Appendix B
Communique! Supported Graphics File Formats
Communique! tools support a wide variety of graphics file formats for loading and saving images. By supporting most of the popular file formats, Communique! tools can work seamlessly with many different applications, operating systems, and computing platforms. If you are unfamiliar with some of the formats supported by Communique! tools, this section will briefly explain each of them.
Windows Bitmap (BMP)
The Microsoft Windows Bitmap (BMP) format is used primarily on MS-DOS, Microsoft Windows, and Windows NT platforms. Most applications running on PCs support the Windows Bitmap format. It can store images with up to a 24-bit color images (16.7 million colors). Communique! uses the simplest, uncompressed form of Windows Bitmap to ensure compatibility with other applications. This form is very fast to decode but can produce files of considerable size, especially for 24-bit images.
GIF
The GIF format was created by Compuserve and is now one of the single most popular image formats available. Most PC, Macintosh, and UNIX programs that read and write graphics data support the GIF format. One of the limitations of the GIF format is that it can only save up to 8-bit images (256 colors). If you save a 24-bit image into the GIF format, the image will be dithered down to an 8-bit image with 256 colors. GIF uses a moderate, lossless compression scheme that produces files much smaller then Windows BMP, but in most cases larger than files created by the JPEG file format.
JPEG/JFIF
JPEG or JFIF files use the JPEG compression algorithm developed by the Joint Photographic Experts Group. The JPEG file format is not as widely supported as GIF and TIFF, but it is becoming more popular. The JPEG format can store up to a full 24-bits of color (16.7 million colors). The main benefit of JPEG is its incredible compression levels. There are two drawbacks to using the JPEG format to save your files, however. The first is that JPEG, unlike the other formats supported by Communique!, employs lossy compression. This means that to achieve its dramatic compression level, JPEG must actually remove image data which may result in a slight decrease in image clarity. This loss in quality is usually not noticeable, especially when saving photographic or real world images, but you will probably not want to use JPEG for images containing fine details that will be lost through compression. The second drawback to JPEG is speed. JPEG files will take longer to load and save than with other formats. This delay may become an issue if you are using a relatively slow computer or are working with large image sizes.
PCX
The PCX format developed by ZSoft is used primarily on MS-DOS, Microsoft Windows, and Windows NT platforms. Most applications running on PCs support the PCX format. It can store up to 24-bit color images (16.7 million colors). It employs a simple, lossless compression scheme that is very fast to decode but can produce files of considerable size, especially for 24-bit images.
Sun Raster
The Sun Raster format is used primarily on Sun Microsystems UNIX workstations. Most applications running on Sun machines, and many on other UNIX platforms, support the Sun Raster format; but PC and Macintosh applications are unlikely to support it. The Sun Raster format can store up to 24-bits color images (16.7 million colors). Communique! uses the simplest form of Sun Raster file compression to assure compatibility with other applications. This form employs a simple, lossless run length encoded compression scheme which is very fast to decode but can produce files of considerable size, especially for 24-bit images.
TARGA
The Targa (or TGA) format is used primarily on MS-DOS, Microsoft Windows, and Windows NT platforms. The Targa format is supported mainly by high end graphics applications, especially those packages dealing with scanners, frame grabbers, and ray tracing. The Targa format can store up to 32-bit color images. It employs a simple, lossless run length encoded compression scheme that is very fast to decode but can produce files of considerable size, especially for 24-bit images.
TIFF
The TIFF format is used primarily on MS-DOS, Microsoft Windows, Windows NT, and Macintosh platforms. Most applications running on PCs and Macintoshes will support the TIFF format. It can store up to 24-bit color images (16.7 million colors). Communique! uses the simplest form of TIFF file compression to assure compatibility with other applications. This form employs a simple, lossless compression scheme that is very fast to decode but can produce files of considerable size, especially for 24-bit images.
XWD (Read Only)
The X Window Dump (XWD) format is used by UNIX workstations running X Windows. Communique! does not write files in the XWD format, will read XWD files created by other applications, such as the UNIX command xwd.
Encapsulated PS (Save Only)
The Encapsulated PostScript format (EPS) is not like other image formats supported by Communique! in that it is a save only format. EPS files are generally not a bitmapped image format, and cannot be loaded in as images the way other formats can. EPS files are a special subset of PostScript files that can be used within a PostScript document. Most desktop publishing packages on PCs, Macintoshes, and UNIX workstations will allow you to insert EPS images in their documents.