GIMP cutting beyond selection

[JohnSmith]

I like to use the path tool to create a selection and then cut the selected area of the image. But for some reason lately, it's cutting sightly beyond my selection. This is only happening with the selections that are converted from a path and I can't figure out why.

[Blighty]

I can't repeat that. Perhaps it is the anti-aliasing pixels. Try Select > Sharpen and see if that helps.

[Ofnuts]

Can you make a small XCF with the Path and the generated selection, and attach it here?

[rich2005]

The selection from path takes the position of the path into consideration, some selected pixels on one side, some on the other.

   

Is that the problem?

[JohnSmith]

(05-09-2019, 06:34 AM)Blighty Wrote: I can't repeat that. Perhaps it is the anti-aliasing pixels. Try Select > Sharpen and see if that helps.

Yeah, I already did that. Sharpen does fix the problem, so it's not cutting outside the selection anymore, but the problem is when you sharpen the selection the selected area itself slightly changes, so it's still not cutting the exact pixels I want cut.

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(05-09-2019, 08:09 AM)rich2005 Wrote: The selection from path takes the position of the path into consideration, some selected pixels on one side, some on the other.



Is that the problem?

I don't think so? Once I do selection from path, the selection looks fine, exactly how I want it. But when I use cut, it cuts slightly outside the selection. This is also true if I use the paint tool for example. It will fill areas slightly outside the selection with the color.

[rich2005]

Then it is Ofnuts suggestion, post a small .xcf file with the path and active selection. Otherwise it becomes mainly guessing.

[Ofnuts]

(05-09-2019, 04:07 PM)JohnSmith Wrote:

(05-09-2019, 06:34 AM)Blighty Wrote: I can't repeat that. Perhaps it is the anti-aliasing pixels. Try Select > Sharpen and see if that helps.

Yeah, I already did that. Sharpen does fix the problem, so it's not cutting outside the selection anymore, but the problem is when you sharpen the selection the selected area itself slightly changes, so it's still not cutting the exact pixels I want cut.

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(05-09-2019, 08:09 AM)rich2005 Wrote: The selection from path takes the position of the path into consideration, some selected pixels on one side, some on the other.



Is that the problem?

I don't think so? Once I do selection from path, the selection looks fine, exactly how I want it. But when I use cut, it cuts slightly outside the selection. This is also true if I use the paint tool for example. It will fill areas slightly outside the selection with the color.

Without an image with path and ants together (see your question on GraphicDesign), hard to answer so making a guess:

* A path is infinitely thin, in other words pixels are much bigger than the path.
* When using the path for selection, pixels cannot be cut into smaller pieces. Instead, pixels that straddle the path are selected in proportion of their area which is inside the path. So most pixels that are on the path are partially selected.
* If you then cut the selection, the partially selected pixels are partially cut, the pixels in the clipboard are opaque in proportion to their selection value which is itself in proportion of their area in the path, and the pixels left in the layer are opaque in proportion of their non-selection which is itself their area not in the path.
* These partially transparent pixels of course have some area outside the path, but the result is visually smooth edges.
* Otherwise the only way to have exactly selected pixels with a path is to have path that exactly follows pixel boundaries.