6.4a Graphic formats
GIF (Graphics Interchange Format)
GIF stands for graphics interchange format, a file format used extensively on the World Wide Web. GIF supports colour and various resolutions. It also includes data compression, but because it is limited to 256 colours, it is more effective for scanned images such as illustrations rather than colour photos. It displays quickly on browsers without needing a plug-in.
JPEG (Joint Photographic Experts Group)
It is a good format for displaying photographs, because it supports millions of colours and can be compressed quite small. JPEG provides a compression method for "continuous tone" image data with a pixel depth of 6 to 24 bits. It is possible to choose how the level of compression, however, the smaller the final file, the greater the information that is lost. Nevertheless, certain settings of JPEG compression can yield a result that appears visually similar to the original. In general, a JPEG file will compress a photographic image two to three times smaller than a GIF. Compression makes JPG files a poor choice for archiving or for when you might need the image at full quality later.
PNG (Portable Network Graphics)
PNG is a relatively new standard from the World Wide Web Consortium designed to replace the GIF format. Used to transmit and store bitmapped images, it has several advantages over GIF: variable transparency, cross-platform control of image brightness and two-dimensional interlacing. It supports 48 bit true colour or 16 bit grey-scale. It is a good choice for archiving bitmap images and is Web friendly. It compresses across rows and columns of pixels, often allowing for greater compression than GIF by 5-25 percent. This lossless compression method is fast, well documented and available at no cost.
SVG (Scalable Vector Graphics)
SVG is a new graphics file format and Web development language based on XML, which is being developed by the World Wide Web Consortium. It is a language for describing two-dimensional graphics in XML. SVG benefits from XMLs' strength and widespread use. Any existing XML parser can read SVG, making exchange easy. A major drawback to SVG is that it is not yet fully supported by any browser. Users of Web browsers must use plug-in technology, such as the Adobe SVG plug-in, to view SVG images.
TIFF (Tagged Image File Format)
TIFF is an old standard designed to store black and white images created by scanners and desktop publishing applications. Today it is probably the most versatile, widely supported, and reliable bitmap format. TIFFs' extensible nature allows it to store multiple bitmap images of any pixel depth: bitonal, grey-scale, palette colour and true colour. It is a good choice for archiving bitmap images, but not for publishing on the Web, as TIFFs can result in large file sizes. TIFF can be compressed in several ways and is not platform dependent. It can also be stored as uncompressed data, but as mentioned, the files are quite large.
EPS (Encapsulated Postscript file)
EPS is a standard format for importing and exporting PostScript language files in all environments. It is usually a single page PostScript language program that describes an illustration. The purpose of the EPS file is to be included as an illustration in other PostScript language page descriptions.
In general, a metafile is a list of commands that can be played to render a graphic. Typically, a metafile is made up of commands to draw objects such as lines, polygons and text and commands to control the style of these objects.
Microsoft Windows Metafile (WMF) is a 16 bit metafile that can be used by Windows 3.x, Windows 95, 98 and Windows XP to display a picture. A Microsoft Enhanced Windows Metafile (EMF) is a 32 bit metafile that can be used by Windows 95, 98 and XP (not Windows 3) to display a picture. It can contain a much broader variety of commands than a regular Windows metafile.