- brushes...  suck.  If you need a different size brush:
    - File > Dialogs > Brushes
    - New brush
    - pick one with the desired size, name it the same as the others with the right (s) size
    - Save


- to remove vignette, when there's a white background:
    - duplicate
    - select all the bits where there isn't white
    - invert
    - run the plugin "Resynthesis" on it
    - change the layer to "divide"
        ....  this fixes the white levels....  but what about the black?


- to fix black levels for lines:
    - run DifferenceOfGuasian
    - multiply that against the image
    - merge down
        (we now have enhanced lines at least, but not the rest of the image)
    - diff that against the original image

    - pull up the channels dialog, and copy one of the channels to the selection
    - invert selection
    - run "Resynthesis"
    
    alternatively:
    - take the diff, and desaturate it
    - dump it out as a .rgb raw file
    - write a custom program that finds the local maximum for every point...   eg. at every point,
      search the neighborhood a bit...   if there's a brighter pixel nearby, then change this pixel
      to be that bright