59 CALS Compressed Bitmap Image (Raster) CAL is an image file format used by CALS. CAL files are compressed bitmap formatted files used for storing monochrome images. CAL files were developed in the 1980s to standardize graphics data interchange for electronic publishing for the federal government. Text 1 Digital Preservation Department / The National Archives 02 Aug 2005 03 Aug 2015 x-fmt/28 PUID cal File extension 343 CALS Compressed Bitmap First record identifier in the CALS Header Block: srcdocid: 1 Absolute from BOF 0 737263646F6369643A