Star reduction in super widefield images

[petercoxphoto]

Hi folks -
I'm very much a newbie with PI and have hit my head against a bit of a brick wall. I've included a recent very widefield image of Orion extending up into Perseus. This was made with a 24mm lens on a Canon 5D Mk II. It consists of 25 x 10 minute lights made at f/5.6, about 40 dark frames and 20 each of bias and flats. The image has been run through DBE (twice!) to get rid of gradients in the lower portion of the image - mainly due to high haze and minor light pollution from a nearby village. It's also had ColourCalibration run on it.



I'm having two problems with it. First, in order for the brighter stars in the constellations and the faint nebulosity to stand out more, I want to reduce the influence of the smaller stars in the rest of the frame. I've tried doing this with varying options using a star mask and MT, but I can't get something that looks natural when seen close-up. The sheer number of tiny stars makes it very difficult.

Does anyone have advice on how best to do this on an image like this?

Secondly, as I said above, I ran the image through DBE twice to remove the gradient. However, I can't seem to get rid of the remaining gradient in the lower left using this tool. It's not a massive problem as I can just selectively desaturate that area in Photoshop, but I'd prefer not to have to. Any insight here?

Thanks for your help!

Cheers,
Peter

[oldwexi]

Hi Peter!
No need at all to use P.....! PI has more for astrophotography as the Painting Software will ever have.
Simple DBE removes your lower left gradient.
Find the link for my screenshot where i use DBE and the parameter which i used in my try.
http://www.werbeagentur.org/oldwexi/fotos/orion_widefield_prep.jpg
Left the final result, right the list of all processes i used and their parameter...
Aloha
Gerald

[petercoxphoto]

Hi Gerald -
Thanks for your help, it's much appreciated. Your screenshot is very helpful, thanks. Can you please explain what you did in the two pixelmath instances? You created a clone of the image and made a change to it, applying that to the original in some way?

Cheers,
Peter

[pfile]

it's pretty hard to get all those small stars with a 'traditional' starmask.

RBA has some tutorials on his website. the crux of it is that you use the atrous wavelets tool to extract only the smallest scales of your image, and use that as the starmask for MT. although i don't see him discussing it, you can use the MT tool to "open up" the star mask a little bit using the Dilation or Opening modes of MT.

at step 4 of this tutorial he discusses it:

http://blog.deepskycolors.com/archivo/2010/05/01/luminance-Processing--Making-the-Ifn-p.html

he also has a full tutorial about MT and star reduction, but this one happens to use the starmask tool to create the mask.

http://blog.deepskycolors.com/archive/2011/09/08/star-size-reduction-via-Morphological-.html

rob

[petercoxphoto]

Hi Rob -
Thanks for those links - that was very helpful. Much more natural-looking star reduction than what I was doing before.

Cheers,
Peter