I’m no kind of artist and Photoshop is way more than I need. I’m looking for some simple and hopefully simple to learn freeware so I can experiment with different filters and mess around with color values in photographs–I’m trying to work out an idea I have so I can communicate it more effectively to the talented people who will actually do the work.
Paint.net is simple to figure out, if GIMP doesn’t look good. It doesn’t have a lot of pre-built filters, but it does give decent controls of color values for being free,
Paint.net is definitely the easiest to use of the bunch. Otherwise you can just upload them to Google Photos, Instacrap, etc. and use the filters there.
Paint.net fits your needs best, but you’ll probably want to add some plugins for the filters you want. They’re free too, just make sure you get them from the official site.
I still use Paint Shop Pro 4.12 before turning to more powerful, complicated programs. That version is 20 years old (and I’ve been using PSP since before 4.12 came out.) Google and you’ll find it on abandonware sites. It supports plug-in filters, so google for free Photoshop filters (or free Photoshop plugins) and you’ll find lots of those, too.