[ptx] gimp/krita help in removing artifacts

[Michael Galloway]

this is a bit off topic perhaps, but i could use a bit of help with gimp/krita in managing
layer masks to mask out stitching inconsistancies. i was working thru this tutorial:

http://homepage.ntlworld.com/j.houghton/pttute.htm

but not being a graphics oriented person i just don't know how to do this with gimp/krita. 
if someone knows of a good example on how to do this i would really appreciate a link. 

also, i don't really know what output to use from hugin to use to fix these kinds of errors.
is it best to use a multi layer tiff or multiple tiffs?

thanks!

-- michael