stacking star trails on a mac

Discussion in 'Digital Darkroom' started by xpiotiavos, Jul 20, 2009.

  1. Hi all,
    I'm starting to dabble in star trail photography, and read about the technique of taking a series of consecutive shorter exposures and stacking them together, rather than taking a single long exposure.
    So I decided to try it out, and now have 186 30" exposures that need stacking. The question now is: how in the world do I stack that many images? I use GIMP and am familiar with stacking images using the opaqueness sliders, but I don't want to even think about how long it would take me to stack 186 files using that technique.
    Is there a software program available for the mac that will stack the images for me? I can't seem to find anything using google, etc.
    Thanks for the help!
  2. The most simple thing you can do is with ImageMagick:

    convert image1 image2 -compose lighten -composite result
    This requires input images to be perfectly aligned on pixel scale. It also does not mask out any cosmics/bad pixels. In gimp, the overlay mode "lighten only" in the layers window does the same.
  3. I haven't done any stacking myself but I did some research on this a while back for a client.

    Mac Singularity is a site for astronomers and astrophysicists using Mac OS X systems:

    And they have a good Wiki page too:

    I'm sure there are links to image stacking/coalescing software available there somewhere. ;-)
    There's also IRAF from NOAO:
  4. Adam,
    Two programs I've used for blending multiple exposures that may work for you are ImageFuser and XFuse. Both are Mac programs and both are donationware. I don't know if either will work with as many images as you have; let us know!

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