Convert ist to dds Online: ist2dds

You can use Tom's Editor to easily convert images from
Interlace Studio .IST to Direct Show Surface .DDS.
Tom's Editor is a free, online image manipulation and converter program.

Go to Tom's Editor

IST

Interlace Studio is an image format with extension IST.

DDS

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.