From the same makers of the little proggy that converts dds files to useful raster formats, this is a really nice free texture tool that will produce seamless materials. It seems to automatically export 512 x 512 images…which is very nice. All sorts of controls, including how big a blend margin you want around the image.
I grabbed a stony ground texture off the net and made in seamless with just a few clicks. It’s not quite as comprehensive as some commercial programs like Texture Maker, but it gets the job done.
You can get it here.
And here’s the result in practice.