Convert x3f to dds Online: x3f2dds

You can use Tom's Editor to easily convert images from
Sigma Camera RAW Picture File .X3F to Direct Show Surface .DDS.
Tom's Editor is a free, online image manipulation and converter program.

Go to Tom's Editor

X3F

Sigma Camera RAW Picture File is an image format with extension X3F.

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.