Star Color Calibrat...
 
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9 July 2020 - APP 1.082 has been released which contains one important bug fix. 1.082 has full Fujifilm RAF support, so that includes SuperCCD & X-Trans camera's 🙂 !

9 July 2020 - New and updated video tutorial using APP 1.081: Complete LRGB Tutorial of NGC292, The Small Magellanic Cloud by Christian Sasse (iTelescope.net) and Mabula Haverkamp

2019 September: Astro Pixel Processor and iTelescope.net celebrate a new Partnership!

Star Color Calibration Issue  

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 SdA
(@sda)
White Dwarf Customer
Joined: 3 years ago
Posts: 10
May 28, 2020 16:16  

The mean differences between the channels R,G,B are from 2.53 to 3.02, too low. So RGB il almost white. The mean difference between Ha and the other channels is ~ 11.12, 4 times more. 

 


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(@hyperion)
Main Sequence Star Customer
Joined: 1 year ago
Posts: 33
May 28, 2020 16:24  

@sda

The rgb data is split channels from Broadband filter With osc camera zwo 294 and the filter is L pro. The Ha data is extract from L enhance narrowband filter ... this is the workflow that I following https://www.astropixelprocessor.com/community/tutorials-workflows/combining-r-g-b-with-ha-oiii-data-using-an-optolong-l-enhance-filter/


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(@vincent-mod)
Quasar Admin
Joined: 3 years ago
Posts: 1913
May 29, 2020 10:15  

Yes that could be one of the issues. You can always lower the amount of Ha you use for instance. Mixing it 50-50.

I'll have a look today.


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(@hyperion)
Main Sequence Star Customer
Joined: 1 year ago
Posts: 33
May 29, 2020 10:16  

@vincent-mod

ok Vincent... I will waiting your processing... 

Thanks again ...


(@vincent-mod)
Quasar Admin
Joined: 3 years ago
Posts: 1913
May 29, 2020 14:32  

So here's what I got. I selected stars on the left hand side and another big box underneath the galaxy. It seems that the filters do change the broadband data a bit, so I tweaked the slopes a little bit to have the line go through the population a bit better (that's the white line in the correction graphs). I also made a comparison with 50% Ha into the red and 33% Ha into the red. Before I combined all panels, I first did light pollution correction to have a nice background, all similar to each other.

This is right after combination with 50% Ha;

HaRGB

This is with color correction and a tweaked slope of the line. I also lowered both Magenta - Green slider to about -0.05 to remove a bit of green cast;

HaRGB colorcorrection

Next up, 33% Ha into red;

HaRGB collorcorrection 33Ha

And with tweaked slopes;

HaRGB colorcorrection Ha33 tweaked

Saturation was upped a bit to 0.19. Is this more to your liking? It does seem the colors could be more pronounced, what was the total integration time?


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(@hyperion)
Main Sequence Star Customer
Joined: 1 year ago
Posts: 33
May 29, 2020 14:40  

@vincent-mod

Hello Vincent ...

For sure is better than my processing ...

the total time is about 10 hours ... 7 rgb and 3 Ha

 


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(@hyperion)
Main Sequence Star Customer
Joined: 1 year ago
Posts: 33
May 29, 2020 14:43  

@vincent-mod

I think that before star color calibration you still get better result ...

What you think  ?


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(@vincent-mod)
Quasar Admin
Joined: 3 years ago
Posts: 1913
May 29, 2020 14:56  

No, personally I don't think so. That first image looks very dull, color wise. So there seems to be an offset, created probably by the filters.


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(@hyperion)
Main Sequence Star Customer
Joined: 1 year ago
Posts: 33
May 29, 2020 14:58  

@vincent-mod

I can’t have good view from screenshots ... plz when you finish upload it in server to check it ...

 


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(@vincent-mod)
Quasar Admin
Joined: 3 years ago
Posts: 1913
May 29, 2020 15:27  

Ofcourse, I uploaded the 33% Ha into Red final stretch in your directory on the server. The file is called "combine-RGB-image-33Ha-cbg-St.fits"

 


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(@hyperion)
Main Sequence Star Customer
Joined: 1 year ago
Posts: 33
May 29, 2020 15:29  

@vincent-mod

great so you went until star color calibration step right ?


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(@vincent-mod)
Quasar Admin
Joined: 3 years ago
Posts: 1913
May 29, 2020 15:36  

So to recap;

  1. Loaded all integrations and performed light pollution correction on each of them.
  2. Combined them in HaRGB, 33% Ha into red.
  3. Did another light pollution correction.
  4. Color calibration, large boxes around the galaxy and tweaking of the slopes to better match the star population.
  5. I removed some green bij moving the sliders (both of them) from green towards magenta with a value of -0.05.
  6. I added saturation, Sat. 0.19.
  7. Saved the stretch and uploaded it to the server for you.

Just so you have the details of this stretch. 😉


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(@hyperion)
Main Sequence Star Customer
Joined: 1 year ago
Posts: 33
May 29, 2020 15:41  

@vincent-mod
Thats great Vincent...

really I appreciate it ... 

I will continue in hsl step ...

clear skies ...


(@mabula-admin)
Quasar Admin
Joined: 3 years ago
Posts: 2451
May 31, 2020 14:56  
Posted by: @hyperion

I try to process my data from m51.

My files  are R G B and HA from OSC 

Everything going normal before Star Color Calibration after this my data taking a reddish color and i cant get over it ...

 This is Before star Color

Be4 Start Color  Calibration

And this is after

 

After Star Color Calibration

Any Help will be appreciate  it ... 

If someone want i can upload my data to check it ...

Many thanks.

 

Dear Stratos @hyperion , @vincent-mod, @astrogee, @sda ,

Thank you Stratos for sharing your data with us 😉 I have had a go myself since I am actually working to improve HaRGB and LHaRGB composites for a future APP release.

The workflow to do star color calibration on a HaRGB (or a LHaRGB) is not recommended, in fact it is physically a wrong step. You need to do star color calibration on broadband data. If you add narrowband data in the mix and then try to perform star color calibration on a broadband+narrowband composite, it would be mere coincidence if the colors look good...

Star color calibration needs broadband data to make sense of the star color physics. Adding narrowband data in there will cause the R/G B/G ratio's of the stars in your data to be polluted by the narrowband emissions. Those narroband emissions don't follow the physics at all that we use for star color calibration.

So how to do this properly then?

1) create a RGB (or LRGB compositie), in this case I used formula RGB 2 in the RGB Combine tool

2) perform Remove Light Pollution and Background Calibration on the RGB composite ( ! if you perform Remove Light Pollution, you automatically perform Background Calibration, there is no need to do it again after Remove Light Pollution)

3) Perform Star Color Calibration on this RGB composite that is corrected for light pollution and is background calibrated:

RGB2 formula LPC CBG SCC

4) We know open the RGB Combine tool and will add the H-alpha layer. Now, this next 2 steps are essential to preserve the RGB Star Color Calibrated colors in your composite:

  1. set normalize to none in the RGB Combine tool.
  2. Load the RGB star color calibrated result into the tool with the RGB 1 formula

These 2 steps will preserve the colors of the star color calibration 🙂 !

5) Add the H-alpha layer in the RGB Combine tool.

RGB2 formula LPC CBG SCC add Ha layer

6) To preserve the colors and luminance of your star color calibrated result, set the luminance for the composite so that it is preserved. Normally you want Red to contribute for roughly 20%, Green for 70% and Blue for 10%.

7) And slightly add H-alpha to red, I added it for 23% to Red as can be seen in the below screenshot. Now to maintain the star colors, you need to gently adjust the multipliers for the R,G,B channels as can be seen as well. Red 1,15, Green 1,17, Blue 1,20. These factors do depend on the data, you need to do this carefully. Try to get the same colors as the star color calibrated result off course 😉

RGB2 formula LPC CBG SCC add Ha layer finished

I am working to make this more automatic and easier for the user off course, but this is a proper workflow in which you can get good star colors with narrowband included to enhance the active regions in this case of M51 😉

This show the star color calibration result next to the final HaRGB composite: we see that star colors are still good and we also see much more enhanced active regions in M51 from the H-alpha data, top is the RGB composite after star color calibration, below is the finals HaRGB composite with the same star colors 🙂 :

RGB versus HaRGB star colors maintained

Let me know if this is clear and/or if you have any questions about this workflow 😉

Crop of the field of view of the final HaRGB:

M51 HaRGB Stratos Mabula crop

Cheers,

Mabula

 

This post was modified 1 month ago by Mabula Haverkamp - Admin

(@vincent-mod)
Quasar Admin
Joined: 3 years ago
Posts: 1913
May 31, 2020 15:13  

Owkee, well, I'm learning something as well there. 😉 I was assuming that, since there is broadband data, it would still work. But makes sense indeed, that's why I needed to fiddle around with the slopes apparently.


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(@hyperion)
Main Sequence Star Customer
Joined: 1 year ago
Posts: 33
May 31, 2020 16:08  

First of all I must thank you for this great explained workflow and saw us where was our mistake ...

This is great because we know now to process narrowband and broadband data ... 
The last years color cameras with narrowband and broadband filters are so popular and seems like the came to stay ... 

This will be great tutorial for all people that use this kind of equipment...

I will try it this tutorial and I let you know how went ...

ps you can upload your version in server that can I take it to compare with mine ?

Thanks again

Stratos S.

clear skies...


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 SdA
(@sda)
White Dwarf Customer
Joined: 3 years ago
Posts: 10
May 31, 2020 17:19  

Great Mabula, perfect !

Μάστορας ο Mabula !


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(@hyperion)
Main Sequence Star Customer
Joined: 1 year ago
Posts: 33
May 31, 2020 17:31  

@sda

we learn a great tutorial here ...

Πολύ καλή επεξεργασία ... είναι μάστορας τέλος ...


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(@mabula-admin)
Quasar Admin
Joined: 3 years ago
Posts: 2451
May 31, 2020 20:21  

Hi Stratos @hyperion & @sda

You can download my results here for comparison:

https://ariesprodstor.astropixelprocessor.com:5001/sharing/ln6VU6x8C

Cheers,

Mabula


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(@hyperion)
Main Sequence Star Customer
Joined: 1 year ago
Posts: 33
May 31, 2020 20:24  

@mabula-admin

Thank you so much Mabula !!! 
really I appreciate it... 

This workflow will be so helpful for all 

Narrowband and broadband users ...

 


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