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I'm sure this is easy; I just don't know the words to find it on the google.

I have an image. I want to create a new image of the same size. Some of the new image will be white. Some will be black. No other colours. I want to use the polygon selection tool on the original image to mark out the area that should be white. Everything outside that region should be black.

I can get as far as marking out the polygon with the selection tool. Then, I thrash around with tools and search engines, trying to find a way to do what I want.

Can someone put me out of my misery?

Edit: By request, a sample of the final output. There used to be a whole lot of other things here. I drew a polygon over a bit of it, filled the polygon in with one colour (black), and filled in the rest with a different colour (white). An example of the final image

Solid colour. Inside the polygon one colour. Outside the polygon a different colour. I create the polygon by drawing it onto an existing image; the existing image dictates the shape of the polygon, and also dictates the size of the new image (i.e. exactly the same). Not greyscale. Inside the polygon one colour. Outside the polygon a different colour. Every pixel in the image will be one of only two colours.

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    Could you post an image with an example of what you are trying to do? When you say "2 tone" do you mean that the image will actually be 2 colors (only 100% black or white pixels) or that it will be gray scale? It sounds like you're just trying to fill a selection with a solid color. – Scribblemacher Sep 21 '15 at 16:16
  • I have edited the question. Is "fill a selection with a solid colour" what I should be googling for? I was trying "mask" and "layer" :( – Moschops Sep 21 '15 at 19:19
  • Scribblemacher, "fill a selection" was the magic search phrase. If you write that in an answer rather than a comment I'll upvote it and mark it as the answer :) – Moschops Sep 22 '15 at 9:40
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What you want to do is fill the selection. You can do this using the Edit > Fill with FG Color Ctrl+, or by using the Bucket Tool.

If using the Bucket Tool, select the Bucket Tool Shift+B, and then Shift+click inside the selection. This will fill the selection with the current foreground color.

As MichaelSchumacher mentions in the comments, using the Bucket tool like this can cause some feathering around the edge of the selection.

  • This can result in more than two colors (or at least, different levels of saturation of the fill color). Selections, especially if their edges aren't aligned to the x and y axis, can be partial, a pixel can e.g. be selected by only 50%, and will then be filled by 50% gray* when filling the selection with with black. (* or something close to that). – Michael Schumacher Sep 22 '15 at 20:16
  • I actually ended up doing it using "Edit->Fill With Foreground Colour", and then inverted the selection and repeated, but you told me the magic search words "fill selection", so you get the points :) – Moschops Sep 23 '15 at 14:38
  • @MichaelSchumacher Hmm, that's actually never happened to me, but I'll edit my answer accordingly. – Scribblemacher Sep 23 '15 at 15:16
  • Create a triangular selection and fill it. Then zoom in to its edges. In general, what I did describe will happen. – Michael Schumacher Sep 23 '15 at 15:23

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