The buffer can be reset to an empty frame, left unmodified, or restored to the beginning of the previous frame.One of the primate goals of APNG was to introduce an animated image format that supported 24-bit color with an 8-bit alpha channels.A program the does not support APNG will display only the first frame, while an APNG-aware program will display only the second frame.
A number of demos to show off some of the things that can be done with APNGs.
APNG is designed to be backwards-compatible with image viewers which only support PNG.
Older image viewers will simply disply the first frame of the animation, like a normal image.
A flag can be set to make APNG-aware viewers ignore the first frame, so that it can be used as a staic representation of the animation. The first has "APNG not supported" text, and the second has "APNG is supported" text.
It was made by Klowner (/ dugnet.com/klown), who graciously provided PNGs from the original rendering so I could assemble an APNG version.
You can see that the APNG animation, on the bottom, doesn't have a halo effect on non-white backgrounds.