Free Lossless Image Format (FLIF) is a

lossless Lossless compression is a class of data compression that allows the original data to be perfectly reconstructed from the compressed data with no loss of information. Lossless compression is possible because most real-world data exhibits statisti ...

image format claiming to outperform PNG, lossless

WebP WebP is a raster graphics file format developed by Google intended as a replacement for JPEG, PNG, and GIF file formats. It supports both lossy and lossless compression, as well as animation and alpha transparency. Google announced the WebP ...

, lossless BPG and lossless

JPEG 2000 JPEG 2000 (JP2) is an image compression standard and coding system. It was developed from 1997 to 2000 by a Joint Photographic Experts Group committee chaired by Touradj Ebrahimi (later the JPEG president), with the intention of superseding their ...

in terms of compression ratio on a variety of inputs. FLIF supports a form of progressive interlacing (a generalization of the

Adam7 algorithm Adam7 is an interlacing algorithm for raster images, best known as the interlacing scheme optionally used in PNG images. An Adam7 interlaced image is broken into seven subimages, which are defined by replicating this 8×8 pattern across the f ...

) with which any partial download (greater than couple hundred bytes) of an image file can be used as a lossy encoding of the entire image. Jon Sneyers, one of the developers of FLIF, since combined it with ideas from various lossy compression formats to create a successor called the Free Universal Image Format (FUIF), which itself was combined with

Google Google LLC (, ) is an American multinational corporation and technology company focusing on online advertising, search engine technology, cloud computing, computer software, quantum computing, e-commerce, consumer electronics, and artificial ...

's PIK format to create

JPEG XL The JPEG XL Image Coding System is a royalty-free open standard for a image compression, compressed Raster graphics, raster image format. It defines a graphics file format and the abstract device for coding JPEG XL bitstreams. It is developed by t ...

. As a consequence, FLIF is no longer being developed.

History

The format was initially announced publicly in September 2015, with the first

alpha release The software release life cycle is the process of developing, testing, and distributing a software product (e.g., an operating system). It typically consists of several stages, such as pre-alpha, alpha, beta, and release candidate, before the fi ...

occurring about a month later, in October 2015. The first stable version of FLIF was released in September 2016.

Design

For compression, FLIF uses MANIAC (Meta-Adaptive Near-zero Integer

Arithmetic Coding Arithmetic coding (AC) is a form of entropy encoding used in lossless data compression. Normally, a String (computer science), string of characters is represented using a fixed number of bits per character, as in the American Standard Code for In ...

), 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 A color space is a specific organization of colors. In combination with color profiling supported by various physical devices, it supports reproducible representations of colorwhether such representation entails an analog or a digital represe ...

(unlike that loses some color information to rounding errors, independently of its use in otherwise lossy

JPEG JPEG ( , short for Joint Photographic Experts Group and sometimes retroactively referred to as JPEG 1) is a commonly used method of lossy compression for digital images, particularly for those images produced by digital photography. The degr ...

). Not yet implemented are some features, e.g. other "color spaces (

CMYK The CMYK color model (also known as process color, or four color) is a subtractive color model, based on the CMY color model, used in color printing, and is also used to describe the printing process itself. The abbreviation ''CMYK'' refers ...

, 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 In computer graphics, alpha compositing or alpha blending is the process of combining one image with a background to create the appearance of partial or full transparency. It is often useful to render picture elements (pixels) in separate pass ...

( RGBA) like PNG (but unlike

); 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. Progressive coding reduces FLIF's performance. FLIF supports

grayscale In digital photography, computer-generated imagery, and colorimetry, a greyscale (more common in Commonwealth English) or grayscale (more common in American English) image is one in which the value of each pixel is a single sample (signal), s ...

, RGB and RGBA with

color depth Color depth, also known as bit depth, is either the number of bits used to indicate the color of a single pixel, or the number of bits used for each color component of a single pixel. When referring to a pixel, the concept can be defined as bit ...

of 1 to 16 bits per channel. FLIF has some tuning parameters which can result in differently sized images. All of the images are still lossless. A flifcrush tool is also available to achieve the minimal size. Lossy compression can be achieved by preprocessing. The process is deterministic and does not cause

generation loss Generation loss is the loss of quality between subsequent copies or transcodes of data. Anything that reduces the quality of the representation when copying, and would cause further reduction in quality on making a copy of the copy, can be con ...

Support

] *

XnView XnView is an image organizer and general-purpose file manager used for viewing, converting, organizing and editing raster images, as well as general purpose file management. It comes with built-in hex inspection, batch renaming, image scan ...

supports FLIF since version 2.36. * ExifTool supports reading and writing metadata in FLIF images since version 10.31.
UGUI-FLIF
supports preview and converting PNG file to FLIF. * IrfanView supports reading FLIF images since version 4.52.

References

External links

* – official site *
PolyFLIF
– a Javascript library to decode FLIF in browsers *
Phew
– native

macOS macOS, previously OS X and originally Mac OS X, is a Unix, Unix-based operating system developed and marketed by Apple Inc., Apple since 2001. It is the current operating system for Apple's Mac (computer), Mac computers. With ...

FLIF viewer
FLIF Optimizer
– tuning parameters for better lossless compression {{Compression formats Animated graphics file formats Graphics file formats Graphics standards Open formats Image compression