IC443 in HOO

[AMcD]

This is the first image I have acquired using my new mount.  The HOO image of IC443 comprises 6 hours of 600sec integrations in OIII and 5 hours of 600 second integrations in Ha.  The stars are RGB with 20 minutes for each channel.  The data was acquired using my QHY268M and Antlia Pro filters with a TS 130 Photoline APO mounted on a Paramount MyT guided using a QHY OAG and ZWO 177MM mini.  The data was acquired under Bortle 5 skies with SGPro and all processing was done in PixInsight.  Constructive criticism always welcome 🙂

 

Edited March 7 by AMcD
Uploaded correct version

[Sunshine]

Beautiful image!

[AMcD]

4 hours ago, Sunshine said:

Beautiful image!

Many thanks for your kind words.  I am pretty pleased with it and with the performance of the MyT so far 

[Fegato]

That's a wonderful IC443 - subtly done and lots of nice detail!  My only comment would be the stars - to my eye the bluer ones seem maybe a bit purple? But then my eyes are not what they were...

[AMcD]

7 hours ago, Fegato said:

That's a wonderful IC443 - subtly done and lots of nice detail!  My only comment would be the stars - to my eye the bluer ones seem maybe a bit purple? But then my eyes are not what they were...

Thanks Fegato, that means a great deal coming from you.  I agree with respect to that stars.  I find processing the stars more challenging than the main event on many occasions.  You would think it would be the other way round. 

I have read about "pre-stretching" them using ArcSin Stretch before applying the final stretch but I have not yet tried that.

[Richard_]

Lovely image, well done! I agree with the CC above regarding the purple-ish stars. What is your process flow for the RGB image? Did it include some form of colour calibration (cc/pcc/spcc)?

Arcsinh stretch is meant to retain some colour hue during stretching, but I sometimes find this gives the cores of stars a pink hue and the stars kinda have a red and blue separation like you see with atmospheric dispersion. See below example from Cloudy Nights.

[AMcD]

2 minutes ago, Richard_ said:

Lovely image, well done! I agree with the CC above regarding the purple-ish stars. What is your process flow for the RGB image? Did it include some form of colour calibration (cc/pcc/spcc)?

Arcsinh stretch is meant to retain some colour hue during stretching, but I sometimes find this gives the cores of stars a pink hue and the stars kinda have a red and blue separation like you see with atmospheric dispersion. See below example from Cloudy Nights.

 

Many thanks Richard.   I combine the RGB in Channel Combination, the apply Background Neutralisation and SPCC before removing the stars using StarXTerminator.  From there I stretch the stars only image.  I have been using GHS but I also find I get quite good results from using Masked Stretch.  I wonder whether inverting the image and then applying SCNR would deal with the purple / magenta cast on the stars.

I have entered a version into the image into the current SGL Narrowband Challenge with HOO stars, but looking at @gorann's collection of entries comprising his narrowband masterpieces I suspect a mug is a forlorn hope 🤣

[Richard_]

59 minutes ago, AMcD said:

Many thanks Richard.   I combine the RGB in Channel Combination, the apply Background Neutralisation and SPCC before removing the stars using StarXTerminator.  From there I stretch the stars only image.  I have been using GHS but I also find I get quite good results from using Masked Stretch.  I wonder whether inverting the image and then applying SCNR would deal with the purple / magenta cast on the stars.

I have entered a version into the image into the current SGL Narrowband Challenge with HOO stars, but looking at @gorann's collection of entries comprising his narrowband masterpieces I suspect a mug is a forlorn hope 🤣

When you combine SHO as a typical Hubble palette, you get magenta stars. There is a script in pixinsight which corrects magenta stars (I think it's called Correct Magenta Stars or words to that effect) which works as you explain. It inverts the image, runs SCNR then inverts the image back to normal. You can apply a star mask to protect the background and you can choose how aggressive the SCNR needs to be. This might work for your stars!

When doing SPCC, you can include background neutralisation at the same time instead of performing as a separate step. Create a small preview window of your image which contains the background, then assign this preview to the "region of interest" box at the bottom of the SPCC dialog and then run. Also, when you complete SPCC your colour calibration charts should hopefully show a linear correlation between the colours. See below screenshot which I pulled from Google. Is this what you see when you run SPCC or do you see something different?

 

[AMcD]

Many thanks @Richard_, I will give it a go.  Yes, that is what I see when I run SPCC.  Many thanks again.