A common technique in astronomical photography is to combine a number of images, taken around the same time, which results in a target image with added clarity. This is called stacking and there exists specialised software to do this.

Does Gimp have the functionality required to do this? Is anyone using Gimp for this purpose? If so can you please outline the steps taken?

David

Maybe in the layers dialogue change each layer mode from 'normal' to 'screen'.

Check out this page for a set of astronomy tools for gimp. Never used them, but I recalled seeing them

http://hennigbuam.de/georg/gimp.html

-Rob A>

No! There are some plugins that attempt to align images for HDR purposes, but I have not found anything adequate to the job of focus stacking.

I use this technique a great deal in producing photographs of insects to illustrate keys.

If you want open source, try Hugin. You can use align_image_stack.exe to do the necessary image alignment and adjust magnification (but maybe that is not necessary for Astronomy) and then enfuse.exe to do the actual image merging.

Helicon Focus is probably the leading commercial package. The results from Hugin and Helicon are indistiguishable in my tests, but Helicon has a nice user interface and is much faster because it makes better use of multiple CPUs (align_image_stack is single threaded, enfuse has a limited multi-threaded version). There is a free 30-day trial version of Helicon and the licence is not expensive.

I use GIMP to do the post-processing once I have a completed stack. Often needs all the usual exposure adjustments, rotation, etc. - and removal of specimen pins.

Stuart writes:

No! There are some plugins that attempt to align images for HDR purposes, but I have not found anything adequate to the job of focus stacking.

I use this technique a great deal in producing photographs of insects to illustrate keys.

If you want open source, try Hugin. You can use align_image_stack.exe to do the necessary image alignment and adjust magnification (but maybe that is not necessary for Astronomy) and then enfuse.exe to do the actual image merging.

Helicon Focus is probably the leading commercial package. The results from Hugin and Helicon are indistiguishable in my tests, but Helicon has a nice user interface and is much faster because it makes better use of multiple CPUs (align_image_stack is single threaded, enfuse has a limited multi-threaded version). There is a free 30-day trial version of Helicon and the licence is not expensive.

I use GIMP to do the post-processing once I have a completed stack. Often needs all the usual exposure adjustments, rotation, etc. - and removal of specimen pins.

Darktable also does HDR as of version 0.8 :) See http://darktable.sourceforge.net/ I haven't tried it yet.

See also http://garmahis.com/tutorials/hdr-tutorial-free-software/ and http://qtpfsgui.sourceforge.net/