vips (available on the Linux command line) can create Zoomify tilesets like this:

vips dzsave clean_C1.png clean_C1 --layout zoomify --suffix .png

As far as we can tell, these are identical to those created by Zoomify (and we got the same number of tile groups folders using vips as we did with Zoomify).

We actually need JPEGs because OpenLayers can't yet handle PNGs, so we've determined that this is what we want for tiling (assuming that we want full-quality images).

 vips dzsave img.jpg img --layout zoomify --suffix .jpg[Q=100]