CALS raster

CALS raster is a collection of image file formats developed by the U.S. Department of Defense as part of the CALS initiative.

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 (Type 1 and Type 2), and two more that have also been placed under the CALS umbrella.

Type 1

 * 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 Application Profile (DAP)
 * Filename extension: .ct2

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

Type 3

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

Refer to NIFF (Navy Image File Format).

Type 4

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

Refer to JEDMICS C4.

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

Specifications

 * MIL-PRF-28002C: CALS raster; defines Type 1, 3, and 4.
 * FIPS PUB 194: Type 2
 * MIL-STD-1840C: CALS

Software

 * ImageMagick
 * Konvertor
 * XnView

Sample files

 * https://telparia.com/fileFormatSamples/image/cals/

Resources

 * Tiled Raster Graphics and MIL-R-28002A: A Tutorial and Implementation Guide (Type 1 and 2)
 * , from the Encyclopedia of Graphics File Formats
 * Wikipedia article