There are at least two rarely-used methods that can generate a GIF
that, if decoded according to the GIF89a standard, will produce an
animation that ends with a 24-bit RGB truecolor image.
GIF89a was designed based on the principle of rendering images (known
as frames when used for animation) to a logical, fixed-size screen.
Each image could optionally have no delay after it is rendered, and
could have its own 256-color palette. Also, each image need not fill
the entire logical screen, and the animation can cease after the last
frame; it need not begin again. The multi-frame, zero-delay, and
unique-palette features, optionally combined with transparency, allow
for each image to replace only a portion of the previous image's pixel
data. When used without looping, a more-than-256-color final result
can be achieved.
For example, a GIF can be encoded to render as a series of overlapping
full-screen images, each image filling in color that wasn't in the
previous one. Transparent pixels can be used to preserve colors from
previous images.
A similar method that does not use transparency is to encode the GIF
to render as a series of less-than-full-screen images adjacent to each
other, rather than overlapping.
