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To remove shadows and grain from the background we can chose a threshold for values of transparency and of opacity when using the "Color to Alpha" tool in Gimp 2.10: Simply drag the sliders until you are happy with the result. On a white background your image will then look like this: Alternatively you can make a colour selection with the select by colour ...


9

You can clean the picture first, for instance using Levels: the big peak on the right is the original background. This shows that the background is not pure white. If you use C2A without preprocessing, you have to aim for this color. The white handle is dragged to the left (left edge of the background peak), so that most of the background becomes pure white....


2

Ok. I figured it out. I just removed the opacity for both layers, merged them, and put back the opacity. It's just one shade of gray now!


1

(Didn't watch the video) For Opacity Masks (which is what you've described) to mask everything entirely you need to ensure the black you are using is 100C/100M/100Y/100K or 0R/0G/0B -- all channels need to be solid on the mask. Basically, use the "Registration" swatch. If you simply use 100% K in areas on the mask, they will be a dark grey and not fully ...


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