CompuServe, an on-line service, developed the GIF format to provide good file compression and relatively fast decompression speed. GIF is a very popular format for online services, but is limited to a maximum of 256 colors.
Two standards have been developed: 87a and 89a. ThumbsPlus fully supports the 87a standard, and supports (for viewing) much of the 89a standard, including multiple images (GIF animations), text blocks and input extensions.
ThumbsPlus can read and write interlaced and transparent GIF files. Transparency (for a specific color) is maintained when the image is saved. Note that if you modify the colors of the image, you'll most likely need to select a new transparency color. The topic GIF Save Options ontains more information on saving GIF files.
ThumbsPlus cannot create or modify multiple-image GIF files, or GIF files with text or input extensions; only single-image GIF files can be written.