Iris Nebula - star colour with L-Pro

[Matt S]

Martin

Like the Spanish Inquisition, I have another question for you…

Following your Compose module workflow above, should I select the ‘Bi-Color’ preset when entering the Colour module?

And…(in try Python style)…I normally use a Mask to sample the star field and Corte fly set the White Balance: does your workflow essentially make this approach inappropriate?

I’ve already had a crack at reprocessing the Cocoon Nebula (captured using the L-eNhance filter): results are attached. The first of the two images uses the Compose module (following your workflow). I think it looks better than the ‘red blob’ but I need to do something to reduce the blue hue on the stars.

Grateful as ever for any pointers and thanks again.
Matt

[Startrek]

Hi Matt,
Ok firstly the Narrowband colour palette has no scientific documentary value ( unlike Broadband ) and so apart from the standard SHO and HOO blends , folk are able to create ridiculous but amazing “Astro artwork” to provide the Wow factor.
As you are using a OSC camera with L enhance filter ( Ha and Oiii ) you are basically restricted to a Bi colour image as the Sii emission data is missing.
However this doesn’t stop you from experimenting with the various pre set channel blends found in the Matrix of the colour module.
As long as you load your OSC L enhance data set into the 3 slots ( R/Sii , G, Ha , B Oiii ) in Compose and select Select Luminance Colour - L+Synthetic L from R (2xG ) B, R ( GB) (GB) ( Bi Colour from OSC DSLR ) then you have flexibility in creating standard HOO , an alternative SHO or other crazy blends in the Matrix.In any case Compose will create a Synthetic Luminance L from your data set to ensure detail is not compromised when creating these NB palettes.

Important - Most emission nebula located in HII regions of the Milky Way emit very strong Ha signals , weaker Oiii signals and even weaker Sii signal wavelengths. So because Ha is so strong , the Reds and Pinkish Red colours are the overwhelming dominant colour followed by Oiii signals ( Greens and Blues and finally Sii which is also in the red spectrum.
Don’t be surprised you will find it difficult to extract the Oiii signal ( greens and blues ) from certain emission nebula as the signal is so weak.This where Mono and dedicated filters shine as you are receiving 100% available signal ( no Bayer Matrix )
Most of the larger Emission nebula usually have stronger Oiii signals so creating a really good Bi Colour Narrowband image will be easier.

When you first open the Colour module you can use the Bi Colour preset button at the top or alternatively use the Matrix to navigate to the first HOO Duoband blend.
On certain emission nebula , HOO will create an overall dominate Red / Pink colour with signs of green / blue in regions.
You can also try the SHO preset ( even though you have no Sii data ) or alternatively use the Matrix. I find the 3rd SHO option in the Matrix works well.
Startools colour module opens up and endless choice of Narrowband colour blends through preset mapping via the Matrix.

Important- in most cases you will have to back off or reduce the Green colour bias slider to balance the colour and bring out the best in a Bi Colour or Tri colour image.

Also experiment with Style and Emulation method in Colour Module together with adjustments in Saturation etc….

Now getting back to a few questions -

White balance stars ? I personally don’t use this feature as it made no difference either way.

Green halos around Stars
This is typical for an HOO image
With an SHO image Star halos tend to be purple , magenta or burgundy colour.

To reduce this affect use the colour correction tools I previously mentioned.

Highlight in Colour module ( bump up to 9 pixel strength)

Shrink module ( Colour taming )
Star Colour Correction using Shrink Module
Create a good Star Mask and ensure all star cores and halos that require colour correction ( including diffraction spikes ) are sampled or green. Grow mask as required

Open Shrink
Adjust iterations to 0
Change Mode to Tighten
Color Taming increase to between 4 and 10 pixels as required.
Note: Be careful not to increase Color Taming too much as this can cause Star cores to bleach out colour or “white out”. Start off with 2 pixels , then 4 pixels and so on until Star colour is reasonably uniform in the core and halo area.
Halo Extend increase to 1 or 2 pixels
Un glow Kernel leave off

Abnormal Stars core and halo colour ( and diffraction spikes ) should morph or blend into a uniform colour closest to adjoining colour of star core.

Filter module ( Fringe killer )
Star Colour Correction using Filter
The Filter module can help colour correct star halos.
Obviously Filter is used after Colour Module
Filter mode use Fringe Killer
Sampling Method use 3x3
Filter Width try 1 to 5
Mask Fuzz 1.0 pixel to 4.0 pixels
Create a good Star mask ( including touching up diffraction spikes if using a Newtonian)
Select mode as Fringe Killer
Sampling use 3x3
Click on Star Halo to change colour closer to Star core. Each click will slowly change colour as required.
Adjust parameters as required to achieve best outcome
Press Save once completed


Maybe your next investment could be a better OSC narrowband filter like the Antlia ALPT Golden 5nm or L Ultimate 3nm where you can really narrow in on those weaker Oiii signals to produce a better cleaner Narrowband Bi colour image. I’ve used quite a few OSC dualband filters over the years and the Antlia ALPT 5nm was in my opinion the best for my F5 Newts , minimal halo on stars and excellent performance in regards to signal.


Hope I didn’t miss anything

Good luck

Oh and your image of the Cocoon using Compose does look much better.
Well done !

Clear skies
Martin