Just published a blog post about my NES graphics tool - makechr - that I've used for my last few projects, as well as some upcoming works. The new build has a GUI frontend to complement the command-line version, and also is available as a windows exe that works with no install. I realize a lot of folk use NES Screen Tool, but I found it never quite matched my use cases. I've seen some others using ad-hoc one-off conversion scripts, but I wanted something a bit more reliable and flexible. Also, this is completely cross-platform (though the single executable version is Windows-only, it runs great in wine, and a .app is coming soon for OSX).http://www.dustmop.io/blog/2017/02/16/b ... kechr-exe/
The blog post goes through using makechr's GUI to convert a background image into CHR, nametable, etc, then how to include these files into a ca65 project. It also converts a sprite sheet into 8x16 OAM data, and renders some sprites onto the screen. Hopefully folks find it useful! There's a lot more options for makechr (the README lists them), and I anticipate writing some more about it in the future.
Source on github - https://github.com/dustmop/makechr