What it says in the subject. I installed Gimp 2.10 (final release) on Window 10 x64 and I'm so far unable to use the "Color to Alpha" tool -- the option is simply greyed out. And yes, the image IS in RGB mode. I tried several images, in fact. Otherwise, it seems to work fine, and I do like a number of the changes.

I even uninstalled Gimp, rebooted, deleted all GIMP-related folders (in my user profile and such) to guarantee a clean reinstall, and then reinstalled it. Same thing. I checked it first thing after rebooting (so no settings had changed), and it's still unavailable.

The funny thing is, I got the PortableApps version today and installed it in a separate folder... and this one WORKS. So it doesn't appear to be any kind of weird incompatibility with my video driver or something.

Well, at least having the PortableApps version as a fallback for whatever features don't work in the main install means that I won't have to downgrade to 2.8.22... but it's still really annoying to have a feature refusing to work.

Any thoughts?

Further testing (and a hint from another forum) revealed the root of the problem: the images didn't have an alpha channel. If I add an alpha channel (can't find a convenient one-click option for that, so I'm making do with adding a transparent layer and merging it to the main image), it works fine.

Still can't figure out why the portable version does not require this extra step. Must be something in the settings, which probably have different defaults in the portable... I'll have to dig further.

Still can't figure out why the portable version does not require this extra step. Must be something in the settings, which probably have different defaults in the portable... I'll have to dig further.

Found it! It was in the "Image Import & Export" preferences. I guess I'll have to do some more experimenting and tweaking with the settings, in order to find out what else changed from 2.8...