C4 File

Files with the extension .C4, also referred to as CALS Raster Type 4, are predominantly used to store compressed raster images from the JEDMICS - Joint Engineering Data Management Information And Control System. This format is akin to TIFF 6.0 and TG4 but primarily differs in its file header. It employs CCITT Group 4 encoding for pixel layout representation. The files contain solely black and white images, without the capability to store colors or grayscale images.

.C4 Image Files - Data Structure

Every file with the extension .C4 begins with a 128-byte header containing metadata. The image recording - pixel information is stored as 512 x 512 pixel packets, known as tiles. The compressed image structure is as follows:

1. File header.
2. Index of "tiles".
3. Compressed image data.
4. Index for preview.
5. Preview of compressed image data.

Each header field is precisely defined, with unused ones being filled with zeros.

Utilization of .C4 Extension Files

Originally, the C4 file format was developed by the United States Department of Defense for exchanging simple graphic data. They were used, for example, to save technical drawings, as well as pages of Tech Data Package - TDP documents. Files with the .C4 specification are publically available. Nowadays, this graphic file format is mostly considered outdated. It is supported by the viewer XnView.