A crack @ M31 processing (image not mine)

[dpastern]

Image data from:

http://www.mistisoftware.com/astronomy/index_fits.htm

In accordance with image usage rules:

Image Acquisition by Jim Misti and Steve Mazlin

I've done the processing using Photoshop CS2 and FITS Liberator, using the tutorials here (brilliant tutorials imho):

http://rdelsol.com/Presentations.html

In lieu of having clear skies to actually use my own scope/DSLR setup, I've taken to learning how to process astro images using other peoples. Since the owners of these data files are kind enough to 1) allow others to use, i.e. play around with them, and 2) post the resultant PP shots on websites etc, I'm hard @ work learning :-) This image has taken me a few hours of carefully following the tutorials etc. I've had a *lot* of fun doing this. I'm sure the image could be made better, this is really my first attempt!

Without further ado (large image download, may take some time to display):

http://www.macro-images.com/web/m31.jpg

I'd really like to thank both Jim Misti and Steve Mazlin for their kindness in offering these images to play with.

Cheers,

Dave

[chris.bailey]

I have played with the same data in the past and very good it is. Your process has blown out the core and clipped the black, the formeer being the major trick to imaging and processing M31.

[dpastern]

Yeah, I realised that I blew the core - hence the practicing :-)

Dave

[dpastern]

I'm not sure what you meant by clipping the black (or how you could tell so, unless you mean the histogram creeping up the black end?). Here's a 2nd attempt:

http://www.macro-images.com/web/m31core_final.jpg

Dave

[policy]

Wow! What a difference!

[chris.bailey]

Second is much much better and closer to what I got with the same data, core is still a little blown. Clipping the black is pretty obvious as empty space is not jet black. If you consider where that the in astrophotography all of the data is squeezed into a very narrow portion of the histogram, by clipping the backkground to black, you are loosing some of those photons you have worked so hard to get a hold of. If you avoid clipping the black with this data you will find that the faint outer reaches of M31 almost stretch from corner to corner.

[Nighthound]

You're making progress Dave and that's the goal. You did well.

To better demonstrate black point clipping I attached your image histogram and one from one of my attempts. I don't know how much total data was collected in your image so I realize I'm not comparing apples to apples in these two images but it does help demonstrate what "clipping" is and looks like.

As you can see all channels are pushed all the way left on your histogram graph. The red and blue channels being the most clipped. Try to aim for a histogram the peaks away from the left side as well as one that has all three channels peaking at the same area on the graph, this will insure better color balance. It's a good idea to keep the multi-channel histogram in view during the entire process to help keep an eye on color balance and clipping.

http://i3.photobucket.com/albums/y67/Nighthd/Astrophotography/test/tst2/clip.jpg

http://i3.photobucket.com/albums/y67/Nighthd/Astrophotography/test/tst2/noclipx.jpg

Hope this helps some.

[chris.bailey]

A quick play with that data gets. Core is still alittle hot (but then it is in the L channel of the data) and its a little green and has a bit of a gradient to it but you get the idea.

I have found the histogram in PS a bit insenstive for astro images and prefer the precision of PixInsight

[dpastern]

Ah good, the black clipping was what I thought you meant. I'll probably have another go at this during either this week, or probably the weekend where I have more time @ hand.

Chris - I did have the galaxy dust lanes that far extended at one stage during my processing, but added some contrast which ended up removing some of the dust on the outer edges.

Thanks Steve for the clipping visuals - excellent, I have some idea what I'm doing! And need to do.

A question - how did you both manage to present the core like that? It looks far nicer and more natural than my 2nd attempt, more gradual.

Thanks for the input, much appreciated.

Cheers,

Dave

[dpastern]

Oh, and Steve, that's the 2nd M31 shot I've seen with a lot of Blue nebulosity in it. I don't seem to be able to pull that out of the data, anything I'm missing?

Dave

[MidnightSun]

Nice progress and info. Processing is what I'm trying to get a handle on now. Just reading everything I can find and alot of practice......

[dpastern]

Nice progress and info. Processing is what I'm trying to get a handle on now. Just reading everything I can find and alot of practice......

That's what I'm doing Dave!

Dave