FTS extensions is used for files that store images in Flexible Image Transport System format. FTS files are typically used in Astronomy and for medical imagining. FTS standard was approved by NASA and IAU.

FTS were originally store on magnetic tape. FTS files are used for sharing and editing scientific images. Typical FTS files contains header section that stores file metadata in plain ASCII text. Single FTS files may contains multiple images saved in different formats. FTS files also support multidimensional tables.