Convert AVIF to PNG

What a lossless target does and does not give you

Lossless means lossless from here on, not retroactively. The AVIF's compression — AV1 intra-frame coding, usually with chroma stored at quarter resolution — was applied when the file was made, and the decoder hands over the result of it. The PNG preserves that result exactly, including the soft gradients AV1 is good at and the slight smearing of fine texture it is prone to. The gain is that every edit and every save after this costs nothing further.

The alpha channel is the real reason to pick PNG over JPG here. AVIF stores transparency as a separate plane and PNG stores it per pixel; both are full 8-bit, so a soft shadow or a feathered edge survives with its gradient intact rather than being flattened onto a colour. A picture with no transparency gets an opaque PNG and the alpha channel is simply omitted.

Bit depth is where something is lost. AVIF can carry 10- or 12-bit colour and a wide gamut; the PNG written here is 8-bit sRGB, so an HDR image is tone-mapped down — a sunset that glowed on an HDR display comes out flat and no editing recovers it. Images that were 8-bit sRGB to begin with, which is nearly all of them on the web, come across without change.

When you want something else

avifdec in.avif out.png is the reference decoder and the right tool for a folder; it can also keep 16-bit output for HDR sources, which nothing in a browser canvas can. If the destination can read AVIF at all, do not convert: the original is smaller, higher quality and carries the colour the PNG cannot.

A PNG straight out of a decoder is not a small PNG. If the file is going on a website, run it through oxipng or zopflipng afterwards — they recompress without touching a pixel and routinely save a fifth of the size — or consider whether WebP lossless would serve the same purpose at half the bytes.