I'm exporting from iphoto on a Mac; I just can't get originally sharp photos to stay sharp for the gallery when I reduce file size to gallery requirements unless I am exporting a severely cropped photo (where file size is already reduced).... if you know how to do this please let me know.
You've spotted something alot of people miss: photos reduced for online viewing aren't quite as sharp or sometimes develop rough edges. There are a few factors at play:
- The JPEG file format is "lossy" and induces blur by it's very nature.
- If you upload something higher-res than 1024x900 for the Gallery, the system is down-rez'ing it for you. Even software as good as Photoshop isn't perfect at this, I just expect even less for a social platform (as Tumblr always reminds me, it's truly horrible there).
- Even if you carefully down-rez your own photos, the act of doing so induces a small amount of blur by it's very nature.
So your first line of defense is to downsize it yourself. As others have noted, don't downsize your only copy. Keep a high-res for yourself and create a downsized copy; that's what I do.
Second line of defense is to sharpen the image after you downsize it. But for goodness sake, if you have access to decent software don't simply use the Sharpen command: use Unsharp Mask or Smart Sharpen. I can even recommend settings for anyone wanting to try. For advanced users you can then dip-into plugins which offer even more control (which lately I have been exploring).
Third: always over-sharpen slightly when saving to JPEG. The JPEG lossy format induces slight blur, so slightly over-sharpen to compensate. This isn't 100% necessary, but is useful to keep in mind for the detail-oriented users.
Last: if you have software that lets you control how small to make the JPEG, always adjust it so you get as close to the max. file size (500kb for the Gallery) without going over. Less compression means less data loss and less induced blur. I fine-tune every BirdForum upload's JPEG compression, which runs from 65% (lower quality) to 95% (near-original quality) depending on the photo.
Does iPhoto let you do any of this? No idea; even as a Mac user myself, I'm a design/marketing professional so I've always had Photoshop around. I hear Lightroom is also very adept at this, and I am sure there are others I am unaware of. If iPhoto cannot resize, at least offer "Unsharp Mask", and control JPEG compression amount, my advice is to find software that does within your means.