IT

COMMON GRAPHIC FILE TYPES

A file format is the way of storing information in a file so that a program can open and save the file. A file’s structure defines how it is stored and displayed. File format is indicated by a three-letter extension after the file name, such as .doc.

In making documents using the Word, many popular graphic file formats can be inserted directly into the document, eliminating the need for a separate graphic filter. The following formats are the basic graphic file types that do not need a graphic filter.

Enhanced Metafile (.emf)

Enhanced Metafile is a recently developed graphic file which is based on the older Windows Metafile (.wmf).

Graphics Interchange Format (.gif)

The Graphic Interchange Format (GIF), a compression technique developed by Compuserve, is best for images with solid areas of color; line drawings or logos; transparency effects in which you designate part of the image to disappear into the background; and animation.

GIF works by compressing blocks of color. However, GIFs can only display a maximum of 256 colors which is represented by what is called bit depth. Bit depth controls the size of the colour palette which is used to describe the image.

1 bit = 2 colours    (21 = 2)
2 bit = 4 colours    (22 = 4)
3 bit = 8 colours    (23 = 8)
4 bit = 16 colours  (24 = 16)
5 bit = 32 colours  (25 = 32)
6 bit = 64 colours  (26 = 64)
7 bit = 128 colours (27 = 128)
8 bit = 256 colours (28 = 256)

Joint Photographic Experts Group (.jpeg or .jpg)

Joint Photographic Experts Group (JPEG) was designed to compress high-quality images such as photographs and detailed artworks without sacrificing for the quality. It handles subtle shadings and color blends more efficiently than GIF.

When saving images, the amount of compression and the resulting file size can be controlled by trying on and experimenting with the different settings until the right balance of quality and size are obtained. For a rule of thumb, consider that a 36K image will take 5 seconds or longer to be downloaded on a 56.6K modem.

If JPEG is used in creating a background image for a web page, the lowest quality setting is used to get a small file size. This allows the background to be downloaded first before the rest of the page content.

Portable Network Graphics (.png)

Portable Network Graphics (PNG) is graphic format designed considered as the successor of GIF. It features compression, transparency, and progressive loading, like GIF, but it is free of patent restrictions and is supported by most current browsers even those browsers that are used in 1997. If you see the graphic above at the right, your browser supports it. Current versions of Netscape and MSIE support it.

PNG is used for lossless compression and for displaying images on the web. The advantage of PNG is that it supports images with millions of colors and produces background transparency without jagged edges. The disadvantages are that PNG images will not show up on older browsers and is still comparatively larger in file size than GIFs.

Microsoft Windows Bitmap (.bmp, .rle, .dib)

The .bmp file format is a fairly simple bitmap format that can be viewed on many different platforms but is directly supported by very few browsers. It is not commonly used on the web (fortunately, as it is very inefficient) as GIFs, JPEGs, PNGs, and X-bitmaps are more preferred as they are more portable than .bmp. this file format is somewhat similar to the pict format.

Run-Length-Encoding (.rle) is the non-lossy compression algorithm, usually compressed no more than 2:1 and is most often used on Windows *.bmp files. RLE non-lossy compressions are commonly used in archiving image files that cannot sustain any loss in quality.

Windows defined image format specification (.dib) is called device-independent because of its straightforward, common-denominator, format. It has all the information that a basic digital image needs and is laid out in a simple specification that is easy to get with. Its simplicity makes it an ideal format for holding images that need to be shared by several programs.

Windows Metafile Graphics (.wmf)

Windows Metafile (WMF) is an image file format that is used to facilitate the exchange of graphic information between applications in the Microsoft Windows operating system. The WMF format is capable of storing a decent looking screen image and the complete vector data (precise mathematical definition) of a file. So far, WMF, has not yet gained the universal support among Windows applications that Microsoft was originally aiming for, but never bet against Microsoft.

Windows Metafile format, which is an intermediate vector format for Windows programs is use when interchanging data and, generally speaking,can never be seen anywhere else.

Tagged Image File Format (.TIFF more commonly .tif)

Tagged Image File Format (TIFF) is a common format used for exchanging raster (bitmapped) images between application programs. Usually identified with the “.tiff” or “.tif” filename extension, the format was developed in 1986 by an industry committee chaired by the Aldus Corporation (now part of Adobe). Microsoft and Hewlett-Packard were also on the committee. One of the more common image formats, TIFFs are common in desktop publishing, faxing, and medical imaging applications. The TIFF file type is also commonly known as the ‘lossless, high quality’ option in digital cameras.

Encapsulated PostScript (.eps)

A file format for graphics and text supported by several graphics drawing applications, an Encapsulated PostScript (EPS) file can contain two versions of an image: a bitmap used to display the image on the screen and a PostScriptTM description used to print the image.

 

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