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Tutorial:
Gimp for astrophotography


Content:

Note:
I take no responsibility or liability for what are written here, you use the information at your own risk!


Separation of stars and DSO, part 1.3:

Invert:

Separation of stars and Deep Sky Objects, Gimp

Invert the selected area. The stars will be selected instead of the background. The white preview window change to black. It's now the srats that are selected.


Expand the selected area:

Separation of stars and Deep Sky Objects, Gimp

With the Tool 'Grow' we can expand the selected area.


Setup Grow:

Separation of stars and Deep Sky Objects, Gimp

Select how much the selected are shall expand. Something around 3 pixels.


New selected area:

Separation of stars and Deep Sky Objects, Gimp

The border of the selected area is now outside the stars.


Feather:

Separation of stars and Deep Sky Objects, Gimp

We don't want to have the mask to be just on or off, with the Feather tool we can make a soft transit. Set it something like 2 to 4 pixels, you will not see any difference in this image.


Copy to new layers:

Separation of stars and Deep Sky Objects, Gimp

Make a new group of layer, name it 'DSO mask'. Move the 'Stars + DSO copy' and 'Stars 1' layers into it. Make a new copy of the group. Rename it to 'Star mask'. The layer 'Star 1' and 'Star 2' are identical, but can't have the same name.


Add a Layer Mask:

Separation of stars and Deep Sky Objects, Gimp

Right click on the 'DSO mask', add a layer mask to it.


Selection:

Separation of stars and Deep Sky Objects, Gimp

Choose the 'Selection' and click add.

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Next: Separation of stars and DSO, part 1.4

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