Convert hpm to dds Online: hpm2dds
You can use Tom's Editor to easily convert images from
Grass' Slideshow .HPM to Direct Show Surface
Tom's Editor is a free, online image manipulation and converter program.
Go to Tom's Editor
Grass' Slideshow is an image format with extension HPM.
DDS are files invented by Microsoft to be used in games, mostly as textures. Images can be compressed to save space but the compression methods defined by DDS are all very fast in terms of coding and decoding.