which base plug-in for a Photoshop scaling filter

Hello,

I'm looking at the documentation and samples for the Photoshop SDK, but I can't find which type of plug-in I should use so I can create a resizer plugin with custom upscale/downscale.  So far it seems like the output of the filter (or other plugin) has to be the same horizontal and vertical resolution as the input.

Thank you for the help!