Fuzzy Select, Feathering, Hidden Areas Selecte

[peterpil19]

Hi,

I have been using GIMP for some time on my Macbook Pro. I use the fuzzy select tool to cut out the background of photos I take of coins so that I can show both sides of the coin in the one image with a white background.  I have an issue with using fuzzy select that would save me a huge amount of time, if I worked out how to use it better. Grateful for nay help.

I have 2 questions:

1.  When using the fuzzy select tool, why after feathering do selected areas outside the main selected area dissapear (screenshot 1) only to reappear when copying and pasting (screenshot 2 - circled). In other words, after feathering, it looks like i have gotten rid of the unwanted selected areas, only for them to reappear when I copy / cut from the selection (photo 2). If they were still selected, why aren't they showing as selected.

2. I struggle with silver coins as they are too reflective. Is there any way for the selection using the fuzzel tool to only include contiguous areas? Or is there a way to remove ALL selections outside the main selected area?  It would seem odd to me if there is no solution for this.  It is painstakingly slow to keep reducing the threshold and removing all unwanted selections. When I find myself doing this (usually with silever coins), I revert to the paths tool (also slow, but faster than using fuzzy tool in that situation).

Thanks, I hope to find out I've been using it wrong all this time and there is a better way to do it!

Peter P

[Blighty]

(05-12-2019, 02:44 AM)peterpil19 Wrote: When using the fuzzy select tool, why after feathering do selected areas outside the main selected area dissapear (screenshot 1) only to reappear when copying and pasting (screenshot 2 - circled).

A feathered selection means the selection is not binary. Pixels can be partially selected, ranging from 0% to 100% selected. The visible selection boundary (marching ants) indicates the 50% selected boundary. So you can have pixels that are 40% selected with no visible selection boundary. Don't use a feathered selection.

Quote:Or is there a way to remove ALL selections outside the main selected area?

You could try the selection tools with mode set to "Intersect with current selection". Make a rough selection and then select again with "Intersect with current selection" to refine the selection.

A grey coin on a grey background is never going to be plain sailing. Try photographing with a contrasting colour eg a green with no texture.

I am not sure if the jpg compression artifacts are in the original or just in the screenprint for the forum. These can also give problems.

The best way to remove a background is to
1) Make a selection and delete the background.
2) Grow the selection by 1 or 2 pixels
3) Use Colors > Color to Alpha to remove the background from the boundary between the coin and background. Change the default white to the background colour.

[Ofnuts]

1) because feathering creates pixels that are partially selected. The ants march on the 50% selection line, if you have an isolated area where the selection is below 50%, there won't be any ants to show it (but it can be visible with the "quickmask"). Feathering may not be the right technique to get rid of such areas.

2) The Fuzzy selector by design works on contiguous areas, so I don't really understand the question.

Something often overlooked is that the selection applies to all layers, so you can create a selection using one layer to cut another layer. In your case you could duplicate the layer, increase contrast on the copy to make the background almost completely white (as long as you don't create dents in the outline of the coins), make a selection from that, then hide the copy, activate the initial image and cut it with the selection.

But IMHO you would save a lot of time by taking the pictures on a contrasting background (red/green). Then you would be able to use color differences to select things.