Printing is one place where a larger picture can really make a difference. And in online art galleries like the one I run, very often large works with a lot of detail need more pixels to see detail properly.
Well, if you’re on a Mac, the venerable Graphic Converter will batch-process entire folders’ worth of files, reducing filesize to a specified parameter, converting TIFFS to JPEGs, optimize colors for the web, etc etc.
High-end graphics shops use Photoshop in conjunction with AppleScript to do batch-processing, but GraphicConverter will do the job for most mortals.
Since no one else has mentioned it, let me put in a plug for Graphic Workshop Professional. Their latest (unregistered) version puts a watermark on images you manipulate with it, but the registration fee is only $30. GWSP will let you convert from pretty much any format to any other with complete control over quality and size. It does batch processing, special effects, thumbnail catalogs, proof sheets, etc. very quickly and easily. Also, the company that produces GWSP, Alchemy Mindworks, is from Canada and seems to have an interesting world-view (judging from their promotional materials). I’ve been using Graphic Workshop for at least 15 years, and I haven’t had a single complaint with their software.
btw, this is not a paid promotion, I just like their stuff.
MSPaint uses nearest neighbour interpolation when resizing pics which produces horrible image quality. Photoshop is likley to use Bilinear or Bicubic which gives you a much nicer pic for a given reduction.