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My friend is able to take long exposure photos of stars, but these photos need to be combined into 1 photo to create an image of star trails.

What software can do this?

She does not have Photoshop, so recommendations that also work without Photoshop would be appreciated.

OS: Windows. Price: Willing to pay up to $US10 for the software.

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    I assume that software should work on Windows? Any price/license concerns (must it be free, or how much would the friend be willing to pay, must the license permit for commercial use)?
    – Izzy
    May 2, 2016 at 5:14
  • Would panorama software work? For example Hugin. I assume the photos are all from the same point and at the same angle, so the software would be stacking the images. I believe Hugin does that. hugin.sourceforge.net and hugin.sourceforge.net/docs/manual/Align_a_stack_of_photos.html Preventing the black sky in one image from obscuring the trails in another might be a problem.
    – JKEngineer
    May 5, 2016 at 21:24

1 Answer 1

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Lots of tutorials on the net for how to make star trails using gimp which is a free, open source, cross platform and very powerful photo editing tool.

One that I found that was nice and concise was this and the processing steps were:

  • Open up GIMP.
  • Add all the images into layers. There is no specific order required.
  • Change the blending mode of all the layers to Lighten. In GIMP select each layer and change the blending mode in the layers dock (top right). You should now have a star trail.

If your camera needed some processing time between each photo, resulting in something resembling LEDs: continue with:

  • Flatten your image (Image>Flatten)
  • Select a group of star trails that have roughly the same angle (pointing in the same direction). Go to Filters>Blur>Motion Blur… adjust the angle by dragging the angle slider and keep an eye on the effect in the preview window.
  • Repeat the above step for all angles of star trails.

enter image description here

There are even some gimp plugins to automate the process for the user, such as GIMP Star Trails Compositor or StarTrails for videos.

enter image description here

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  • How many photos would this work for? If you tried to load thousands of layers, I suspect GIMP would run out of memory or crash.
    – vclaw
    May 2, 2016 at 17:52
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    @vclaw - I think that if you tried it in any way but incrementally for 1000s of high definition photos anything but a super computer would crash. Just take the first 30 combine to one, add 30 & combine etc. May 2, 2016 at 17:56

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