Transparency is the reason to pick APNG
Leave Keep transparency ticked and any alpha in your source images carries straight through to the animation — a spinner or icon will sit on a dark page as happily as a light one. GIF cannot do this: each pixel is either fully opaque or fully clear, so anti-aliased edges pick up a halo of whatever colour they were flattened against.
Untick it if you would rather flatten onto white, which usually makes the file smaller.
Mixed image sizes
Every frame of an APNG shares one header, so they must all be the same size. Images that do not match the first one are scaled to fit and centred rather than stretched, which keeps their proportions intact. For a predictable result, export your frames at one size before you start.
APNG versus GIF
GIF is limited to 256 colours per frame and its transparency is a single on/off bit, which is why gradients band and edges look ragged. APNG is a PNG that moves: 16 million colours and a full alpha channel, so soft shadows and anti-aliased edges stay clean over any background.
The trade is size. PNG compression is lossless, so an APNG of photographic video is usually larger than the equivalent GIF. It shines on screen recordings, UI demos, line art and logos — anything with flat colour and sharp edges.
Frequently asked questions
In what order are the frames used?
The order shown in the list, which starts as the order you added them. Use the arrows to move any frame up or down before you build.
Can I give each frame a different duration?
Not here — one delay applies to every frame. For uneven timing, repeat a frame in the list to hold it on screen longer.
Is my file uploaded?
No. Frames are read and the APNG is written by JavaScript in your browser — the file never leaves your device.
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