PixInsight Forum (historical)

PixInsight => General => Off-topic => Topic started by: Ken Pendlebury on 2010 September 06 18:32:25

Title: So many stars...
Post by: Ken Pendlebury on 2010 September 06 18:32:25: Hoping somebody can help here...

Below you can see my first attempt at the crescent nebula. I am concerned because there are SO MANY stars that they actually drown out the DSO. Is there a way to tame these stars without affecting the nebula (too much)? Thanks for any tips.

Ken

(http://www.crossfitgeorgetown.com/ken/CN/LRGB_CN.jpg)
Title: Re: So many stars...
Post by: Nocturnal on 2010 September 06 19:58:25: You could try creating a star mask and then applying a morphological transformation with an erosion filter. Search the forum for some of those terms for more information.
Title: Re: So many stars...
Post by: Ken Pendlebury on 2010 September 07 09:36:25: Thanks Sander. I was at a loss for what search terms to use. Using your suggestions, I was able to dig up some information. I will give it a go and report back.

Thanks again,
Ken
Title: Re: So many stars...
Post by: Nocturnal on 2010 September 07 09:47:19: Hi Ken,

that's a common problem and not just here on this forum. How do you search for something when you don't know how -others- describe it?
Title: Re: So many stars...
Post by: Carlos Milovic on 2010 September 07 10:52:33: Hi Ken

I played a bit with your image. Another alternative to build the mask is to use the gradient (see the GradientMapper process I uploaded). You may modify it a bit with curves or HT to fine tune it, but it basically will target the outer regions of the stars, leaving low contrast features and the star cores untouched.
See the attached images. The second one has curves on it, to increase contrast and saturation.
Title: Re: So many stars...
Post by: Carlos Milovic on 2010 September 07 10:53:09: and the modified version...
Title: Re: So many stars...
Post by: Ken Pendlebury on 2010 September 07 11:34:00: Wow! Thanks Carlos!

Did you ever build GradientMapper for the Mac?
Title: Re: So many stars...
Post by: Harry page on 2010 September 07 11:51:06: Hi

Of course there is a video on how to do it http://www.harrysastroshed.com/mask.html (http://www.harrysastroshed.com/mask.html) :P

Harry
Title: Re: So many stars...
Post by: Carlos Milovic on 2010 September 07 13:37:00: No, sorry :( But Juan wrote a few days ago a simple script that performs the same task. See his latest posts in the development subforums.
Title: Re: So many stars...
Post by: Ken Pendlebury on 2010 September 07 14:14:00: Thanks Harry. I will check out your video and try it out...

Carlos, Sorry to be a pain, but I can't locate any scripts by Juan that might match your description (in the lat 30 days).

Regards,
Ken
Title: Re: So many stars...
Post by: Carlos Milovic on 2010 September 07 14:36:36: http://pixinsight.com/forum/index.php?topic=2228.msg14630;topicseen#msg14630

;)
Title: Re: So many stars...
Post by: Ken Pendlebury on 2010 September 07 21:03:41: Thanks to all who helped me out here. I ended up going with the script that Juan wrote in order to generate the star mask and then used Harry's excellent tutorial in order to get a handle on erosion (MT).

After this, I used some admittedly heavy ACDNR because the minimized stars now appeared as noise (to me). Inspecting the image at full scale clearly shows artifacts indicative of ACDNR abuse ;). I will say that I prefer this artifacting over the noisier "minimized" version...

Here is the wide field page with all sizes:
http://www.flickr.com/photos/kenastro/4970111770/sizes/l/in/photostream/

Here is the crop page with al sizes:
http://www.flickr.com/photos/kenastro/4970100530/sizes/l/in/photostream/

Thanks again,
Ken
Title: Re: So many stars...
Post by: Nocturnal on 2010 September 08 06:30:07: Hi Ken,

I think you did great work reducing star sizes but now stars that are close together seem to have blended into one, giving the impression of many small lines or dots with 'commas' instead of dots. This looks a little odd.
Title: Re: So many stars...
Post by: Ken Pendlebury on 2010 September 08 07:16:39: Ok... maybe I'm off base about the "pre-ACDNR" noise level... I will post this one up a bit later.

Thanks for the feedback.
Title: Re: So many stars...
Post by: Harry page on 2010 September 08 12:26:34: Hi

Like most tool you have to be how much you use them >:D

With the morph tool try using a smaller amount try 0.1 and more iterations ( i have used up to 10 ) , this can give better results ;)

Also when using the star mask , I almost ignore the small stars so they do not get mushed ;D

Just a thought

Harry
Title: Re: So many stars...
Post by: Ken Pendlebury on 2010 September 08 20:17:25: Thanks for all the help... I am really struggling with this one.

No ACDNR after MT leaves a significant amount of star noise over the DSO, ACDNR and too much MT leaves odd looking star lines. I have tried many variation of MT from 10 iterations of 0.1 to 1 iteration of 1.0. Each of these ends up with images that are indistinguishable from one another. The mask I have created is from the gradient script that Juan wrote. Taking Harry's advice, I tweaked the histogram on this to darken areas around very small stars. Using this for the mask did not seem to give any significant advantage as the end product seems to look the same.

Here is the latest I have come up with that only has "minimal" joining of very close stars:
(http://www.crossfitgeorgetown.com/ken/CN/cresc_no_acdnr.jpg)

Here is the one I posted yesterday:
(http://www.crossfitgeorgetown.com/ken/CN/cresc_acdnr.jpg)

Am I just going about this the wrong way? Maybe I am being oversensitive to noise? Any thoughts are appreciated. I am here to learn.

Regards,
Ken
Title: Re: So many stars...
Post by: Carlos Milovic on 2010 September 08 22:36:40: I think you are going in the right path. The minimalist version looks way better than the other, in this monitor :)