How to competently turn a monotonous background into transparency? (p-shop, gimp)?

Question

GIMP

It is necessary to obtain images from icons with blurry edges that look normal on different substrates. If the background transparency is made a selection, background impurities remain on the blurry boundaries of objects: if the background was white, then white, if gray, then gray. How to get rid of the background color impurity altogether, turning it into opacity? Are there semi-automated techniques whose operations are built into the editor? Not necessarily the easy way, because it is clear that there is no general way to separate the background.

Answer 1

This is done through alpha channels.

Answer 2

Selection - Feather Edges?

Answer 3

Select the area with the required transparent color, then "Color"->"Color to Alpha Channel".
If the blurred edges are uniform, then you can achieve the correct selection of the removed color using feathering.
If the drawing has a complex structure, then we use the "Quick Mask" and manual processing.

Answer 4

In PS, you need to manually or with the help of plugins make a mask.
In GIMP, as far as I know, there is a function you need - to make a given color transparent, taking into account impurities.

Answer 5

I usually use the top sliders ( the top ones for the current layer ) Blend if in the Blending Options… of the layer, or if something more complex, then draw a mask with handles or select the Magic Wand Tool, which is sometimes quite simple. If you create a mask, you can first create it in a separate channel, mixing the original channels in different combinations through Apply Image ... in it in different combinations and applying curves to them, but this is a completely perverse way worthy of Margulis. If there is a chroma key in the background, then you can simply extract it in the Lab space using the same Blend if. There are a lot of ways in PS.