Trying out a corona image processing technique given by Fred Espenak (and my own tweaks on it for use in GIMP)
1) Crop your base image to a square, centered on the center of the Sun.
2) Make a duplicate of this layer and rotate it about 5 degrees clockwise. Set the opacity to 33%. Make another duplicate of the layer and rotate it counterclockwise. Again set to 33% opacity.
3) Merge these two rotated layers with a copy of your base layer. The effect of this is to blur the original image through that angle, yielding something like this:
4) Now set this new, radially blurred layer above a copy of your base layer, and set the mode to Grain Extract.
Merging them will produce a new layer which contains details of the corona, without the brightness information:
5) Set the mode of this "detail layer" to Hard Light
. Merging with a copy of the base layer will now emphasize those corona details:
This is just a quick and dirty proof of concept, but it seems to work pretty well and really brings out the finer details, especially in the radial spokes emanating from the poles of the Sun. I'm sure with some of the better photos that Harbinger and others took it may yield some very stunning results.