Yet another M13

[DaveS]

'Tis the season...

Going to see a few more of these over next weeks I should think, but here's mine so far.

TS Photoline 130 f/7 Triplet, TS 2.5" flattener, ZWO ASI1600 at Max DR, ZWO RGB filters, 75 min of each in 5 min subs.

Stacked in AstroArt 5 using Sigma Add, Bias. Dark and Flat applied. RGB Trichromy in AA5 then DDP.

This is a slight crop for framing.

I think it could do with a saturation boost, but I was worried about making the star at the top too red.

As always, C&C welcome. Thanks for looking.

[Allinthehead]

Nice one Dave. 

[Tigaroo]

What a beauty! 

[DaveS]

Thanks !

I had another look and gave it a slight saturation boost from 50% to 65% in AA5 with background held back

I think it's a bit better without being OTT.

I'll try to get more data on the next clear night.

 

Edit:

I've just realised  / remembered that when I capture in Maxim and process in AstroArt I need to do a vertical flip which I haven't done here. I'll leave it as is and only do a flip the next time I have anything useful to add.

[gnomus]

It is pretty nice as is.  Could it maybe have a touch of the greens?  It could be my monitor.  But if I'm right it could help star colour a bit.

[DaveS]

16 minutes ago, gnomus said:

It is pretty nice as is.  Could it maybe have a touch of the greens?  It could be my monitor.  But if I'm right it could help star colour a bit.

Thanks Gnomus.

I'll have another look. Not having PI or PS I can't use the usual green reduction tools. I'll see what I can do in AA5 with its colour controls.

Time to stump up for PI?

[AKB]

24 minutes ago, DaveS said:

Not having PI or PS I can't use the usual green reduction tools.

The SCNR process, described here...

https://www.pixinsight.com/doc/legacy/LE/21_noise_reduction/scnr/scnr.html

is trivial to implement if you have something that does low-level pixel-math sort of things.

It (Average Neutral Protection) simply replaces the green channel G with G' defined by:

m = 0.5×(R + B)
G' = Min( G, m )

It's very effective.

Edit: I took the JPG and ran it through the process (using MATLAB.)  It does show a reduction of about 5 levels in green across most of the image, although not sure if you will see it in this post.

[DaveS]

Thanks AKB, I'll have a propper look a bit later as I'll need to be fully awake and up to speed.

[gnomus]

Hi

I hope you don't mind, but I downloaded your JPEG and had a look.  Now bear in mind that there is not much that can be done with an 8-bit JPEG - any processing is likely going to lead to harsh results and artefacts.  Anyway, I did an STF stretch in PI just to check if I was right about the green.  Here is a screenshot:

Note also that you have some red in the corners.  In my view your black point was also too low.  In Photoshop, the 'eyedropper' tool, hovered over an area of your background sky, showed:

The R is at 1, the G at 6 (confirming the excess of green) and the B is at 0.  For comparison, Olly Penrice usually suggests that the sky should be around 23,23,23 (and who am I to argue with him). 

The first step then, was removing the gradient using DBE in PixInsight.  (This was a JPEG so I didn't want to waste too much time - this is a real quickie - you will do better with the proper FITS or TIFF file).  

DBE removed much of the green and some of the red.  If it were my image and I was working in 16 bits, I might have run a second iteration of DBE.  I then run one iteration of SCNR Green at full strength.  I then stretched the image a small amount.  Because it was 8 bit, a bigger stretch just resulted in mayhem.  I ended up getting the RGB values around the 16,16,16 mark (as measure via the PS eyedropper).  

I think the star colour is a bit better in the final version, but (I know I'm sounding like a broken record) this was an 8-bit JPG I was working on.  You can still see some red in the corners.  This took around 5 mins total.  You should easily be able to do better with the 16-bit image and a bit more patience.

I went back and forth on purchasing PI.  My thinking was: I have spent a small fortune on kit.  I am spending hours of my time gathering data.  I am going to spend hours of my time processing that data.  I may as well get the tools I need to do that job properly.  Whilst typing this I was reminded that when I was a child I would sometimes see my father trying to use cross-head screws with a flat-bladed screwdriver because he didn't have a cross-head screwdriver.  Sometimes it worked - sometimes it mangled the screwhead.  Jings, I am becoming avucular in my old age!!!! 

 

 

 

[AKB]

3 minutes ago, gnomus said:

I am becoming avuncular in my old age!!!! 

I love that word... you just don't see it enough these days!

[DaveS]

Many thanks AKB and Gnomus, that's exactly the feedback I'd been hoping for.

Looks like I may have to stump up for PI after all, I'd been considering it for a while now, like you I was going back and forth, should I, shouldn't I. I was going to say dithering, but I didn't dither this image.

I normally post PNGs, but the full PNG is 50 meg, which is a bit much for an upload, hence the JPEG.

Meanwhile I'll go back into AstroArt and see what I can do,

[gnomus]

You can download and try PI.  I found the interface confusing and I dsiliked it for a long time.  I was also a little put off by the puritanical attitudes of some users - I don't see the difference between creating (an often complex) mask in PI and then running a process, and creating a mask in Photoshop and doing an adjustment.  Yet the latter often is decried by the PI-Purist as 'painting'.  You will find lots (and I mean lots) of processes in PI and you will struggle to understand what 9/10 of them do.  Nevertheless, after spending some time persisiting with it, it will (I promise you) start to get a bit easier.  And things like DBE and SCNR are wonderful and easy to use.  It also has quite a good PreProcessing script that will calibrate and stack your images for you.  

 

[gnomus]

53 minutes ago, AKB said:

I love that word... you just don't see it enough these days!

Very droll.

[AKB]

10 minutes ago, gnomus said:

I found the interface confusing and I dsiliked it for a long time...

...You will find lots (and I mean lots) of processes in PI and you will struggle to understand what 9/10 of them do.

...these are some the reasons why I haven't got PI either. 

I really, really, want to understand what and why I'm doing to my image, so I mostly use my own processing.  This is not because I think it will be better than 'industry-standard' approaches – it probably isn't – but AFAIK the two main reasons for PI are DBE and SCNR, and these are quite easy to implement, and I happen know MATLAB rather well.

[DaveS]

Well I've had another go, but not sure it's any better.

I brought each stack into AA and ran Adaptive Subtract gradient removal on each before RGB Trichromy. Checked WB then pulled green down from, 1.0 to 0.95, which seemed to work OK

Next did a DDP to hold back the very bright core while also trying to hold onto the faint galaxies, though I think I will need more data under better darkness to bring them out. The Black Point may still be too low.

Boosted the saturation, but not quite as far, it didn't seem to need it.

Finally did another adaptive Subtract gradient removal before cropping for framing and to get rid of a few stacking artifacts around the edges.

Image is a 16 bit PNG, nearly 60 meg!

Edit: did a final WB to take out a slight red cast.

[AKB]

Well, call me picky, (and this IS far better than I have done with my own captures) and using knowledge I have gleaned from here on SGL, I see:

• some loss of blue? (might be my monitor)
• green still too high? (SCNR still does something)
• background fails the OLT (Olly Litmus Test)

Having said that, I like it!

[gnomus]

I think it is better, but I may be seeing some red now.  What does PS tellyou?

[DaveS]

I don't have PS, sorry. I have to do everything in AA.

Will have yet another look, but it may have to wait as I've some things needing to do (Lunch, then do a plum crumble for dinner)

 

Edit (For a second time) More important than either will be to get my monitor calibrated, time for a Colormunki or similar. It's a 4 year old Dell Ultrasharp, so probably going a bit off by now.

[gnomus]

1 minute ago, DaveS said:

I don't have PS, sorry. I have to do everything in AA.

Will have yet another look, but it may have to wait as I've some things needing to do (Lunch, then do a plum crumble for dinner)

Yikes.  I'd get PS before PI.  Others will disagree.

[DaveS]

I think I've taken this as far as I'm able to ATM. That's not saying it's perfect, far from it, but without a properly calibrated monitor I'm thrashing around in the dark to some extent.

So: Get some more data, you can never have too much . Looks like we may have a couple of clear nights coming up. But will they be dark enough?

Get my monitor calibrated. Been dithering long enough about this, time to actually do it.

Investigate PI with a view to purchasing a license.

Try to find an old, non-subscription version of PS.

Think that's enough for now .

[gnomus]

If you can't get an old version of PS then there is something called GiMP.  This may now be 16 bit - they have certainly been talking about it for long enough.  I saw some articles in AN regarding using GiMP.

I don't know about Photoshop Elements.  Perhaps someone else could chip in.

[DaveS]

Thanks, yes I'd just remembered GIMP. I hadn't bothered in the past because it was only 8 bit, but, like you, had heard of the upcoming 16 bit version. It had been upcoming for so long that I'd forgotten about it again .

Will give it a go.

[gnomus]

The joy of PS is that you can get a set of Actions for it called Noel's Actions which are really good.  I'm not sure if these work in Elements or in gimp.

[DaveS]

Well I checked out GIMP, and it's still only at 2.8.x, still 8 bit. Found 2.9 but it looks to be still under development and, I think, not available for Win.

 

Edit:

I've still been working on the data, trying to get rid of the green in the BG. Think I'm getting there but don't want to choke this thread up with yet more images until I've either got more data or given up.

Still need calibration though.

[SilverAstro]

1 hour ago, DaveS said:

Well I checked out GIMP, and it's still only at 2.8.x, still 8 bit. Found 2.9 but it looks to be still under development and, I think, not available for Win.

You are right it was a long time coming but it is now here !

and various builds of Gimp 2.9.x are available for Windows, the gimp downloads page ( https://www.gimp.org/downloads/ ) directs to ( http://nightly.darkrefraction.com/gimp/ ) for latest versions, both for Windows 32bit and Windows 64bit. I think they are installable versions. If you want a portable version to try out say on a usb drive (and simply delete from the usb folder if nolonger required ) then go to Paratha's Place (long well established and well regarded) at https://www.partha.com/ and on the right scroll way down there is a link to a Win64bit portable.

I am using a Win32bit portable on this laptop that I got from another forum/blog but I have mislaid the link at the mo., if you need Win32bit give me a shout and I'll dig a bit deeper

hth and have a happy playing