I have done some work to improve and extend the command-line options in batch processing mode, and wrote a rather extensive blog post that explains all the details.
The rearrangement and update of the command-line options was motivated by the fact that up to now it was not possible to specify the image export parameters (format, bit-depth, output colorspace, image size, port-resize sharpening, etc…) in batch mode.
Now this is fixed in the stable branch, and new packages are available for download.
Among other things, PhotoFlow can now be used as an alternative for high-quality image resizing. All resizing operations are performed on linear-gamma data in 32-bit floating-point precision, using the default high-quality algorithm of the VIPS library.
You can read more and get all the useful details in this blog post.