Re: [Gimp-user] Gimp newbie trying to get a job done.

Hi Brent,

I expect that you want more than just the green selection - you want what the green selection would be if there were no roads/other data overlaid, right?

The best way I can do this in a reasonably automated fashion is:

1) Extract the roads as a selection
1-a) Colors->Components->Decompose, RGB, delete all but Green channel
1-b) Levels, adjust so that only roads are black and everything else is white (be fairly generous with what you call a road - a little slop is better than too little road)
1-c) Copy (control-C)
2) Back in original image, Create a new layer, transparent, select it as active layer.
3) Quick Mask
4) Paste (Control-V), Anchor (Control-H)
5) Quick Mask off
6) Select->Invert
6) Select->Grow (2)
7) Fill with white (drag from toolbox)
8) Select->None

At this point you should have 2 layers; the top has all the roads covered by white, and the bottom your original map image

9) Run the G'MIC plug-in (probably a separate download, google for it), select Region Inpainting, OK with defaults
Wait a few seconds, and you now have a map that has just green and grey regions with no red or hints of roads.
10) Delete the top layer that's no longer useful.

At this point the problem of extracting what you really want (an in-filled green image) can begin.  Its a bit messy with your image due to compression artifacts, but you can get decent results doing a Select by Color with threshold=28, then Select->Shrink(1) followed by Select->Grow(1) to get rid of the smallest objects, but there's still some garbage in the final results.  Color-To-Alpha with white and then black can also produce a semi-transparent image, but its got a lot of noise (other colors existed in the image that are now really noticeable).  Experimenting with Posterize or other color reduction/smoothing may be beneficial too, just to remove compression artifacts.

This isn't suitable for anything scientific - the infill process is certainly making guesses based on surrounding data which just doesn't exist in the image - but hopefully it'll get you at least part of the way to where you want to be.  You could script most of this once you find values that work for you (though figuring out the G'MIC plug-in may be tough as it just takes a string input in non-interactive mode).

Happy GIMPing,

Seth Burgess

On Wed, Jan 25, 2012 at 7:56 AM, Brent Shifley <Brent Shifley arkansas gov> wrote:



                I have been using your app extensively since November.  I have come up with a real need to perform in Gimp, but I do not know if Gimp can do it.


                What I am trying to do is import a PDF that contains a graphic of radiation patterns from RF towers, along with all roads and other geographical data.  Once imported, I want to remove all of the roads and unwanted data and keep the radiation pattern.  The radiation pattern is in 1 color that dominates the image, and “covers” most of the other unwanted info, almost as a 50% transparency.  I then want to export the radiation pattern, and use it in Google Earth.  Additionally, where the radiation pattern is not, have it become completely transparent


                Can you tell me how to perform this feat using Gimp?


Brent Shifley

AWIN Support


Arkansas Wireless Information Network (AWIN)


AWIN Operations arkansas gov


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