optimize

     set term gif animate optimize

The optimize option [DEPRECATED] is passed to the gd library when the output file is opened. It has two effects on the animation.

1) A single color map is used for the entire animation. This requires that all colors used in any frame of the animation are already defined in the first frame.

2) If possible, only the portions of a frame that differ from the previous frame are stored in the animation file. This space saving may not be possible if the animation uses transparency.

Both of these optimizations are intended to produce a smaller output file, but the decrease in size is probably only significant for long animations. Caveat: The implementation of optimization in libgd is known to be buggy. Therefore use of this option in gnuplot is not recommended.