This specification is intended to be used by contracting agencies of the DoD in the procurement of raster graphics data and raster graphics applications. The specification presents raster graphics requirements which are applicable to interchange of raster encoded technical document pages, foldout illustrations, and large format engineering drawings.

Raster graphics representation specified herein consists of two types. Type I raster graphics data has a simple file format with no document architecture and is untiled (i.e., it is represented by a single compressed data entity). Type II raster graphics data has a document architecture conforming to the ODA Raster DAP (Appendix A). Type II data may be tiled and/or untiled as specified in the contract document.

Type I raster graphics requirements are intended to be used in procuring data for systems that only use untiled raster graphics representations. Examples of such systems include typical technical documentation systems and Digital Storage and Retrieval Engineering Data System (DSREDS)/ Engineering Data Computer Assisted Retrieval System (EDCARS) used by the Army and Air Force.

Type II raster graphics requirements are intended to be used in procuring data for systems that need the flexibility to use tiled or a mixture of tiled and untiled raster graphics representations. Tiled representations are best applied in systems handling large format drawings or illustrations typically associated with engineering design. The subdivision of a drawing into tiles permits use of only those portions of an image required at a given time by the application. This can result in reduced requirements for workstation memory and workstation display area. In addition, tiling permits compression and decompression activities to be performed in parallel upon the drawing tiles. Type II provides for untiled raster graphics for images considered too small to tiling (i.e., A-size or smaller).

It is the intent of this specification to use existing and emerging technology as the basis for implementation. Formats presented for Type 11 data use such technology. This ensures raster graphics specification efforts are within the mainstream of evolving raster imaging technology and promotes interoperability with other raster graphics formats used in the office document architecture standard. It is the intent of this specification to use new mechanisms or objects only where existing work cannot reasonably accommodate specification needs.

Appendix A presents the specific limits and defaults for each of the document architecture presentation and content attributes used to interchange Type II raster graphics data.

This specification exclusively requires CCITT Recommendation T.6 (Group 4) compression for Type I and Type II raster graphics encoding with a bitmap option for Type II encoding. CCITT Recommendation T.4 (Group 3),compression is specifically not supported. The uncompressed escape option defined in FIPS PUB 150 is not supported. Variations to the T.6 algorithm which are briefly mentioned in a note in FIPS PUB 150 (CCITT Recommendation T.6) are not supported.

For tiled raster graphics the ability to intersperse compressed and bitmap tiles as described by the "Tile-types" attribute in Appendix A meets several user requirements for tiled raster graphics content. A system or peripheral which must meet a given throughput requirement can selectively choose to leave uncompressed those tiles which do not compress in a specified amount of time. Similarly, this ability permits an upper bound to file size by using bitmap encoding for those tiles which (had they been compressed) would have compressed negatively. Both these requirements arise from the need to predict the behavior of an essentially statistical encoding technique.