Thanks guys.
Michael,
Very good question. I spent hours hand selecting reference points in IRIS to generate a polynomial background to be subtracted from each panel and I had to do two passes as well. Maybe there are easier ways with other software but I like the numerical approach and the total control that IRIS provides.
If you follow the links from this site,
https://arxiver.wordpress.com/2016/0...-periphery-ga/, you will be able to download a PDF paper, that I only found yesterday, with information on these faint structures.
Also Phil Hart showed me his unfinished version of the same field and his image shows exactly the same structures.