M31 processing issues; ?HDR

[jambouk]

Is there a plug in, or a simple way to reduce the brightness of the core of M31 whilst bringing up the brightness of the spiral arms, using GIMP?

Thanks for any replies.

James

[ollypenrice]

You don't need a plug-in. EIther the data is in your capture or it isn't and you can, reasonably easily, find out. When you look at the linear image, what does the core look like? How big is the bright blob in the middle? It isn't going to get any smaller whatever you do. (So far as I know.) But, as you stretch, how much bigger is it going to get? The answer you want, I presume, is 'as little as possible.' But you do want to stretch the faint stuff.

I find that the easiest way is to do different stretches, hard for the faint stuff and delicate for the core, and blend them in layers. I don't know if GIMP supports this routine. Learning to shape the curve during the stretch is the key thing. Experimenting is the way to learn and we are all still learning.

Olly

[lensman57]

Is there a plug in, or a simple way to reduce the brightness of the core of M31 whilst bringing up the brightness of the spiral arms, using GIMP?

Thanks for any replies.

James

Hi James,

M31 needs a short set of exposures for the core and a much  longer one for the other bits. The usual way of dealing with this is to blend the two sets in PS in layers and allow the core to show through. In the old times Gimp wouldn't allow 16 bit ops in layers   perhaps they have improved the software. If you have a dedicated AP software such as StarTools or PI you could try to recover detail using HDR wavelets but be warned Olly is not too fond of HDR treatment and TBH unless it is done very delicately I tend to agree with him as the image could look like it has black tape worms.

A.G

[jambouk]

It's not my data, i'masking for a friend. But i will pass the info on; thanks for the comments

[jambouk]

[ollypenrice]

In the image above there is a very hard cutoff between the bright core and the area around it. Careful management in curves could avoid this, I reckon.

Olly

[IanL]

I'd be very surprised if you needed to go down the HDR route with M31 with multiple exposure lengths - M42 needs it, but I can't think of much else that does.  The example below is 6 x 30 minute exposures at F6.3 with an unmodded DSLR.  I supposed if you went for long exposures on a really fast scope then you might be able to blow out the core, but looking at the over-stretched version above there isn't enough in the outer arms to suggest that is the problem here.

As Olly said, I think you just need to work on the initial stretch - don't blow out the core by trying to get all the details in the arms in one operation.  Do enough of a stretch so you can see what you've got without blowing the core and then tweak the fainter stuff in to visibility using multiple iterations of curves.

[Andy Milner]

Hi all, i imaged m31 fir the first time last night. I'm a beginner and I understand all that's been said above. But if anyone coul bullet point a list of techniques or types of workflow I should consider I would appreciate it. I will then look up tutorials on this. I've looked in the past and all I find is various tutorials on how to do a layer mask, etc, but no real idea if which technique to do first and in what order. Apologies for novice question. Cheers! Andy.

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[Andy Milner]

Hi all managed to answer this myself..I've found this tutorial. And it's really good. I've learned slot from this.. www.myastronomyjournal.com/DSLR-AIP/C002-M31-Walkthrough/

It should help anyone else with processing M31

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