Correcting a strong Blue/Violet Cast

That might be a good idea (to share the files), the star colour graph looks really weird and there seems to be some over representation of green in the data.

Hi Mike @mestutters & Vincent @vincent-mod ,

Yes, I see the issue with the data. My first guess would be that the HaLRGB composite actually is the problem. If I look at the histogram in the Remove Ligh Pollution stage. Green versus Red+Blue is rather unbalanced and this most likely leading to the issue in star color calibration.

The star color calibration Black Body models need broadband data to work well, but you have supplied broadband with R,G,B data. So I suspect the issue is to be found in how the Ha data is actually added to the composite.

Regarding HSL selective color: it's needed for final small tweaks mostly. We first should get a better result at the star color calibration stage I feel... before continuing with processing.

I would be happy to have a look at the data, please send the integrations per channel to me. I will then have a look to find a possible issue and otherwise suggest a better workflow 😉

You can send the data to support@astropixelprocessor.com using wetransfer.com or dropbox 😉

And I agree, the data itself looks promising, the nebulosity looks rich in signal.

Kind regards,

Mabula

Hi Mike @mestutters ,

Thank you for sending me the data.

When I load the R,G,B channels into the RGB Combine tool, I immediately get an odd result I think.

This is just with R,G,B multipliers at 1.

The magenta cast comes from Red and Blue dominating the green channel. The nebulosity is magenta everywhere which is odd.

If we look at the Red, Green and Blue channels:

We can see why, the nebulosity and Cresent is visible in Red AND Blue, not in Green.

I would almost think that somehow red and blue data was mixed in the final red and blue integrations.

The brightest stars in the red channel are also the brightest stars in the blue channel it seems and there is a big difference in quality as well.

Perhaps to investigate further, can you share some individual red, green and blue frames ? Maybe that will give a better understanding of what is happening here 😉

Kind regards,

Mabula

Hi Mabula,
Thank you for taking a look at my earlier attempts at Crescent nebula image and for your suggestion as to what might be wrong. I took a close look at my all my subs and found that amongst my Blue frames I had several (c30% of total) that looked as if they had actually been recorded through Green filter rather than Blue. Not sure how that happened but an operator error I guess!
Anyway I managed to capture a few extra Blue subs the other evening to replace the faulty ones and have had another shot at processing. The result now looks rather better but on the B-G vs G-R chart the star profiles seem to have a negative slope. I think that this cannot be right although on other images I have done I generally have to set the slope value to near the lowest settings available.
I hope I have not made another silly mistake but I would much appreciate your view as to where I might still be going wrong.
I will very shortly forward my latest integration frames and examples of my HaLRGB frames.
Best Regards
Mike
PS : I've just enjoyed viewing your AstroImaging Channel talk and am looking forward to seeing the further improvements you have planned for APP. Hope you very much enjoy your holiday too.

Hi Mabula/Vincent,

Please consider this problem closed.  I managed to capture a few more subs on this target and was then able to carefully compare what I had with the new results.   After weeding out a few more older subs that looked suspisiously as if they too were incorrectly labelled  I am now getting a result in CSC that looks about right. 

Thanks for your time and patience

Mike

Was just about trying to be of assistance. 🙂 Glad it worked out ok!