Star Elimination

[tsaban]

Hi,

This is my first posting here.

After using PixInsight LE for some years I have converted to version 1.7 after the CEDIC 2011 conference. I am still learning how to use this great tool.

I wonder if there is a way to eliminate stars from an image?

I would appreciate any tips from you experienced guys.

Thanks
Tahir Saban

[Alejandro Tombolini]

Hi Tahir, welcome to the forum.

By eliminate stars, do you mean to separete them from the image to make some specific process?

Regards, Alejandro

[tsaban]

Yes. I know this can be done in Photoshop.

Tahir

[Alejandro Tombolini]

Hi Tahir,

It can be done easily using ATrousWaveletsTransform and PixelMath.

First duplicate your image and apply ATWT selection 7 ( or 8 ) layers and disabling "R" to the duplicate. This will generate only stars and some important nebulae structures

With PixelMath subtract "image duplicate" from "image" disabling Rescalate option.

Now you have "image" with the nebulae and "image duplicate" with stars and you can apply different process on them.

Finally with Pixel Math add "image duplicate" to "image" with Rescalete option enabled.

Regards,

Alejandro

[vicent_peris]

Hi Tahir,

I going to talk about this topic in the second article of my "Astrophotography with wavelets" series, in the upcoming PixInsight Magazine.


Best regards,
Vicent.

[tsaban]

Thank you Alejandro and Vincent. Looking forward to get the next issue of PixInsight magazine

Tahir

[troypiggo]

Excellent!  Been wondering this myself.  Looking forward to the magazine article.

I tried Alejandro's method above, but end up with lots of star halos and the nebulosity loses a lot of detail.  Do you recommend it be applied at the linear stage, or after histo stretch, or doesn't matter?  I need to play with the wavelet settings I think to see if it can be refined.

[wa4hnd]

Would this be similar to using the minimum filter in PS ?  I was going to post this question on the forum today till I saw this thread.   My question was

Is there something like a PS minimum filter in PixInsight or a process that would do the same thing?  That's about the only thing I use in PS anymore.  PixInsight is a great tool !

Al

[vicent_peris]

Would this be similar to using the minimum filter in PS ?  I was going to post this question on the forum today till I saw this thread.   My question was

Is there something like a PS minimum filter in PixInsight or a process that would do the same thing?  That's about the only thing I use in PS anymore.  PixInsight is a great tool !

Al

Hi Al,

In PixInsight you have the MorphologicalTransformation tool. It is under the Morphology section in the Process Explorer. There you have a lot more options than a minimum filter.


regards,
Vicent.

[wa4hnd]

Thanks Vicent,

I was sure PixInsight could do it, just didn't know where to look.  I just played some with it and yes it does what I was looking for... but with the lack of documentation it's going to take some practice to get the most out of it I fear...  Has anyone done any write ups on how best to use it?

One of you experts needs to write the do all end all book on PixInsight... I bet you'd sell a lot of copies ! <g>.

Thanks again,
   Al

[Nocturnal]

I think a search in the forum might give you some hints but in general this is how I use it (sometimes):

- create a star mask (a struggle in itself, sorry)
- apply the mask
- apply the erosion filter

I use small previews to narrow down on the right MT settings. Smaller and bigger structuring element and more and less amount. I think generally an amount of around 0.7 gives a desirable effect.

Not surprisingly Harry has a video on the topic. I haven't seen it but I'm sure it's excellent. A good idea to check there first. Perhaps even view all the videos if you're new to PI. It'll answer questions you didn't know yet you had.

http://www.harrysastroshed.com/pixinsighthomeinter.html

[RBA]

FWIW I wrote a tutorial on the subject, not to make the stars disappear but to reduce their visual impact.

Probably not nearly as fun as watching one of Harry's videos, but what the heck

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

Enjoy!

[jtheios]

This is fantastic, Rogelio. I knew the basics of MT, but learned some new tricks, especially 1) using HDR to tone down the galaxy before creating the star mask, 2) using the contours option to actually create the star ask, and 3) using ATW for sharpening the stars afterwards. Good stuff here.
Thanks, John

[sleshin]

Rogelio,

Great tutorial. Love it when you share your secrets. You are a gifted communicator.

Steve

[RBA]

Great tutorial. Love it when you share your secrets. You are a gifted communicator.

The HDRWT bit was actually a tip from some guy who goes under the name of Juan Conejero..., you may have heard about him
Before that, I sometimes would use curves, histogram, ATWT or other tools for a similar (or different) effect, but I have to admit the HDRWT works pretty well for that.