stacking star trails on a mac

<p>Hi all,<br>

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.<br>

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.<br>

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.</p>

<p>Thanks for the help!</p>

<p>The most simple thing you can do is with ImageMagick:<br>

<br /> convert image1 image2 -compose lighten -composite result<br>

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.</p>

<p>I haven't done any stacking myself but I did some research on this a while back for a client. <br /><br /> Mac Singularity is a site for astronomers and astrophysicists using Mac OS X systems: <br /> <a href="http://macsingularity.org/" target="new1">macsingularity.org</a> <br /><br /> And they have a good Wiki page too: <br /> <a href="http://macsingularity.org/astrowiki/tiki-index.php?page=Mac+Astronomers+Wiki" target="ne2"> macsingularity.org/astrowiki/...</a> <br /><br /> I'm sure there are links to image stacking/coalescing software available there somewhere. ;-)</p>

<p>There's also IRAF from NOAO:<br>

http://iraf.noao.edu/</p>

<p>Adam,</p>

<p>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!</p>