W.D.Clinger
Philosopher
That should terminate this entire contretemps.Here's the word straight from NASA. When they map the color values, the behavior of the pixels outside the limb is treated differently than the portion of the image over the disk. A gradient filter is applied to the image so the off-disk area will be enhanced to bring out details. That filter causes a discontinuity at the apparent limb because of a slight inequality of the radius of the filter and the solar image.
[qimg]http://img163.imageshack.us/img163/1843/sdoapodcolorcomp.jpg[/qimg]
The green line is there because of the processing. In this image, which I sent along with my communication in order to get a definitive reply, you see arrow "A" pointing to the edge of the filter applied in the image processing software. The arrow "B" is pointing to what amounts to the actual limb of the Sun. The apparent roughness of that "B" edge is due to the emissions picked up by the three filters used to make the composite, all of which are coming from above the photosphere.
Thanks, GeeMack.