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Fuzzy selecting makes part of picture more transparent..
#1
I want to get rid of the liquid from the mug so I fuzzy selected with a threshold 90 the coffee part, but when I clear it the pink part directly above it becomes more transparent. Why does it do this?? I'll probably just make a path instead but just wondering...


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#2
How do you clear? Edit>Clear? I don't see anything pink above the coffee...  IMHO a threshold of 90 is way too much for this. And check in the tool options that "Feather edges" is not selected.

Btw, as said earlier, the right technique to remove the coffee is

* Fuzzy select
* Select>Grow by 1px
* Color>Color to alpha

This ensures nice and clean edges... Here, have a nice cuppa:

   
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#3
Yes, some of the coffee color is in that brown area and a fuzzy select with a threshold of 90 selects it. Not called fuzzy for nothing Wink

A Gimp 2.10 tip see: https://i.imgur.com/qKurxgZ.jpg

1. Bottom of the fuzzy select is a tick box labeled 'Draw Mask' That overlays the selection with a magenta mask, you see that the brown area is also affected.

2. Still in the fuzzy select tool, you can click and drag to adjust the threshold and the change is shown in the mask. You actually need a threshold round the 50 mark.

3. Let go the mouse, the adjusted selection remains and cuts as shown.
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#4
The marching ants you see are just a close approximation to what you are selecting. If the colors are close enough, it might select some of that color too, but not enough to make the marching ants go around that part.

Try using a lower threshold if this happens, or of course use the path tool. If it is a simple shape, the path tool is almost always the best option.
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#5
(12-08-2019, 08:41 PM)Ofnuts Wrote: How do you clear? Edit>Clear? I don't see anything pink above the coffee...  IMHO a threshold of 90 is way too much for this. And check in the tool options that "Feather edges" is not selected.

Btw, as said earlier, the right technique to remove the coffee is

* Fuzzy select
* Select>Grow by 1px
* Color>Color to alpha

This ensures nice and clean edges... Here, have a nice cuppa:
I just press delete on the keyboard, does the same thing. Here is a picture of what happened when I did it
And yes feather edges is off
https://imgur.com/a/YnR45rI
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#6
Yes, got it... Un-check the "anti-aliasing" in the options... or use a more reasonable threshold.
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#7
(12-08-2019, 08:43 PM)rich2005 Wrote: Yes, some of the coffee color is in that brown area and a fuzzy select with a threshold of 90 selects it. Not called fuzzy for nothing Wink

A Gimp 2.10 tip  see:  https://i.imgur.com/qKurxgZ.jpg

1. Bottom of the fuzzy select is a tick box labeled 'Draw Mask' That overlays the selection with a magenta mask, you see that the brown area is also affected.

2. Still in the fuzzy select tool, you can click and drag to adjust the threshold and the change is shown in the mask.  You actually need a threshold round the 50 mark.

3. Let go the mouse, the adjusted selection remains and cuts as shown.

When I put on draw mask and click, the magenta color just seems to highlight the same area as the dotted line selection does. Not sure what difference the mask makes?

(12-08-2019, 09:42 PM)Ofnuts Wrote: Yes, got it... Un-check the "anti-aliasing" in the options... or use a more reasonable threshold.

yes you're right it was the high threshold that was doing it, turning the anti-aliasing off didn't prevent it at 90. It's just weird because the lines doesn't show it going outside the coffee area..seems odd it would do that unpredictably?
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#8
(12-08-2019, 10:26 PM)marigolden Wrote: It's just weird because the lines doesn't show it going outside the coffee area..seems odd it would do that unpredictably?

I mentioned this in my post above:

"The marching ants you see are just a close approximation to what you are selecting. If the colors are close enough, it might select some of that color too, but not enough to make the marching ants go around that part."


Also as Rich mentioned:
"Not called fuzzy for nothing [Image: wink.png]"

There are ways to wrangle these selection tools to bend them to your will, but they are not exact which is why you have controls for threshold, feathering, anti-aliasing, etc.. The best way to see what you are actually selecting is to tick the option 'Draw Mask' as Rich suggested. Then you can drag your mouse to adjust your threshold and see how it is affecting the surrounding areas.

Keep at it and you'll get there.
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#9
The "marching ants" follow a line where pixels are more than half selected on one side, and less that half selected on the other.They mark the true edge of the selection only for "sharp" selections, where everything is fully selected or not selected at all but with 'Anti-aliasing' you implicitly accepted some partial selection to happen. Then, when you delete, these partially selected pixels are partially deleted, and so become partially transparent.
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