Raster and Vector Images and the Different Raster File Formats



Raster and Vector Images and Their Various File Formats

By: Virgil McDonald

Raster and Vector Images and Their Various File Formats

Raster and vector images are the most commonly used images in web page design today. They consist of many different file formats ranging from common jpeg files used primarily for photographs to bitmap (.bmp) files for other uses. So, what are they? The definition of a raster image is an image that is made up of small computer pixels (small squares). A raster image is also specified by three 8-bit color values defining the amount of green, blue, and red in each pixel. A vector image, on the other hand, is an image that defines curves and lines using various mathematical formulas. Using this mathematical precision, one can easily scale the image to a smaller or larger size without the loss of quality in the picture. Raster and vector images and their file formats are very important in the building of a personal or business webpage on the Internet today and, with the development of new improved file formats, they will surely be used far into the future.

One may ask then, “When are vector images used in a webpage?” They are commonly used when an image needs the ability to be resized without a change in picture quality. One would also use vector images to record images descriptively. These images are also easy to modify. The components of the vector image can be moved, resized, rotated, or deleted independently allowing for great flexibility of use. A couple examples of vector images being used in the United States are the vector graphics display in the US SAGE air defense system and the TX-2 at the MIT Lincoln Laboratory to run the program Sketchpad created by Ivan Sutherland in 1963. Another example of a use of vector graphics was the original home gaming system called Vectrex and old arcade games such as Asteroids and Space Wars. More recently, vector graphics have been used mainly for 2-Dimensional computer graphics for technical drawings and 3D renderings such as in AutoCAD and the like.

Though not as extensive as raster file formats, there are many different vector file formats. Some of them are XML, GXL, SVG, and WMF. First, XML (Extensible Markup Language) is a general purpose markup language. Many other vector formats are based on XML. Its main purpose is to incorporate the sharing of data across different information systems. GXL (Graph eXchange Language) is an XML sublanguage designed as a standard exchange file format for different graphs. SVG (Scalable Vector Graphics) is a new XML-based format for describing 2-Dimensional graphics and graphical applications in XML. Lastly, WMF stands for Windows Metafile and is a vector graphics file format used on Microsoft Windows systems that works to restore an image by storing a list of function calls that have been issued to the Windows graphic layer. WMF was used more commonly in the early 1990’s but has been displaced a bit by newer graphic formats.

As stated earlier, raster images and file formats are much more extensive then those of the vector graphics. Some of the more popular raster file formats I will discuss are the JPEG, GIF, PNG, BMP, and TIFF file formats. The most common of these are the JPEG, GIF, and PNG file formats. JPEG stands for Joint Photographic Experts Group and is a “lossy” compression format designed for compressing either full-color or gray-scale images of natural, real-world scenes. The GIF (Graphics Interchange Format) format is a lossless compression format best suited for use with cartoons, line art, or computer-generated graphics with large areas of flat color. The PNG (Portable Network Graphics) format is a derivation and improvement of the original GIF format which is also lossless and, thus, similar to the GIF format. These three formats are very simple to understand and use for the general public. They are seen in most websites with pictures and are some of the file formats with the highest picture quality and ability to be resized with the least noticeable pixilation of other raster images.

Some other common raster file formats are the TIFF, PDF, and TGA formats. TIFF (Tagged Image File Format) is used widely for traditional print graphics and uses both lossy and lossless compression. Most web users are familiar with PDF files. They are used extensively in Adobe Acrobat and other similar programs. PDF stands for Portable Document Format and is a page description language allowing for files containing multiple links and pages. It is also used as the metafile format for Mac OSX. The TGA format is another useful file format. It is the native format of Truevision, Inc.’s TARGA boards. These TARGA boards were a couple of the first graphic cards used to support truecolor display for PC’s that were IBM-compatible.[1]

It may be of interest too that there are different file formats created exclusively for the type of operating system in use. A few of these are PICT, BMP, and PBM files. PICT Files are used with Macintosh computers extensively and stands for Picture files. They are thus used with mainly photographs and other real-life pictures. BMP files are used with IBM-compatible PC’s in Microsoft Windows and its programs. BMP stands for Windows Bit-Map. These files are used in many different aspects of the Windows programs including photographs, cartoon pictures, line art, and various graphic art. Lastly, PBM files are used with the old Unix systems. It is a simple black-and-white format and uses 1 bit per pixel compression.

Another concept of raster and vector images is the conversion of one to the other. This is a very common practice. I will discuss the conversion of raster images to vector images. This conversion is a relatively new technology (last 10yrs). Different companies and corporations have used this new technique especially in conjuction with CAD and GIS systems. Using a procedure commonly referred to as “Paper-to-CAD Conversion,” drawings in physical form such as papers, blueprints, and plots are converted to CAD drawings. The process is also known as “vectorization,” the conversion of raster images to vector images. Another result of “vectorization” can be the incorporation of a photograph or raster image in a geometric design.[2]

Whether converting raster images to vector ones or just using the individual file formats of either, the different raster and vector images are now and will be important in the future of webpage design. Vector images have been used in our early military systems, early arcade games, and geometric designs. Raster images have been used in just about everything else. Neither is more pertinent than the other. They may, however, be going in slightly different directions. More recently, raster images are moving towards a more artistic and photographic scene while vector images are moving towards use in science and technology.

Works Cited

Anderson, Ruth Ann. Exploring the Art and Technology of Web Design. Clifton Park: Thomson Delmar Learning, 2006.

Digital Imaging Part 1- The Differences in Raster and Vector Images. Reed, Stacey. 25 April 2006. 13 November 2006. .

Multimedia File Formats Guide. The Fondren Library at Rice University. 13 November 2006. .

Raster Graphics. Wikipedia trademark of Wikimedia Foundation, Inc. 13 November 2006. .

Raster Image Files. Boston University. 13 November 2006. .

Vector Graphics. Wikipedia trademark of Wikimedia Foundation, Inc. 13 November 2006. .

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[1] Graphics File Format Summary. Wikipedia trademark of Wikimedia, Inc. 2006. .

[2] Raster to Vector. Wikipedia trademark of Wikimedia, Inc. 2006. .

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