Invert selection feature doesn't apply to the crop tool.

Inverting crop selection would be useful in removing black bars from letterboxed images, for instance:

letterboxed image

  • (autocrop and zealous crop don't entirely remove unwanted area from this image) – user598527 Jul 20 '17 at 20:23
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    Because they remove uniform colors and the black margins are far from uniform. Start Windows>Dockable dialogs>Histogram and make a selection on the full width of a margin, you will see a rather wide range of black values. – xenoid Jul 20 '17 at 21:34
  • @xenoid: Yes, I noticed that when zooming in. Perhaps YouTube's compression (image source) causes this. – user598527 Jul 20 '17 at 22:09
  • I've now removed the demonstration image as I feel that it doesn't in any way improve the question. – user598527 Jul 20 '17 at 22:11
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    But the question without image is useless... Anyway if what you want to do is keep the image at the center, then you select it wit the crop tool and don't need to invert the selection. You can also use a rectangle select and Image>Crop to selection (again, no need to invert anything). In both cases, the crop keeps the selection and sheds what wasn't selected. – xenoid Jul 21 '17 at 0:20

It would be easier to just use the Rectangle Select Tool...

  • Click-drag around what you want to keep

  • Go to Image > Crop to Selection

Gimp Menu

And done. Save it out...

enter image description here

  • Your answer applies to this specific image, but doesn't answer the question. I've only used the image as an example, "How to invert crop selection?" is the question. Perhaps I shouldn't have added the image in the first place. – user598527 Jul 20 '17 at 22:08
  • I've now removed the image. – user598527 Jul 20 '17 at 22:11
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    No I'm pretty sure my answer applies to any image at all. Make a selection and crop. That's it. – BANG Jul 21 '17 at 0:29

You are mistaking the Crop tool for a selection tool. It isn't. There is a Rectangle selection tool for this, and the selection it creates can be inverted.

Now, on your image:

  • If you want to restrict the image to its center and remove the dark margins, then you use the Crop tool, and there is no need to invert the selection.
  • If you want to delete the dark margins without changing the size of the layer image, then you use a Rectangle selection on the part you want to keep, then Select>Invert and Edit>Clear.
  • If you want to keep the dark margins, then you use a Rectangle selection on the part you want to delete, then Edit>Clear.

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