or star reduction in the SHO composite, making it easier for the RGB stars to show 🙂

Mabula

@mabula-admin 

Thanks Mabula

But by this time, I've been imaging for 2 years apart just "stars" (Uv Ir cut filter) for 30-45 minutes, then separate them with Starnet or StarX, create a star-mask, work on it separately, post process and put stars back onto final nebula or galaxy... 

Posted by: @mabula-admin

Hi @ippiu,

documentation and video tutorials will get the attention after the 2.0.0 stable release which has all the priority now.

A workflow for RGB + Narrowband  with good RGB stars is not that difficult with APP these days, let me give you a short but good method:

1) Make a RGB composite

2) Star color calibrate that composite

3) make the SHO (or HOO etc) narrowband composite

4) Tune the NarrowBand (NB) composite completely as you would like have it in the final RGB-NB result using the RGB Combine Tool & Selective Color Tool

5) Load both RGB (Star color calibrated) and NB composite into the RGB Combine Tool

6) Keep multipliers fixed for the RGB channels, for instance at default 1.0x

7) Tune the multipliers for the NB composite while keeping them the same, for instance all at 2.0x

There will be a multiplier where the stars still look like star color calibrated stars and where the narrowband signal starts to show nicely !

A next step for improvement would be to perform star removal or star reduction in the SHO composite, making it easier for the RGB stars to show 🙂

Mabula

 

Thank you so much Mubula for that step by step explanation!

Hello Mubula, 

I did this over the weekend and it worked great! Thanks again for reply and explanation.

Thank you Mabula!

Ive been using a mono camera (294mm) and have had no luck adding RGB stars to my SHO or HOO composites until I found this thread. 
I’m very excited to finally have this solution just in time the arrival of my new 90mm triplet next week! 

The attached image was taken with my little 60mm doublet last week.

Mark

@markabbott that is a very nice star color calibration you have made. Would you like to state which filters you used, and how long and how many exposures?

best regards John

Thank you John. 

I used Astronomik Deep Sky RBG filters for the stars (45 X 60" for each filter) and combined it with Ha (36 X 300") and Oiii (36 X 300").  The narrowband filters are Astronomik 6nm Ha and 6nm Oiii.  

Total integration was a little over 8 hours.  The Astronomik Deep Sky RGB filters are reasonably priced at $280 for a 1.25" set.

@markabbott Excellent star color and image Mark! Thank you for posting!

Posted by: @markabbott

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Thank you Mabula!

Ive been using a mono camera (294mm) and have had no luck adding RGB stars to my SHO or HOO composites until I found this thread. 
I’m very excited to finally have this solution just in time the arrival of my new 90mm triplet next week! 

The attached image was taken with my little 60mm doublet last week.

Mark

 

Hi Mark @markabbott,

That is a really nice result indeed ! Glad my workflow was of use here  !! I like it, nice star colors and colorful nebulosity 🙂

Cheers,

Mabula