How do I change white background in Paint.NET to transparent when the edges are blurry

Question

If you take an existing image that has a shape on a white background and you want to make the background transparent it's relatively simple to use the magic wand tool to select the background, delete it and then save the image as .gif or .png.

But that only works if the edges are solid and there's no zone where white is mixed with the color of the shape.

However, if you have an image like this: https://i.stack.imgur.com/evuFa.jpg where the color changes gradually from solid color of the shape to white background you need to fix all pixels that have a combination of white and the shape color.

What's a good way to do that?

Answer 1

It's a GIF, and is therefore in Indexed colour. You can't have semi transparency in GIFs. The format doesn't support it. You can only have either full opacity (100% solid), or full transparency.

A workaround:

If you have edges with semi transparency/anti-aliasing, when converting to Indexed mode or exporting as GIF, some raster image editors have a setting called a "matte" or "matting" which can be used to fill these outer pixels with a colour to match a background colour on a web page.

Sorry I'm not a Paint.NET user and don't know if has this feature.

Photoshop can create a matte when exporting as GIF, and GIMP can do it too, where it can be achieved using the "semi-flatten" filter on each layer before exporting as GIF.