GIFs at Vancouver Webpages

November 1999

Unisys holds a patent on the LZW compression algorithm used in GIF images. Recently, Unisys' licensing policy on OpenSource software and shareware was changed to require a license for all use of LZW products, particularly on the Web.

Vancouver Webpages uses OpenSource software under Linux exclusively, and the Site License offered by Unisys does not justify its cost to us, so most GIF images generated here are being replaced by PNG or JPEG.

Vancouver Webpages supports some GIF advertising banners and logos. Some of these are hosted elsewhere and are not our responsibility. Others were generated elsewhere and copied here. As far as we are aware, these GIFs were generated using commercial software. Unisys' position on commercial software is unclear, but it seems that some, if not most, commercial software is licensed to generate Web images.
If it can be shown that this is not the case, such images will be removed or replaced by PNG or JPEG images.

At this time, PNG does not support animations. One or two animated GIFs still exist on the site. As far as I can determine, these were generated using opensource libraries from which LZW compression algorithms have been removed. When an alternate animation scheme is available, these will be replaced.

Currently, Web browsers commonly support four types of inline image:

In some cases, external compression may be supported: * This GIF does not use LZW compression. Using LZW, it would be 147 bytes.

PNG (Portable Network Graphics) are supported in newer browsers including Netscape and Internet Explorer, and are thus accessible to the majority of users. Certain older browsers such as Mosaic will be unable to display PNG images, and in some cases JPEG images. Our apologies for the inconvenience.

For more information and links to Unisys, PNG software etc. please see

If you need some images available in JPEG or XBM rather than PNG, please ask.