NGC6188/6193/6164 etc

[DJT (David)]

I have got into a bad habit of revisiting last years images but this time with the FS60 as I am enjoying setting those objects in the context of their wider surrounds.

Full image
NGC6188 and 6193

Having trouble with the colour in this though. 80% of the ones you see on the web have a distinct Maroon hue to them. I cant for the life of me get close to that. Hey ho.

RGB only, shot using a Canon 60Da with a CLS filter, 360 sec subs at ISO400, around 6 hours of integration in all.

Thanks for looking

[multiweb (Marc)]

Top shot David. Recently imaged this one in RGB too. I felt your color balance was a little off towards the red. I did a quick tweak on the central part. Couldn't get all the blues back as there area little clipped but you probably can fix that in the RAW FIT.

[Ross G]

Good looking photo David.

Sharp and the colours look ok to me....although, like you, getting the colours "right" is always my biggest hurdle!

Ross.

[DJT (David)]

Originally Posted by multiweb

Top shot David. Recently imaged this one in RGB too. I felt your color balance was a little off towards the red. I did a quick tweak on the central part. Couldn't get all the blues back as there area little clipped but you probably can fix that in the RAW FIT.

Thanks Marc. Can I ask what the tweak was? There appear to be multiple ways to play with the colour on PS. Looks like maybe pulling down on a curve on the red channel? Will have a look at what you have done tonight and see if I can replicate it.

Originally Posted by Ross G

Good looking photo David.

Sharp and the colours look ok to me....although, like you, getting the colours "right" is always my biggest hurdle!

Ross.

Thanks Ross. An having a bit of an issue with field flatness even though I have a dedciated TAK flattner though I am hoping a replacement t-ring has fixed that. The original had a bit of a wobble going on. Initial subs seem better but even so, I think I am starting to get the hang of controlling the stars when processing ..now if I can just sort out the colour..

[multiweb (Marc)]

Originally Posted by DJT

Thanks Marc. Can I ask what the tweak was? There appear to be multiple ways to play with the colour on PS. Looks like maybe pulling down on a curve on the red channel? Will have a look at what you have done tonight and see if I can replicate it.

Sure. All I did was push the greens and blues then offset them back. Bit of saturation tweak. Are you using CCD Stack originally? If you are familiar with pixel maths here's some notes I did for myself that may work for you. The ratios are for an OSC (my QHY8) but you get the gist of it:

1_ Stack all channels separately.
2_ Load color channels then register to best FWHM (usually green)
3_ Deconvolve green 30 iterations. Save PSF.
4_ Deconvolve Red & Blue loading Green PSF.
5_ Pixel math to largest int mode picking black starry background (not dust if possible)
6_ stretch channels to look good then save as 32bit float (!!ALWAYS - NOT 16Bit!!)
7_ Load color channels then color combine at 1, 1.22, 1.77 -> create.
8_ * update: do not Select black area to set background with 'Desaturate background' selected -> this creates posterization in the blues and reds then combing in PS. Instead, stretch colors then offset until histogram is equalized.
9_ Tweak DDP to red so no clipping then apply as Red is predominant.
10_ Adjust color then increase blue and green factor to get yellow milkyway sandy stars + blues

I anything's unclear just ask.

[DJT (David)]

'Thanks for the info Marc
I used nebulosity 3 for callibration and stacking for this image, first time use. As I am using a DSLR I dont think i can stack as separate channels? Looks like I do need to look at pixel maths though all good learning fun. Happen to have a copy of "the handbook of astronomical image processing" on my lap and I aint reached that chapter yet!

Will chew through your workflow though. On the colour combine I assume the ratio 1:1.22:1.77 is R as 1, G as 1.22 and B as 1.77?

Thanks again.

[multiweb (Marc)]

Originally Posted by DJT

'Thanks for the info Marc
I used nebulosity 3 for callibration and stacking for this image, first time use. As I am using a DSLR I dont think i can stack as separate channels?

Yes you can debayer RAW DSLR files to separate RGB channels. MAXIM does it. I think PixInsight will also read the files. Or try FITS liberator, free download from the NASA website maybe.

Originally Posted by DJT

Looks like I do need to look at pixel maths though all good learning fun. Happen to have a copy of "the handbook of astronomical image processing" on my lap and I aint reached that chapter yet!

Will chew through your workflow though. On the colour combine I assume the ratio 1:1.22:1.77 is R as 1, G as 1.22 and B as 1.77?

All worth your learning. Yes RGB in that order. For a DSLR being more sensitive in the blues and greens I suspect you'll need to push the reds.