The background color may be changed by an option. The input files may be in either GIF87a or GIF89a format. If a GIF file contains more than one image, only the first image is read. To help saving bandwidth on the internet, there are options for forcing all GIFs in the series to use the same color map and to create sub-GIFs which only give the difference between one image and the next.
Output is written to the error out file.
This is a global option and must be given before any GIFfiles. When this option is used as a file-option, its setting is valid for all subsequent GIFfiles, until it is used again. Set the color identified with its index to be the background color, possibly overriding the background color defined in the first GIFfile. This is a global option and must be given before any GIFfiles. Whenever a value of delay is set by means of the -time option, this value will be valid for the following GIFfiles until a new value is set.