M31 in moonlight

[AndyBooth]

After a lapse of several months, finally got out Monday night for a rushed M31 with the moon
still near full, and a bit windy.
Startools did a great job of getting rid of gradients etc.

Comments very welcome.

Info page
http://www.astrobin.com/140001/

full pic
http://www.astrobin.com/full/140001/0/

regards,
Andy

[admin]

Look at those lovely dust lanes!
May I ask how you calibrated the colours? The stars and M31 could perhaps use a bit of (balanced) colour infusion - there are some interesting things going on in galaxies and their colours tell the story and history.

[AndyBooth]

Thanks Ivo.

"The stars and M31 could perhaps use a bit of (balanced) colour infusion "

If I knew what that meant I'd give it a go!

I just just clicked on a few stars in the colour module, and let it do its thing, tweaking a bit with the individual colour bias sliders.
I think i changed to 'artistic with detail' mode thingy.
oh, and Icapped green to brown.
I'm not very scientific when it comes to the processing, I make it look 'good' to me

Any instructions to try something different is very welcome!

regards,
Andy

[admin]

If I knew what that meant I'd give it a go!

Hehehe

Ok, right before you switch Tracking off, run the Color module.
Here you're looking for few things;

• A good even distribution of star temperatures, e.g. you should see just as many deep red, orange and white stars as blue stars in the foreground.
• For most galaxies, you'll be looking for a yellow core; older stars will be prevalent in the core as there is less star formation going on. This tends to shift the colour towards the red end of the spectrum as many of the bright blue stars will have burned through their fuel and will have died in this area. The outer rims, however, will typically see more star formation going on still, which is why the more luminous young blue stars will still be outshining the slow-burning redder and yellow stars. This is why these outer regions tend to the bluer part of the spectrum. In many galaxies you'll see purplish HII areas (this colour comes about due to the mixture of mostly dominant Ha and Hb emissions), much like our nebulae here in our milkyway.
• If applicable, dust tends to block out higher wavelengths more than lower ones, so any light that makes it through will tend to the redder end of the spectrum (ex. brown dust lanes, or the deep red light of an obscured star).
• It is rare to find an object that has dominant areas of green (OIII-dominant emssion excepted such as the Tarantula nebula or M42's core), so if the image has dominant green areas, reduce the Green Bias. You can use the MaxRGB viewing mode to see which channel is dominant - a very handy tool that even allows you to objectively colour balance an image on badly calibrated screens!

If you're imaging your color data with a light pollution filter in place, achieving a visually correct colour balance will be impossible, but you can still try to approximate one.
Do let me know if you have any trouble with this, or if you'd like me to have a go at your data.

[AndyBooth]

Thanks Ivo,
I'll give that a go.
And yes, I do use a light pollution filter, which does a great job, but does cause
havoc with the colour balance.


regards,
Andy

[AndyBooth]

OK Ivo,
I've had another go, processing to bring out more detail in the core and dust lanes, and
doing a lot more colour work.
What do you think, I like it a lot better than the first attempt which now looks bland to me.
ivo, any advice on howto get better stars? I.e. not such a marked core vs coloured rim transition?
Thanks for the input and help.

http://www.astrobin.com/141496/

regards,
Andy

m31fin.jpg (239.46 KiB) Viewed 10680 times

[admin]

OK Ivo,
I've had another go, processing to bring out more detail in the core and dust lanes, and
doing a lot more colour work.
What do you think, I like it a lot better than the first attempt which now looks bland to me.
ivo, any advice on howto get better stars? I.e. not such a marked core vs coloured rim transition?
Thanks for the input and help

You've certainly got the luminance/detail down pat! Great detail all round.
If I may nitpick, I'm still missing some colours, particularly in the blue spectrum. This could be due to the LP filter but most LP filter typically impact the yellow part of the spectrum, leaving blue and red relatively recoverable. Again, this may not be the case with this data. Though, if possible, I'd love to find out and see if I can give you any advice here for your particular setup. Any chance you could share the data with me to that end? (PM, e-mail, or in this thread)

The appearance of the stars don't strike me as problematic (colored halos like these are very informative from a scientific point of view when all star temperatures are represented), but if you don't this particular rendering of the colors you can reduce the 'Bright Saturation' parameter or switch the 'Style' to 'Artistic'.

[AndyBooth]

OK mate, will Dropbox a copy of the stacked only tiff tonight, no processing except flat, dark,and bias, and debayered.
All done in Nebulosity.

Thanks for the offer mate.


(Edit)
Here is the link:-
https://www.dropbox.com/s/9ljwn8u0sp4ai ... k.fit?dl=0

Regards,
Andy

[admin]

Thanks for taking the time to upload the data Andy - it's very useful!

Below is what I came up with, using fairly simple workflow - tweak to taste obviously.

m31stack.jpg (377.69 KiB) Viewed 10653 times

The good news is that I was able to recover mostly useful colouring - see workflow below.


--- Auto Develop
To see what we got. We can see a blue bias (typical). Oversampling (not unusual with DSLR data), some field flattening issues (elongation towards the corners). Stacking artifacts are also readily visible.
--- Bin
Firstly I bin to improve noise and make use of the oversampling.
Parameter [Scale] set to [(scale/noise reduction 50.00%)/(400.00%)/(+2.00 bits)]
--- Lens
In your case, the field isn't entirely flat. The Lens module can help in some instances and does a pretty decent job here too (one caveat being that diffraction spikes are no longer straight but slightly curvbed). A side effect of using the Lens module is that it (necessarily) cuts of some of the borders to make the data fill the whole image again ('Auto crop'). This has gotten rid of most of the stacking artifacts for us (bonus!), though a little bit remains.
Parameter [Center Y] set to [73 pixels]
Parameter [Curvature Linked] set to [125.42 %]
--- Crop
Getting of remaining artifacts and framing M31 to have its core in the center of the image.
Parameter [X1] set to [16 pixels]
Parameter [Y1] set to [9 pixels]
Parameter [X2] set to [1613 pixels (-50)]
Parameter [Y2] set to [1062 pixels (-52)]
--- Wipe
I roughly mask out M31, so that Wipe won't 'wipe' away any parts of M31. This is especially important at higher Aggressiveness settings.
A 'default' wipe yielded some issues in the corners. I don't know what the cause of this is - are your flats ok? That's why I used the Vignetting preset.
Parameter [Dark Anomaly Filter] set to [4 pixels]
Parameter [Corner Aggressiveness] set to [99 %]
Parameter [Aggressiveness] set to [75 %]
--- Auto Develop
For final stretch. I used an ROI over part of M31
Parameter [Ignore Fine Detail <] set to [2.4 pixels]
Parameter [Outside ROI Influence] set to [8 %]
--- Contrast
Default values, except Parameter [Dark Anomaly Filter] set to [3 pixels]
--- Deconvolution
Automatically generated mask.
Parameter [Radius] set to [1.8 pixels]
--- Wavelet Sharpen
Using same mask that Decon created.
Parameter [Amount] set to [242 %]
Parameter [Small Detail Bias] set to [93 %]
--- Color
Here's where it gets interesting...
I always apply the Color module towards the end (so it can recover the colour hue and saturation that was otherwise mangled by the luminance stretching).
As a matter of fact, it comes up with a pretty good color balance all by itself.

For M31, things to look out for are a yellowish core (present!), bluer outer rim (present!), some purple (or pinkish) HII areas dotted around the disk (also present!), and brown dust lanes (present!). This is not bad at all for LP filtered data. The only issue that betrays the LP filter is the star colors which are either blue or orange with few other temperatures in between. It's not a massive issue though. (as a side note, there are ways to get 'correct' colors and use an LP filter - do let me know if you're interested)

The only thing I had to really do is pull back on the green a little; looking at the image in the MaxRGB mode, we can see that the default values that ST came up with leave some areas that green-dominant. This is almost always a sign that the image is too green, as it is very rare to have such areas in outer space.

I setteled on Parameter [Green Bias Reduce] set to [1.49]

I upped the [Dark Saturation] parameter to about [6.80]; this introduces a bit more color saturation into the darker areas of the image.

Finally, I set Parameter [Cap Green] to [To Yellow], to remove any last bit of spurious green.

--- Wavelet De-Noise
To taste.

Again, this is a simple workflow and you should obviously tweak anything to taste. The big takeway is (hopefully) the usage of the Color module and what to look out for.

Hope this helps and happy holidays!

[AndyBooth]

Now Ivo, that is a great natural looking result!
Even got the Ha regions showing up -fantastic.
I've downloaded your routine and am going to try it tonight.
Smashing,
just the result I was looking for, thanks for taking the time to help.

And yes, please tell me how to mange colours when using LP filter, I have no choice but use it where I live!



best regards,
Andy