.c16 is the extension for C16 files, used in most Creatures 3/Docking Station images. These files actually store several images, so most agents only need one c16. They can be viewed and edited with Creature Labs' SpriteBuilder, and previewed in Windows using GreenReaper's Sprite Thumbnail Viewer. The c16 is a compressed version of the s16 file, where transparent pixels are grouped together as a pixel count. C16 files are used by the Creatures Evolution Engine to store compressed sprite data. They're compressed simply by Run Length Encoding (RLE) transparent pixels in the image files.