Improved Aurora Borealis
I've added a basic local contrast stretching/tonemapping algorithm to the experimental regions of the GEGL codebase. I reused other ops for most of the functionality needed and coded it as a meta-op/macro op/graph op, with only a single specialized op to do the actual remapping. tried reusing as much code as possible. Since then I've been trying to make graphviz based visualization of GEGLs state (the nodes, graphs and properties). This allows to see how the tonemapper works, as well as closer inspection of the samples in GEGL gallery.
Putting together the pieces used to construct the contrast stretcher, would not be possible in a tree view such as the one used by the GEGL editor nor in OpenRaster using the hierarchical stacks, since it needs a node that has three inputs and one output to work properly. (Thus such macros/scripts should be DAGs like in the SVG Filter specification if OpenRaster is going to support this concept.
The tonemapper isn't good enough to properly with some of the OpenEXR test images (ugly sample). Even just adding a fader to allow controlling the amount will probably improve this situation slightly.
(Photograph of Aurora Borealis over Gjøvik by EJH)