Circle specific color for highlighting objects in maps

[mrplow]

I have some rather large maps which have some fine details which are difficult to locate while looking at the entire map. What I would do in gimp is to select by color, expand selection by 1000px, feather, fill, shrink by 200px, feather, delete.
I have, however, over 80 maps and due to their large size they're real memory hogs.
Any help would be appreciated.

[snibgo]

You could turn all other colours black and turn the required colour white (possibly with fuzz).

Then dilate and erode with morphology.

Feather with blur.

I don't understand your other operations, but they are probably easy in IM. From the greyscale version I outline above, you could highlight the map, like using a highlighter pen. Or do something else.

Gimp is 8-bit. IM is usually 16-bit, so uses twice as much memory. You could use Q8 IM.