GIF to JXL Converter

Encoding: the GIF uses lossless LZW over a palette of at most 256 colours; 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 pixel, as indexes into a palette in the GIF; JXL allows 8 to 16 bits per channel, or floating point, and the JXL written here has 8 bits per channel.

Colour: an indexed palette of up to 256 colours per frame in the GIF; JXL supports sRGB, Display P3, linear and other spaces described in the codestream, written here as 8-bit sRGB.

Transparency: the GIF stores it as one palette entry marked transparent, so each pixel is either fully shown or fully hidden; the JXL keeps it as an extra channel in the codestream.

Animation: image blocks with their own delay and disposal method, looped by the NETSCAPE2.0 extension; the JXL holds one image, so only the first frame is converted.

Metadata: the GIF can carry comment and application extension blocks, but no EXIF; JXL can carry EXIF and XMP boxes in the container form, often stripped by encoders, but nothing is copied across.

GIF is the classic animated image format. It is limited to 256 colours per frame and 1-bit transparency, so photos look grainy and files are large, but it plays everywhere.

A GIF starts with 'GIF89a' (or the older 87a), a logical screen descriptor and an optional global colour table, then image blocks, each preceded by a graphic control extension that sets its delay and transparent colour.

GIF files usually come from reaction clips, memes, old websites and screen recordings.

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 GIF suits short animations and reactions that must play everywhere.

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.