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here's a map of a country with a red border: https://upload.wikimedia.org/wikipedia/commons/1/13/Congo_Kinshasa_Topography.png

i've imported the .png and now want to clip it to just show what's inside the red border.

tracing results in a huge complicated mess of paths and nodes that basically cause inkscape to hang when i try to intersect/difference them with pencil-drawn paths to try to isolate the border.

i feel like i must not be approaching this correctly, what's the right way to do it?

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Hi there and welcome to GDSE.

As you might know the image you have is a raster image which consists of pixels.

Inkscape is a vector drawing application. You can place/import raster images, but you can't directly manipulate the pixels.

As you have experienced your image is way to complicated to do an automated trace.

I recommend you to do one of the following:

  1. Open the image in a raster image application (Photoshop, GIMP etc.) and erase/mask the unwanted area manually (there are many different ways to do this).

  2. Use Inkscape to manually trace the contour using pen tool and then use this shape as a clipping mask for the image.

  3. Find another similar image in svg format (which is a vector based format). Open it in Inkscape and delete the unwanted paths.

  • the image isn't too complicated for a trace, see my answer. i just had to experiment with the trace options a bit. – user1441998 Oct 10 '18 at 0:21
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The red border is part of the PNG. It's not a vector, so you can't use it as a clipping mask. It's not possible. Inkscape is a vector image editor.

However it is possible to add a vector clipping mask to a raster image in Inkscape. But the process is manual, and involves drawing the clipping mask manually.

  • Create a closed path with the Bézier tool, around the area you wish to clip.
  • Select both the path and raster image
  • Click Object > Clip > Set

Here's a quick example. I have drawn a closed shape filled with semi-transparent orange so you can see it. I select both the raster and the path, then clip it.

enter image description here

  • i want an exact clip, as automated as possible. see my answer, it is possible, i just had to understand trace options a little better. – user1441998 Oct 10 '18 at 0:22
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a color multi scan trace isolates the red (i used 24 colors but i think you could use less). i found the red one, moved it to another layer, and deleted the rest. then i broke it apart, found the resulting path for the contiguous border, moved it to another layer, and deleted the rest. since the border isn't a closed path (there's a little opening at the coastline), i then had to use the pencil tool, path intersection/difference operations, and another break apart, etc, to get rid of extraneous nodes. then a linked offset, edited its radius to -0.5 in xml editor, and i had a perfect clip.

  • this stack exchange requires me to wait to accept this answer, but as far as i know this is the most exact and automated method. – user1441998 Oct 10 '18 at 0:23
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On the page, where your PNG can be found, there is a SVG file too, two pictures above.

I would download this one, and see, whether the details are fine enough for my needs.

  • Thanks, but I'm interested in keeping the topography information in the png – user1441998 Oct 24 '18 at 22:27

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