Removing stars from an image using StarNet++

Using the free StarNet++ software, you can remove stars from an image, leaving only the background (nebula or galaxy). This makes it possible to save the stars separately in a graphic editor (for example, Adobe Photoshop), which ultimately allows you to process the stars separately, the background separately, using different parameters for noise reduction, saturation, etc. In addition, a picture without stars can be quite self-sufficient due to a more interesting display of the nebula.
You can download StarNet++ from the link. The program is free, does not require installation – just unpack the archive, open the folder and run the starnetGUI.exe file. If an error occurs during startup (missing DLL VCRUNTIME140_1.dll), try downloading and installing Microsoft Visual Studio, and then rerun starnetGUI.exe.

The training image file can be downloaded from this link. This is a fragment of an image of the IC 2118 “Witch’s Head” nebula in the constellation Eridanus, which I photographed on November 11, 2023 using a fast Samyang 135mm f/2 ED UMC Canon EF lens, a Canon 550Da DSLR and a Sky-Watcher AZ-GTi mount in equatorial mode . The total signal accumulation was 58 minutes.

The method for removing stars is very simple.
1. The source file must be in TIFF 16 bit format. I usually remove stars after stacking the frames and converting the histogram (for example, in GraXpert).
2. Launch StarNet++, press the BROWSE button, specify the path to the image with stars and open it.


3. In the second line, you need to add a number or word at the end of the file (for example, 2 or starless).


4. Press the RUN button, a black window with percentages appears. We wait. The processing time depends on the file resolution and the computer processor.

5. After the processing process is completed, another one will appear next to the original file (with the previously specified word – for example, starless). Total – two images, one with stars and nebula, the other – only with nebula.

To select ONLY the stars into a separate image, you will need a graphic editor (for example, Adobe Photoshop).
6. Open both files (original and without stars) in Photoshop.
7. Select and copy one of the images (key combinations CTRL + A, CTRL + C), then select another image and overlay the copied image on top of it (CTRL + V).

8. In the layer blending mode settings, select DIFFERENCE


9. We flatten the layers by right-clicking on one of the layers and selecting the appropriate item from the context menu.


10. “Save the file as” under a different name (for example, stars only).

Done, now there are three files – the original (stars + nebula), only the nebula and only the stars. You can work with these files individually (background alignment, noise reduction, levels, curves, saturation, etc.)

To combine the nebula image and the star image, you need to open the already processed images in Photoshop. For training, you can simply try to collect files without additional processing.
11. Select and copy one of the images (key combinations CTRL + A, CTRL + C), then select another image and overlay the copied image on top of it (CTRL + V).
12. In the layer blending mode settings, select LINEAR DODGE (ADD). At this stage, you can separately rotate the levels and curves for each layer separately (for example, slightly dim the stars).


13. We flatten the layers.

14. “Save the file as” under a different name (for example, final). Ready!

This whole process is on video (without sound):

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