Wikimedia Bugzilla is closed!

what software does flickr use for thumbnailing? MediaWiki generally is
configured to use ImageMagick.

By amazing coincidence, the sharper version is also twice the file 
size, and thus twice the download time and twice the bandwidth cost.

Sorry, Brion, the size has little to do with sharpness in this case.

I compressed the flickr image to have the same size as the wikimedia one:

http://img223.imageshack.us/img223/5092/graf7lc.jpg

Your personal preference for artificially sharpened images is 
appreciated, but not particularly relevant.

Perhaps the could be a configuration setting for the thumbnailing method and
quality used with ImageMagick. I don't think it needs to be changed for
Wikimedia projects, though.

Daniel, it looks clearly like a sharpen filter to me. IMHO this 
tends to increase ugliness from artifacting, but perhaps there are 
some tradeoff improvements that could be made.

I'll go ahead and reopen this if some better techniques can be 
suggested; note that a trickier thing is handling smooth areas of 
images properly. Particularly subject to ugly artifacts are areas 
such as deep blue skies and the edges of buildings against them. 
Sharpening an already JPEG'd image might make these areas worse, 
especially if quality has to be turned down to make up for the 
extra space required by higher frequency sharpened parts of the 
image.