NGC 253 LRGB

[rodmichael]

I imaged NGC 253 in LRGB over several nights in October. NGC 253 is currently very low on the Southern horizon in South Dakota, rising about 9:30PM and setting about 2:00AM (actually setting about 12:30AM for me due to an obstructing tree and a house). I was able to image about 2.5 hours each night.

Light pollution is substantial here (believe it or not) and my luminance sub-frames appeared unusable (despite use of an LP filter) so I extracted a synthetic luminance master from my combined RGB sub-frames. Total sub-frames obtained was 101, 5m each, unguided. Pre- and Post-processing was performed with PI 1.8.5.

I am very slowly learning to use PI (commensurate with my intellectual capacity), so I will be appreciative of any helpful criticism offered.

Full resolution image available here: http://www.astrobin.com/318315/?nc=user .

[rdryfoos]

Looks pretty good.  Seems a bit dark.  The RASA is a FAST scope, with big aperture, so signal should be very strong, especially with 8.4 hours of exposure time  maybe its the LP you mention?  That always plays havoc with me.  Did you use noise control in the galaxy?  It looks as though you did, and if so, I would say maybe a touch too much.  If not, then its something else.  Careful not to clip the low end (maybe why its a bit dark?) Space is not black.  If you make a star mask and expose only the stars you can bump up their saturation and get nicely colored stars.  I just realized that the focal length you using is small for the aperture, so the scale is not typical for galaxy hunting.  is this a crop?  That might explain things.

Great effort.  Keep at it. I find the smallest changes in the settings critical in Pixinsight.  An image can be transformed with the smallest setting manipulation. The devil is in the details as they say. 
Rodd

[rodmichael]

Thanks very much for your comments.

...Did you use noise control in the galaxy?  It looks as though you did, and if so, I would say maybe a touch too much.

When you say "noise control" do you mean noise reduction? If so, the answer is yes. I used MLT before HT and SCNR to remove green pixels after HT.

...I just realized that the focal length you're using is small for the aperture, so the scale is not typical for galaxy hunting.  is this a crop?

Yes, the image attached is a crop. However, I included a link to the full resolution image on Astrobin http://www.astrobin.com/318315/?nc=user.

I find the smallest changes in the settings critical in Pixinsight.  An image can be transformed with the smallest setting manipulation. The devil is in the details as they say.

I believe you. However, my numerous handicaps with PI include the "jargon" of post-processing which often leaves me completely unsure of what the different processes mean or do. So I am dependent to a very great extent upon trial and error to either learn what the jargon means or at least to learn what I don't like with different processes and settings.

[RickS]

Hi Rod,

That's not bad considering.  It's a much easier target for me down here in the Southern hemisphere 

I agree with Rodd.  Looks like you've gone a bit too heavy with noise reduction on the body of the galaxy and lost some detail.  It does look a little dark too.  You have black clipped the blue channel just slightly.

Cheers,
Rick.

[rodmichael]

Thanks, Rick. I'll see what I can do with the NR and the HT.

Clear skies.

[Geoff]

Nice pic Rod.  I would have stretched it a bit more.  However trying this I find that there is a distinct gradient if pushed to far--blue in the centre, brownish on the sides. 
Geoff 

[rodmichael]

I have revised the image a bit, including:
1. Redoing background modelization (ABE instead of DBE)
2. Re-did HT, less aggressive. Sky is less black (Is this what Warren Keller means by "stay gray?")
3. Changed TF parameters of LRGB combination (TF for Luminance = 0.30; TF for RGB = 0.20)

RESULT: Galactic Image is brighter; Center of galaxy has more color; galactic halo more prominent; Sky (as mentioned above) is less black; perhaps some detail lost with TGVDenoise.

Any Suggestions?

[RickS]

That's an improvement, Rod.  It still looks a bit soft.  Not sure if that's a result of processing or the quality of the original data.

Cheers,
Rick.

[rodmichael]

That's an improvement, Rod.  It still looks a bit soft.  Not sure if that's a result of processing or the quality of the original data.

Cheers,
Rick.

By "soft," I guess you mean the detail is not sharp, e.g., the dust clouds/lanes in the galactic structure or some overall fuzziness to the image.

Thanks.

[RickS]

By "soft," I guess you mean the detail is not sharp, e.g., the dust clouds/lanes in the galactic structure or some overall fuzziness to the image.

Yes, the fine detail is blurred.  Some of that is probably a result of shooting low in the sky.