reducing ringing on text

Hi

I'm reusing book image files from archive.org for a javascript 'flippy'
book reader. The source files are large jpeg2000 files. On archive.org
itself these files are processed on the fly: reduced in size by a factor
of 4, and output as jpeg files with a quality setting of 75%. This is
done using kakadu. I'm trying to do the same thing with ImageMagick, but
offline, so I'm not concerned about processing time. The kakadu output
images are reasonable, but the images I'm getting out of ImageMagick
suffer badly from ringing (I assume it's ringing: shadow images of
vertical lines, as in 'h' or 'l' just to the left of the real line).

At the moment I'm just using

convert filename.jp2 -reduce x600 -quality 80% filename.jpeg

Is there a better way to deal with this particular type of image? I know
that the target size/quality is reasonable for the images, since kakadu
can do it.

Thanks
Graham