star masking revisited

[dhalliday]

OK
You all seem so helpful here...I am naturally going to see if I can test your patience...
I wrote a while ago about star masks...
Mostly I was told how tricky they are 

I am currently working on an image;
http://www.flickr.com/photos/daveh56/3933874999/sizes/l/

Here obviously my stars are all blown to he

Here I have started to try harder to mask them,which I now realize I must do fairly early in the histo routine...(duh !!)
My result (early) is;
http://www.flickr.com/photos/daveh56/3934155907/sizes/l/


So now my stars have these bad "halos" around them...(which I see in many astrophoto's...)
They look more twinkly,and starlike though...so I am moving (maybe) in the right direction.
Now here comes the patience test..
Is this halo correctable by making bigger/smaller  or maybe darker/lighter stars in the mask?

The settings in star mask do not exactly come with a "detailed" explanation !!

Is there a tutorial on these settings..??
Can you say  a few words on it?
Also,can I make a small "preview mask of an area?
Is this a faster way to play around with the parameters...it does not seem correspondingly faster...
Could you post a picture,perhaps,of what a good star mask would look like for my image,if I just show you a JPEG version of it.
I know uploading tif files is tedious,and I am bad at it...and I for sure don't really want to go that route...
Maybe better you could just show a (very small,but magnified) veiw of what some fairly unprocessed stars (any stars !),and the corresponding good mask.

Not a week goes by that I do not find a trick in Pix to improve my results!!
Thank you

Dave

[Simon Hicks]

Hi Dave,

Regarding making a small preview area to fiddle (optimise) with the star mask parameters. Unfortunately StarMask applied to a Preview actually analyses the whole image. That's why it takes just as long. There are reasons for this that Juan has can explain.....something to do with looking at all of the wavelet scales in the image.

However, there is a great little 'cheat' that will get you 99% of the way there. Create a small Preview that grabs a range of star sizes of interest. Then just grab the image name tab at the side of the image and drag it onto another area....this creates a parent image from the Preview. Now create a Preview of that parent image that is roughly the full size of that parent. Now when you apply StarMask to that preview, it will give you a StarMask really quickly.....because the parent image is actually really small as well.......so you can play with the parameters.

Once you are happy then just apply the StarMask to the original image.

Cheers
         Simon

[Niall Saunders]

Once you are happy then just apply the StarMask to the original image.

But, be prepared to have to possibly make slight adjustments once you are dealing with the 'full' image. At the very least, make sure that your 'final' star mask seems acceptable.

Cheers,

[dhalliday]

Hmmmm
I think maybe I will just create a "super cropped" image and play with it.
But that advice you gave is going to save me time...
One last stab at "free/easy" advise on this topic though;
Is it best to do a sort of "halfway" histo stretch on an image,and THEN generate the star mask?

Take M45,for example...(which I have not "GOT" well yet...) .......
Those stars turn into monsters..! but many images I see have a sort of a "halo" around the star...presumably from suboptimal masking...
But then the CLEANEST mask (I guess) would be from a fairly "un stretched" star.....
Someone...save me a few hours and comment on this!
I feel a lot more like I am back in grade 7 violin class,at this point...but I am aspiring to be a "rock star",on stage...
Help me become/generate a "perfect" star !!

Dave

[Simon Hicks]

Hi Dave,

Others will have different advice....but here's my two pennies worth. Unfortunately star masks need different characteristics for different usages. Sometimes they need to be very large and soft, sometimes small and tight depending on what you are try to achieve. But on the whole, larger softer masks are better....most of the time.

Star masks are hard!  And they come back to bite you in the bum after another 10 stages of processing.

Cheers
         Simon

[David Serrano]

Create a small Preview that grabs a range of star sizes of interest. Then just grab the image name tab at the side of the image and drag it onto another area....this creates a parent image from the Preview. Now create a Preview of that parent image that is roughly the full size of that parent.

You can create a preview that is exactly the same size of the parent by dragging the image tab to an empty space in the tab selector (ie dragging downwards).