StarXterminator process [Deep Sky] Processing techniques · Patrick Graham · 1/26/2023 · 10 · 739 · 0

Does anyone have any guidance on how to recombine an image after using the StarXterminator process.  I successfully created a starts image only and was able to reduce the number of stars without creating artifacts.  How to reintegrate the "reduced star" image  back into to the subject image is  not known to me.  I think it might be with Pixel Math but I'm not experienced enough yet to know how to use it.


Also,  any tips on where to insert this into the processing flow.  After integration:  DBE, NoiseXterminator, BlurXterminator, GHS stretch, Curve Transformation (saturation and color enhancement).

Thanks in advance

CS 
Patrick

Hey Patrick,

I found this little formula some time ago and use it to either remove stars using the pre- and post- StarXT images. I have found it works really well.

So process with Star XT to generate the Starless image, this gives PostStarXT. Then plug the Pre- and Post- images into the Pixelmath formula as follwos:

For generating 'star mask' with PixelMaths:
~((~Pre-StarXT)/(~PostStarXT)) - this gives the 'Star Mask'

The play around with the 'Star Mask" to get colour and stretching right.

The recombine the 'Star Mask' back with the Starless image again using the following PixelMaths formula:

For combining stars back with PixelMaths:
~((~PostStarXT)*(~Star Mask)) with Create New Image

Re where to insert it, I usually do it just prior to stretching.

Give it a go.

Cheers

Paul

I use the Blend script using the Screen method to blend a starless image with the stars image.  BlurXTerminator is pretty good at reducing star sizes without separating out the stars.

Jeff

I use this method in Pixelmath and it works very well, which is in fact, the screen blend process in Pixelmath form:  

combine(ImageX,ImageY,op_screen())

I cut and paste that formula into the Expression Editor, then find the two images I am trying to combine from the picklist on the right.  Simply replace ImageX with of your images, and ImageY with the other.   I then go back out of expression editor, and select New Image as the destination; drag the triangle to either image and you'll have your combined image!  By creating a new image, you can go back and tweak your original images and just keep recreating new versions. 

As far as when, I like to separate in the linear state (though have experimented with both), that way I can clear up some of the noise before stretching; as a Canon DSLR user, I also use the Canon Banding Artifact script on the starless image far more effectively than the combined image. This also allows me to stretch stars and starless fields separately and I can pay much better attention to star color/saturation/cores.  I find I have to use HSV Repair far less often when I stretch the stars separate from the non-stellar images.  I don't recombine until both are processed in the non-linear state towards the end. Usually the only thing I will do after combining is tinker with star reduction using Bill Blanshan's formulas.   

Clear Skies!

Rob

Glad to help! The thing with that script is always check the box to Protect Highlights and to orient the bands horizontally for the script to work; sometimes images need to be rotated for the script to work, then I rotate back. With an image with bands but a full starfield, you will get some artifacts in line with bright stars/objects, so the I have found the script is way more useful on the starless images with far fewer artifacts. I'll sometimes run it once or twice.  Good luck!

Patrick,

this very topic is outlined in great detail by Russell Croman, himself, here:

https://pixinsight.com/forum/index.php?threads/unscreening-and-re-screening-recombining-stars-with-starless-images.18602/

CS
Chris

PS: I do the non-linear processing in Photoshop - there you just set the star layer to blending mode "screen" - that's it.