Alternate Technique For Removing Stars (Update)

[STEVE333]

This updated technique is performed using PixInsight. PixInsight includes the Starnet process to remove stars and it is oftentimes all that is needed. However, sometimes Starnet leaves artifacts, and, this technique usually provides a "cleaner" final starless version.

This technique first removes most of the stars and then goes back and removes the remaining faint stars. The result is a virtually starless image with no discernable artifacts. The first part of the technique was created by Jeremy Scheary (hope I spelled it correctly). It was presented in a recent tutorial on IP4AP (a source of short and concise online PixInsight tutorials) who kindly allowed me to share this with forum members. The second part of the technique was created by Jim Thommes. I added a little bit in the middle .

This image of the Elephant's Trunk Nebula will be converted to a starless image.

I have created a set of Process Icons to carry out the creation of the starless image. They can be downloaded from the DropBox link below.

https://www.dropbox.com/s/ssrqtqbfkeehf ... .xpsm?dl=0

Here is what you will download.

Starless Icons.JPG (19.64 KiB) Viewed 1642 times

With the Process Icons it only takes about 5-10 minutes to create a starless image on my machine (a bit longer for images heavily populated with stars). Here is how to do it:

1) Open the StarMask process (1st icon) and it will look like what is shown below.

Apply this process to the original image. Adjust the Noise threshold if necessary.

2) Drag the Binarize (second icon) apply triangle onto the star-mask image to binarize the the stars.

3) Invert (3rd icon) the star_mask image. DON'T FORGET THIS STEP!!

4) Open the DefectMap process (4th icon) and make sure the name in the "Defect map" box matches the name of your just created star_mask. Adjust any other settings to agree with those in the picture below. Make sure Square is selected for the Structure setting.

Apply the process to the original (not the star_mask) image. This will remove the majority of the stars from the image.

5) Very large stars will not be removed by the above processes. They can either be left as is, or, I prefer to use CloneStamp to remove them as shown in the side-by-side pictures below. Your choice.

6) The final task is to remove the remaining dim stars. Open StarMask (5th icon) and change the Working mode to Structure Detection. Change the rest of the settings to match the image below. Noise threshold can be adjusted if necessary.

Apply this process to the "starless" image. This will create a structure_map of the remaining faint stars. The detected stars will appear very dim in the structure_map, but, don't worry.

7) Blur the structure_map with the Convolution process (6th icon) with settings as shown below. The structure_map may appear "empty" but don't worry, the information is there.

8) Stretch the blurred structure_map using HistogramTransformation (7th icon) until the stars show approximately as shown in the picture below.

9) Apply the structure_map as a mask to the "starless" image. Open MorphologicalTransformation (8th icon) and adjust the settings to match those shown below.

Apply MorphologicalTransformation to the "starless" image to remove the remaining dim stars. The side-by-side images below compare a closeup view before the dim stars are removed and after the dim stars are removed.

DONE!!

You now have a starless image.

Below is the final starless version.

Hope you find this helpful. Thanks to those who made this possible.

Steve

[XCalRocketMan]

I need to try this out. I have a few images that Starnet produces those ugly black and white artifacts. And thanks for including the Process Icons!

[STEVE333]

I need to try this out. I have a few images that Starnet produces those ugly black and white artifacts. And thanks for including the Process Icons!

You're welcome. Hope it works as well for you as it has for me. If you don't mine, would you let me know how it works for you?

Cheers,

Steve

[XCalRocketMan]

I need to try this out. I have a few images that Starnet produces those ugly black and white artifacts. And thanks for including the Process Icons!

You're welcome. Hope it works as well for you as it has for me. If you don't mine, would you let me know how it works for you?

Cheers,

Steve

Tried it last evening on my Rosette in SHO. Here is the result. This is only a single test but this process is thus far a welcome addition to my post-processing toolset!

[STEVE333]

Looks like it did a good job! Well done.

Thanks for the feedback.

Steve