[Techtalk] GIMP: Changing all set pixels to black

Miriam English mim at miriam-english.org
Tue Jan 19 04:46:32 UTC 2016

What are the odds? I just had exactly the same problem occur in a 
picture I was working on and I remembered that Akkana had answered your 
question much more accurately than I had, so I looked again at her 
answer and was going to attempt it to solve my problem when I stumbled 
upon an even better solution.

When going to Gimp's "Layer" menu and the "Transparency" submenu I was 
going to choose the "Remove Alpha Channel" item when I suddenly noticed 
the "Threshold Alpha..." item. Intrigued (I'd never used it before) I 
tried it and found it did exactly what I wanted and allowed me to tune 
exactly how much of the partly transparent black I wanted to make fully 
opaque black.

Thanks, David for the question and Akkana for your answer, without both 
I would likely never have found this neat function. It made my day. :)


	- Miriam

On 08/01/16 09:21, Akkana Peck wrote:
> David Sumbler writes:
>> so the pixels in the outline are not all black, but various
>> shades of grey.
>> I want the outline to be entirely black ...
>> If I use the colour picker on one of these grey pixels, it actually
>> produces black, so I think that they are not really grey at all, but
>> black with some degree of transparency.
>> The answer would seem to be to remove all transparency from the layer at
>> the outset.
> Remove Alpha Channel (in the right-click context menu for the layer
> in the Layers dialog) should remove any transparency from the layer.
> That will probably make the grey areas grey even if they were
> transparent black before. But at that point, you should be able to
> use Colors->Threshold and drag the slider all the way to the right
> to make them black again.
> At least I hope so. :-) If it doesn't work, post again (and it might
> help if you could upload the image, or at least the layer).
>          ...Akkana
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Website: http://miriam-english.org
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