a new stairtrail python plugin , the author would be glad to have some feedback l
for the the code and more info
http://code.google.com/p/gimp-startrail-compositor/

I don't know what to use as frames. I made two, one for the light folder and one for the dark folder using a gradient. The images are the same. I got a black image.

Hi the plug-ins goal is to auto stack star trail images so you get a nice streak across the sky. The Light frames are added using lighten and dark frames using difference. The light frames are the shots of the sky with long exposure times of around 30s. Over this amount of time you can start to see the rotation of the earth, so the stars appears as short lines. Dark frames are taken with the same settings and in the same ambient conditions as the light but with the lens cap on so as to create an image of the sensor noise. By stacking 139 of them all you get something like:



The plugin first creates a black image so when you layer over the light frames with lighten you are starting from nothing as it where. The dark frames are then differenced to help reduce the noise and any hot pixels from the image.

If no images are found to layer you just get the black starter image. One of my todos is to count layers as they are added and then warn if none are found. What image extensions did you use as there's a white list of image types so I don't try open a non image file and crash out. The list is currently jpg, jpeg, tiff, tif, bmp and png.

Very cool - thanks for sharing the script with us.
Welcome to Gimp Chat by the way.

Thanks, while the actual code is fairly simple and didn't take long it took me hours to get it working at all as the main python documentation register command simply didn't work. It was only once I found the templates I got it working then added in all my code. Seems the documentation is due an update.

Now i just have to get off my lazy hind end and take some night images.

After spending my lunch reading up I have realised I am dealing with the dark frames completely wrong

Made a start on updating the code to do it properly and also had a go at removing the need to specify width and height.

Question: how do I average a set of frames? Do I just add each new layer at half the opacity of the last? So 1st 100% 2nd 50% 3rd 25 etc. Ideally I'd use median to bin outliers but that's more complex than I fancy working out!

All done, 1.2 release now on google code

not sure but if to add white frames lighten only works well, it was no possible do the opposite for the darkframes using darken only ?

I hope is not a too dumb question i found hard read the code (not your in particular , just in general ) where maybe is evident why is needed another solution

I'll say! I had to search the information around the web from different sources... The official gimp python documentation is quite lacking. I had to patch together stuff from the script-fu specs, procedure database, other scripts, etc. before I got a good understanding of gimp-python...

Have you looked at this: http://hennigbuam.de/georg/gimp.html

Anyway, to stack all at equal resultant opacity is 1/L for each susequent layer:

1/n.
.
1/5 (20%)
1/4 (25%)
1/3 (33.333%)
1/2 (50%)
1/1 (100%)

-Rob A>