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Creating images

Images can be created using many different tools and methods. The more conventional ways include the use of software such as drawing, CAD, graphics, presentation and graphing packages. It is also possible to have photographic negatives or transparencies transferred to Photo CD and then convert the images to an appropriate file format. Input from scanners, digital cameras and fax modems can also be treated in this manner. Screen capture software can be used to make images directly from the computer screen, as has been done for this book.

Although many different graphics file formats exist, most browsers will only cope with a few. In practice the only format common to all browsers is GIF, a widely used format devised by CompuServe. While this is currently the most commonly used format on the Web, other graphics file formats have their strengths and some look set to increase in popularity. Browsers that can display images in other formats, primarily JPEG, are starting to appear. As yet such browsers are not in common use, but are likely to be so within the next year.

GIF is an eight-bit format, which means that it can display only 256 distinct colours, while JPEG is a 24-bit format, giving a total of 16 million colours. Of course, not all hardware can display such a colour range; low end PCs often only have a palette of four, sixteen or 256 colours, which must also be shared with other applications that are running concurrently. JPEG provides variable image compression, resulting in a file that is typically half or a third the size of the same image stored in GIF format; however, the compression algorithm is `lossy', which means that the quality of the compressed image is degraded.

At the moment it is safest to create images in GIF format to reach the widest audience, but this might change in a relatively short time.

Most packages with an image generation facility can generate files in several different graphics file formats, including GIF. If you have existing files in some other format, it is a simple matter to load them into a graphics package and save them in GIF format. If you have a large number of files to convert you will probably want to do this as a batch process - a facility provided by some image manipulation packages. Some of the most widely used commercial packages are Corel Draw, Adobe Illustrator or Aldus Freehand, available for Microsoft Windows, OS/2, Apple Macintosh and some versions of UNIX. There are also numerous shareware and public domain packages available on the Net. The most popular packages for UNIX and the X Window System are XV, ImageMagick and the PBM utilities.

Spinning the Web by Andrew Ford
© 1995 International Thomson Publishing
© 2002 Andrew Ford and Ford & Mason Ltd
Note: this HTML document was generated in December 1994 directly from the LaTeX source files using LaTeX2HTML. It was formatted into our standard page layout using the Template Toolkit. The document is mainly of historical interest as obviously many of the sites mentioned have long since disappeared.