A FLIF file is an image saved in the Free Lossless Image Format (FLIF). It contains an image or animation and uses lossless compression. FLIF files are used to store a variety of images such as photographs, geographical maps, and medical images.

FLIF is an alternative to PNG, WebP, JPEG2000, JPEG-LS, lossless JPEG XR, MNG, APNG, GIF, and lossless BPG formats and boasts a better compression ratio. The format supports RGB, RGBA, and grayscale with a color depth of 1 to 16 bits per channel. The FLIF format is made up of 4 parts: Main header - Contains metadata about the image, such as the height, width, depth, and number of frames. Optional metadata chunks - Contains non-pixel data, which includes an ICC color profile, encoded with DEFLATE compression. Second header - Contains information detailing how the pixel data is encoded. Pixel data - Contains pixel information encoded with MANIAC entropy coding. More information about the format can be found here. NOTE: The FLIF format was originally released in October of 2015 as an alpha release. The first stable version was released in September 2016.