Quote:
Originally Posted by jase
Impressive narrowband work for the DSLR, Mariusz.
Forget the minimum filter. If you do decide to use it, make sure you upsize your image first. minimum filter will just reduce star sizes, it will not get rid of the purple halos. There is a quick and dirty by using the PS selection tool on highlights. This will get most of the bright stars. Or a more comprehensive method by creating a specific star mask of which I've noted below. both the quick and dirty and more comprehensive end in the same way i.e. the use of the saturation tool to drop the purple tone. You can get fancy and use the selective colour tool too. You'll find the comprehensive method by Russ is far superior. I use it regularly. You may need to increase the high pass radius depending on the data set.
Star Selection (from Russ Croman):
- Make a grayscale copy of the image. I'll call this image #2.
- High-pass filter image #2 with a radius of one pixel.
- Apply a Gaussian blur to image #2 with a radius of one pixel.
- Invoke Image->Adjust->Threshold.
- Adjust the Threshold Level one click at a time until just the stars are white and everything else is black.
- In the original image, in the Channels Palette, create a new channel. Name it "Stars." Choose "color indicates masked areas."
- Paste image #2 into this channel.
- Make just the RGB channels visible (i.e. make the Stars channel invisible).
- Discard image #2.
- In the original image, invoke Select->Load Selection. Choose the Stars channel you just created.
- Invoke Select->Expand and expand the selection by a few pixels (e.g., three).
- Voila!
|
Thank you for the tip... I'll give your procedure a go and post the result.
Quote:
Originally Posted by strongmanmike
Hard work at F10 but a good result there Mariusz 
A good tip from Jase too
Mike |
I don't think its that hard to autoguided track at that focal length with my CGEM. Once I PA it seems to be accurate enough to give me round stars in up to 45 minutes subs (longest I tried so far). I only lost a couple of subs in the last few months and all were due to clouds moving over the object/guide star
, and once due to forgetting to plug in the autoguide cable...
and so accumulated periodic error did what periodic error does.
Now I'm going to try to get the bounce about the zero line in the PHD graph to be lower since I seem to be getting quite rhythmical spikes above and below it. Hopefully smoothing out the guide corrections will tighten the stars and overall image details will be sharper.
Mariusz
