hmm, it never occurred to me that the thumbnails don ´t look good, especially if you turn up the quality. We are using a PHP library for resizing, and I would need to check all the functions with my partner to see if there are other options in the resizing except for quality. I know for sure there isnt a specific function for "sharpen", but there are functions for:
imageantialias(on/off),
imagecopyresampled and
imagecopyresized. (Taken from
http://th.php.net/manual/en/book.image.php )
I can ´t immediately see that any change in the settings above would help. If you turn of antialias, thumbs will look very pixelated.