CALS raster

Overview
CALS raster is a group of image file formats associated with the U.S. Department of Defense.

CALS stands for Continuous Acquisition and Life-cycle Support (new name), or Computer Aided Acquisition and Logistics Support (old name).

Format
There are two main formats, and at least two more that have also been placed under the CALS umbrella.

Type 1

 * Description: Untiled
 * Filename extension: .ct1 (MIL-PRF-28002C), .cal (MIL-PRF-28002B)

Type 1 files have a 2048-byte ASCII header, consisting of up to 16 128-byte header fields.

Bi-level image data follows, which always uses CCITT Group 4 compression.

There are two versions of Type 1 format: one defined in MIL-PRF-28002B, and one defined in MIL-PRF-28002C.

Type 2

 * Description: Office Document Architecture (ODA) Raster Document Appilcation Profile (DAP) Tiled/Untiled
 * Filename extension: .ct2

Type 2 is a more complex format, which adds support for multiple images, uncompressed images, and other things.

Type 3

 * Filename extension: .ct3, .nif
 * Description: Navy Image File Format (NIFF) Tiled/Untiled

Type 4

 * Description: JEDMICS C4 Tiled
 * Filename extension: .ct4, .c4

See JEDMICS C4.

Identification
Type 1 files most likely start with ASCII string " ", " ", or " ".

Specifications

 * MIL-STD-1840C
 * MIL-PRF-28002C

Software

 * ImageMagick
 * XnView

Resources

 * CALS Raster File Format Summary
 * Wikipedia article