How can I stop GIMP's Fuzzy Select tool from over-selecting?

Question

I don't have a good way to explain this just using words, so here's a partial screenshot:

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Even when I set the threshold to 0, Fuzzy Select is grabbing a disproportionately large portion of an image. In the screenshot, I'm trying to only grab the darkest color. It's almost like there's an after-image stuck in the tool's settings. There's only one layer (with no layer mask) in the xcf, so it's not an issue of having the wrong layer selected.

Am I just flat-out doing something wrong? I tried messing with all of the other tool options, but haven't had luck.

Answer 1

Because it selects by color, and the difference between the black area and the near-black area is not color but opacity (you can use the Pointer dialog to check this). To achieve what you want:

• Layer>Transparency>Alpha to selection to generate a selection based on transparency
• Select>Selection editor to open the selection editor. You will get a "negative" of your image (white is what is fully selected, and the "Alpha to selection" selects pixels according to their opacity).
• Click on the white part (this acts as a "Select by color" on the selection values) and this should restrict your selection to the fully opaque bits.

Alternative method:

• Layer>Transparency>Alpha to selection to generate a selection base don transparency
• Select>Save to channel to save the selection. At that point the saved channel is the "active drawable" and so the Paint tools will act on it.
• Use the Threshold tool to remove the gray band.
• In the Channels list, right click and Channel to selection to make a selection from the result.

Answer 2

I think the problem is because you have different areas of transparency - but the Fuzzy select tool works by comparing differences in colour.

Here's a workaround that might solve it for you.

1. Create a white background layer below the image layer/s, and enable its visibility.
2. Set the fuzzy select tool options to Select by: Composite and Sample Merged
3. Try to make your selection again.
4. When you have finished, you can hide the background layer visibility, or just delete it.