Free Lossless Image Format

Free Lossless Image Format

Filename extension	.flif
Internet media type	image/flif
Uniform Type Identifier (UTI)	public.flif
Magic number	FLIF
Initial release	3 October 2015 (2015-10-03)[1]
Latest release	0.3 (28 April 2017 (2017-04-28)[2])
Open format?	Yes
Website	flif.info

Free Lossless Image Format (FLIF) is a lossless image format (current version FLIF16 specification) claiming to outperform PNG, lossless WebP, lossless BPG and lossless JPEG 2000 in terms of compression ratio on a variety of inputs.^[3]

FLIF supports a form of progressive interlacing (a generalization of the Adam7 algorithm), which means that any partial download of a compressed file can be used as a reasonable lossy encoding of the entire image.

History

The format was initially announced publicly in September 2015,^[4] with the first alpha release occurring about a month later, in October 2015.^[1]

The first stable version of FLIF was released in September 2016.^[5]

Design

For compression, FLIF uses MANIAC (Meta-Adaptive Near-zero Integer Arithmetic Coding), a variant of CABAC where the contexts are nodes of decision trees which are dynamically learned at encode time.

FLIF uses the reversible YCoCg color space (unlike Y′C_BC_R that loses a bit of color information, independently of its use in otherwise lossy JPEG). Not yet implemented are some features,^[6] e.g. other "color spaces (CMYK, YCbCr, ...)". The color space conversion is faster, but the overall decoding (and encoding) is still slower than it needs to be, or some of the competition, even with the better color space as that is only a small fraction of the overall process. The format supports an optional alpha channel (RGBA) like PNG (but unlike JPEG); and progressive coding, similar to PNG (unlike it, progressive compression doesn't increase file-size), but as FLIF's algorithm is more complex (and partly, may not have had as much tuning of the implementation yet), it has a higher computational cost; at least lower bandwidth requirements can offset some of that extra time. Without the progressive coding, FLIF is faster, than otherwise.

FLIF has 1 to 16 bits per channel.

FLIF has some parameters, and can result in differently sized images, with tuning, or done by flifcrush tool. All of those images are still lossless. FLYF (for lossY), is also considered, and that would be the file-ending; while both could describe either and ending just used to indicate.

References

External links

• Official website
• FLIF on GitHub
• PolyFLIF - A Javascript library to decode FLIF in browsers
• Free Lossless Image Format at Open Hub
• Phew - native macOS FLIF viewer