Caldwell 27

[NoelC]

A first shot at assembling an LRGB image in Photoshop (following Carole's excellent workshop).

I took the luminance 11th July, but didn't get to see it again until 10th October 2018 when I took the RGB.
Composed it in APP, which has a really excellent registration routine (you just throw them all in and tell it to register) but unfortunately due to the time difference the bottom corner came off the luminance!  Have some more data to try again.

Image date, time and location:   11/7/2018 & 10/10/2018 (North West Kent, UK)
Telescope aperture and focal ratio:   Altair Astro RC 200mm F8 on Skywatcher EQ6-M Pro
Camera and filters used:   Atik One 6 @ -20°C (0.6"/pix. L, 1.2"/pix. RGB)
Processing applied:   Pre-processed and registered in APP, Post Processed in PS CS2
Subs:L 14X300S@1x1, R 10X300s@2x2, G 9X300s@2x2, B 6X300s@2x2 (cloud came in)

[ApophisAstros]

Great image Noel, really like that, lovely variances in star colour.
Roger

[Carole]

Also known as the Crescent Nebula and NGC6888

You've done a great job at assembling the colours Noel, and a success to your first combination of LRGB, but if you take a look in PS, in levels you will find you have clipped the black point and lost data because of it.  Great star colour and guiding.

i.e. the histogram is right up against the left hand side, there should be space between the edge of the box and the histogram.

Did you assemble the colours before processing, or process them individually before combining?  It could be at any of the stages that this happened, but I suspect it was with the combined stage that this happened.

Carole

[NoelC]

Thanks Roger - me too, is it slightly green?? - can't really tell.
Thanks Carole - assembled in photoshop (as APP didn't like the different resolutions; can't think why as it registered them all OK) but the L was shot at 1X, the RGB at 2X. It was the colour balancing that I couldn't get, until you showed how.  Background was very noisy so tried to make it blacker.

[Carole]

Background was very noisy so tried to make it blacker.

That might be the cause.  What method did you use the darken the background?

Carole

[NoelC]

Carole - Errr, just tinkered with the sliders until it went darker (is that the wrong answer?).
Here's another attempt using Ha and OIII.  Put the OIII into the blue and green channels, but can't really see the effect of it.

I have to say I'm underwelmed with the detail I can tease out of the data.

[Carole]

Regarding the LRGB version:

Errr, just tinkered with the sliders until it went darker (is that the wrong answer?).

could be Lol.  If using Levels, never slide the black slider any further than the histogram, don't even touch the histogram. 

The trouble is you lose nebulosity which then can't be retrieved.  I suggest you go back to just before you did that darkening and try again.

Re: Ha and Oiii version,
What length subs and did you try to get the background too dark again?

Carole

[NoelC]

Carole
Ha OIII version:-
L 14X300S@1x1, Ha 9X900S@1x1, OIII 9x600s@2x2
Same luminance data for both images, adding luminance in PS as a layer. The histogram goes a bit awry when trying to balance the colours.  Do you only adjust the grey level? By the time I can see any of the detail the background is all grey.  Will go and watch the videos again.
Noel

[Carole]

I adjust both the black and the grey sliders but only bring them close up to the histogram, never on it.

The sky is not black - though I know some people like to hide the noise, but not at the expense of permanently losing the nebulosity.

Carole

[NoelC]

Carole

This is just HOO (ditched the L).
Here's my last attempt, taking on board some of what you said (left background noise in).
There are all sorts of problems with this (noise, dust and OIII) but at least the nebula is starting to show more.
Took my previous stacked outputs from APP and re-saved them -
Not sure what I was doing wrong but I suspect that AA5 was compressing the files to 8 bit when converting from FITS to TIF (APP gives you the choice).  I can't see what's wrong with my OIII (except that it's out of focus or the guiding went wonky) - stripped the camera to get to the filters and confirmed I have OIII in the right slot???  Got hot pixels all over the OIII - shuvved it through the scratch filter to remove most, there is a hole in the centre of the nebula in OIII (is this a stacking artifact or have I discovered a new planet?).
This isn't easy is it?

[doug]

This is Carole replying on Doug's computer. 

Wow Noel, what a vast improvement.  Great work.  I know there is some noise and this can only be sorted by lots and lots of data.  If you want to darken the sky I'll show you how to do it without clipping data.

Well done.

Can I suggest you try to put the star colour back.  It's probably too late for this image now as you would have to go back to the start, unless you can copy in the stars from, your first image.  Again I might need to show you how.

Carole

[MarkS]

Wow!  The difference is astonishing!

That is looking really good now and completely different to the first attempt.  It's amazing how much data was hidden in that image waiting to be pulled out.

You ought to be really pleased with that.

Mark

[NoelC]

Thanks Doug (all advice gratefully received).
Thanks Mark

[Carole]

Thanks Doug (all advice gratefully received).

Lol, that was me (as explained in the post), using Doug's computer.  Ha ha.

Carole

[RobertM]

You've come on leaps and bounds since you started Noel !  That really is a great image and as Mark has already said you ought to be really pleased with that one.  Perhaps it needs a bit more exposure time but then what image doesn't !

Of course now you can do that then we'll be expecting more from you in the future 

Robert