APNG to JXL Converter

Encoding: the APNG uses lossless DEFLATE per frame, like PNG; JXL uses lossy VarDCT or lossless modular coding; existing JPEGs can be repacked without loss, and the download is a JPEG XL encoded with libjxl compiled to WebAssembly, lossy at the quality you choose or lossless.

Bit depth: 8 bits per channel in the APNG; JXL allows 8 to 16 bits per channel, or floating point, and the JXL written here has 8 bits per channel.

Colour: RGB or an indexed palette in the APNG; JXL supports sRGB, Display P3, linear and other spaces described in the codestream, written here as 8-bit sRGB.

Transparency: the APNG stores it as full alpha on every frame; the JXL keeps it as an extra channel in the codestream.

Animation: fcTL frame-control chunks with fdAT frame data after the first image; the JXL holds one image, so only the first frame is converted.

Metadata: the APNG can carry the same text and ICC chunks as PNG; JXL can carry EXIF and XMP boxes in the container form, often stripped by encoders, but nothing is copied across.

APNG extends PNG with animation frames. Unlike GIF it keeps full 24-bit colour and smooth 8-bit transparency, at the cost of larger files.

An APNG is a valid PNG with an acTL chunk announcing the frame count and loop count; each later frame is an fcTL chunk (size, offset, delay, blend and dispose rules) followed by fdAT data. Software that does not know APNG simply shows the first frame.

APNG files usually come from animated stickers (LINE and Discord among others), UI animations and Firefox-era web graphics.

JPEG XL is a next-generation format designed to replace JPEG. It compresses better than JPEG and WebP, supports lossless, HDR and progressive decoding, and can losslessly repack existing JPEGs.

A JPEG XL file is either a bare codestream starting with FF 0A or an ISO base media container whose 'jxlc' box holds the codestream. A recompressed JPEG keeps a 'jbrd' box that lets the original JPEG bytes be rebuilt exactly.

JXL is the better choice for archiving and future-proof high quality storage, while APNG suits high quality animated stickers and UI animations.

JXL strengths: Excellent lossy and lossless compression; Progressive decoding and HDR; Huge image sizes. Drawbacks to weigh: Browser support is limited (Safari only by default); Few apps can open it yet.