Hubble Bubble

[NoelC]

To my shock and surprise the sky cleared on Monday when I was not expecting it.  I rolled out the telescope to take advantage without much preparation, and so still had the narrowband filters fitted in the camera (have to choose which to use well ahead of needing it normally) so headed over to NGC7635 - The Bubble Nebula.

NGC7635 (aka Sharpless 162, Caldwell 11) Emmission Nebula in Cassiopea.  The Bubble Nebula in Hubble Palette.
Taken on Altair 205mm RC at around f5 using an Atic one 6.0
600S sub exposures binned X2, using Sii, Ha, Oiii. 6 exposures each.  Stacked in ASTAP and post processed in the GIMP - uncropped.

[Roberto]

Noel

You have tons of detail in that image - well done!  However is completely green! 
Try to equalise the backgrounds from each of the narrowband masters before combining them to false colour. See how it goes. It's been a while since I've used GIMP but if it allows for masking and overlays using screen functions you can highlight particular areas by increasing the weight of a particular colour using the same master frame as a multiplier.

Roberto

[Carole]

I agree with Roberto.

I tried to make some colour adjustments in Photoshop but could not manage to do anything useful except to find there is a lot more nebulosity lurking in there.

Any chance of posting up the stacks to Dropbox or something so we can have a go at it.

Colour aside that is the best image you have posted so far, I think it is just the processing that needs tweaking.

Carole

[NoelC]

Thank you Roberto and Carole for the advice (sorely needed!).

Roberto; I am struggling with the concept of equalising the backgrounds.  Have tried 'ticking the box' in ASTAP and it doing a background subtraction routine for each channel, but the combined result has purple stars, and white balancing (auto white balance) makes the nebula bright yellow.

Carole; happy to send you some separates; but can you tell me how to balance the colours (in conceptual terms)?  I have been trying to align the R, G & B  peaks in levels (without cropping the black too much) which either produces a cast, or a completely grey image.  I suspect I've miss-understood something critical in this process.

Noel

[Roberto]

Noel

Send me your three master Ha, OIII and SII frames in linear fits format.  I am not familiar with ASTAP so cannot really help there.

Roberto

[Carole]

Hi Noel, I don't use GIMP and can only explain using Photoshop, will this be of any use?

Carole

[Roberto]

GIMP is very similar to Photoshop. It would help him greatly.

[Carole]

I have sent Noel a couple of my PS tutorials.

Carole

[NoelC]

Re: "I have sent Noel a couple of my PS tutorials"
...And very good they are too.  Thoroughly recommended:-
https://www.youtube.com/watch?v=LWqI_T4zAgM

Noel

[Carole]

I have processed your data and sent to you by WeTransfer, and notes on how I did it, I hope that will help.

Carole