More below, but mainly I wonder how people here do downsizing of JPEG 
images for the web, so I'm putting this question up front:  Can any of you 
do better downsizing than this, and if so how?...

http://taxa.epi.umn.edu/~mbmiller/pics/20080701_Adriana/comparison/

The filenames reveal which program was used to downsize and to what width. 
Use the "original.jpg" with your system and see how it looks, but if yours 
looks better, make sure the downsized file is about the same number of 
bytes as mine, or smaller.  --Mike

   ---

For years I've been using an "action" I made in Photoshop to make smaller 
versions of my large JPEG photos.  For every JPEG file in a directory, the 
action would make a JPEG 640 pixels wide and another 320 pixels wide 
(maintaining aspect ratio).  It had to put them in the same fixed location 
so I had another script to move them to where I wanted them.

Now, finally, I tried ImageMagick' "convert" program on an Ubuntu machine. 
It didn't take too long to figure out how it worked.  The first few 
downsized files I made were vastly superior to what I was getting from 
Photoshop, but then I realized that my file sizes were larger -- more than 
double the size of the Photoshop files. So I read a little more about 
convert's -strip and -quality options and I titrated -quality so that I 
was getting the same filesize as Photoshop was producing.  These are the 
commands I was then using for 320 and 640 pixel wide images:

convert infile.jpg -strip -quality 80 -resize 320 -filter Lanczos -sharpen 0x0.7 outfile.jpg
convert infile.jpg -strip -quality 80 -resize 640 -filter Lanczos -sharpen 0x0.7 outfile.jpg

Here is an example of ImageMagick and Photoshop downsized output files 
along with the original:

http://taxa.epi.umn.edu/~mbmiller/pics/20080701_Adriana/comparison/

If you can do better, let me know because I will love to see your output 
files and your method (just make sure your output file size is almost the 
same as mine).

Now that the files were the same size, I still liked the ImageMagick files 
better than the Photoshop files!  That was a nice surprise.  The truth may 
be that Photoshop is better at this but I wasn't doing everything I could 
to optimize its output.  The reason is I didn't try harder is that it is a 
pain to work with the Photoshop "actions" -- I don't want to mess with 
them. ImageMagick uses command-line arguments instead of "actions" so it 
is a piece of cake to make changes to settings.  This also makes it easy 
to do scripting.  Here's what I'll be doing in bash:

mkdir 640 320
for file in $(\ls -1 *.jpg) ; do
    for N in 640 320 ; do
       convert $file -strip -quality 80 -resize ${N} -filter Lanczos -sharpen 0x0.7 ${N}/$file
    done
done

By the way, I got some of my ideas from here:

http://www.xs4all.nl/~bvdwolf/main/foto/down_sample/example1.htm

But that guy used Photoshop to "sharpen" his ImageMagick output file, 
which seems like cheating to me, or at least it confuses readers who want 
to compare the programs.  Maybe ImageMagick didn't have -sharpen back in 
2004 when he made that page.

Best,
Mike