GIMP processed Andromeda

[steviemac500]

So this is the same shot from my earlier post. I had a go at processing through GIMP. I think its an improvement but I'd like other's opinions please?

Steve

[NGC 666]

It looks like you have a reasonable amount of data to play with, because the image is not that noisy - it has a good noise-to-signal ratio. However, your black point is set too harshly, meaning you're actually removing precious data! The black point is the darkest point of the image. The white balance is a bit off, too, but that's more to do with personal taste. I like it accurate to how the object looks to the eye (if you could see colour through a scope), but it doesn't have to be that way to be a pretty image. I have never personally used GIMP - instead, Photoshop. The stars are nice and circular and sharp, meaning your GoTo is doing it's job correctly (I assume you're using it to track?).

Just out of interest, what were your exposure times, number of frames and ISO?

If you want, you could send the raw stacked image (maybe a link) for others to have a go at editing. (I'm interested to try it)

[steviemac500]

Thanks, Id be interested to see what you could do with it, its hard when you don't know what your aiming for. How would I send the file, its 58 megs.

[cjdawson]

58Meg, sounds like a single frame?  If so, get out there and take a series of frames - more the merrier, then put the lens cap on and take another 20 frames.

That will give you a series of lights and darks.  You'll be amazed at that difference.

I'd also be interested in having a go a processing the image.   I'm also pretty much a begginner at that part, as I've been concentrating on the pre-processing side of things - just about getting there I think though.

[steviemac500]

HI, no it's 67 subs, only 24 darks as the remote gave up on me. The tif file is 58 Meg which is the one you would want to process? It's ISO is 800 at 70 secs each.

[steviemac500]

Here is a link. Hope it works.

http://astrob.in/209361/0/

[NGC 666]

Sorry, but I'm not sure how to download it. Google Drive or Dropbox or something?

[steviemac500]

If you click on the image you can copy it from there. It's now a png file as astrobin wouldn't accept tif.

[steviemac500]

Here's the link to the file on Dropbox.

https://www.dropbox.com/s/79r9fr03ft8iujf/Andromeda%20V1.TIF?dl=0&s=sl

[NGC 666]

I had two attempts, one in 16-bit, and one in 32-bit. The 16-bit happened to work better.

(In Photoshop:)

I used levels (black point/eyedropper) to get rid of light pollution, and the grey eyedropper in levels to change the colour. I also cheated a bit by darkening certain areas of gradient with the black eyedropper tool in levels, too. The Galaxy is a weird shape I think because it is difficult to separate the data with the gradients in the image. I also added the smart sharpen filter.

You didn't do too badly, considering this one is a VERY tricky photo to separate data from light pollution. More difficult than I thought. The only solution (unless filters) would be to get away from the lights, which I suffer from, too. What doesn't help is the fact that M31 is around the same colour as Light Pollution (or has relatively little colour anyway) - and is dim around the edges. So while it's not hard to photograph M31, it's hard to make a good photo of it - the spiral arms, ect...

Did you take flats and darks? How many subs did you take of what length?

Did you take photos in RAW format?

[NGC 666]

HI, no it's 67 subs, only 24 darks as the remote gave up on me. The tif file is 58 Meg which is the one you would want to process? It's ISO is 800 at 70 secs each.

Sorry, just read exposure specs. Flats would help remove the gradient - as I'm sure you've heard/read already, but especially so with an object like M31 which is largely affected by gradients because it is large and dim at the edges.

[laudropb]

Thanks for this very interesting post. I hope to start imaging soon and this is very useful

[NGC 666]

Also, bias frames will help remove those faint lines going across the image.

[steviemac500]

Thank you for doing this.

I'm glad I wasn't too far off but yours is definitely better to look at! I M31 is still a bit low in the sky in Cyprus which is where the pollution is coming from and I do think I over exposed too. I have managed to get hold of PS now so I'll be playing with that and I think I'll change target for a while to something higher in the sky.