Creative Tools: IFF and the Art of Sharing

Saving a picture was only half the job. Another program still had to understand it. Electronic Arts’ 1985 IFF standard addressed a practical problem for home-computer artists: moving their work between independently developed tools.

IFF means Interchange File Format. It describes a container rather than one universal kind of picture. An image commonly uses FORM ILBM, identifying an interleaved bitmap. That distinction matters: calling every IFF file a picture is rather like calling every floppy disk a game.

The container is divided into chunks. Each starts with a four-character identifier and a 32-bit byte count. A reader can use the length to skip an unfamiliar chunk. This gives developers room to add information without automatically making older readers reject the entire file.

Inside an ILBM, BMHD describes the bitmap, CMAP carries its palette and BODY holds the image data. Keeping those roles separate preserves context that a simple screen-memory dump would leave another application to guess.

The pixels have a deliberate arrangement, too: bitplane rows are interleaved by scan line. For each line, the file stores a row from each plane before proceeding to the next line. A decoder must respect that order rather than treating the data as complete consecutive planes.

Optional ByteRun1 compression encodes repeated bytes economically, with each bitplane row packed separately. Flat areas can therefore save disk space without discarding image detail; noisy artwork may offer less to compress.

IFF’s useful achievement was a shared description of the work. The file carried enough information for another tool to do something sensible with it.

Recommended reading: For the wider history of Amiga and Atari ST productivity software, explore 68000: THE FLAME WARS.