High Efficiency Image File Format (HEIF) is a digital container format for storing individual digital images and image sequences. The standard covers multimedia files that can also include other media streams, such as timed text, audio and video. HEIF can store images encoded with multiple coding formats, for example both SDR and HDR images. HEVC is an image and video encoding format and the default image codec used with HEIF. HEIF files containing HEVC-encoded images are also known as HEIC files and are mandated to use the .heic filename extension or .heics as stated in the standard. Such files require less storage space than the equivalent-quality JPEG files of the same images. HEIF files are a special case of the ISO base media file format (ISOBMFF, ISO/IEC 14496-12), first defined in 2001 as a shared part of MP4 and JPEG 2000. Introduced in 2015, it was developed by the Moving Picture Experts Group (MPEG) and is defined as Part 12 within the MPEG-H media suite (ISO/IEC 23008-12).
History The requirements and main use cases of HEIF were defined in 2013. The technical development of the specification took about one and a half years and was finalized in the middle of 2015. Apple was the first major adopter of the format in 2017 with the introduction of iOS 11 using the HEIC variant. While HEIC became the default for iPhones, it is possible to revert the settings to allow photos to be recorded in the JPEG format. Android devices containing the appropriate hardware encoders received support for HEIC files with the release of Android 10 (2019). On some systems, pictures stored in the HEIC format are converted automatically to the older JPEG format when they are sent outside of the system, although incompatibility has led to problems such as US Advanced Placement test takers failing due to their phones uploading unsupported HEIC images by default, leading the College Board to request students change the settings to send only JPEG files. Although HEIC is gaining in popularity, it is not universally supported; Adobe Photoshop is an example of common image-editing software that only supports HEIC with color depth of 8-bit, and not 10- or 12-bit. As of 2022 camera hardware (including on mobile devices) is increasingly supporting HEIC file output, with color depth often higher than 8-bit color.
Specifications HEIF files can store the following types of data:
Image items Storage of individual images, image properties and thumbnails. HEIF can store a picture as a set of independent rectangular tiles. Equal-sized tiles are combined with a derived grid item; tiles of mixed size use overlay/location properties instead. A decoder can then decode only the tiles needed for a visible region, which Apple described as useful for pan and zoom without loading the full image into memory.HEIF does not require a particular tile size. Apple's HEIC stills are encoded as a grid of 512px by 512px tiles; Android typically use the same tile size; cameras tend to use much larger tiles. Image derivations Derived images enable non-destructive image editing, and are created on the fly by the rendering software using editing instructions stored separately in the HEIF file. These instructions (rectangular cropping, rotation by one, two or three quarter-turns, timed graphic overlays, etc.) and images are stored separately in the HEIF file, and describe specific transformations to be applied to the input images. The storage overhead of derived images is small. Image sequences Storage of multiple time-related and/or temporally predicted images (like a burst-photo shot or cinemagraph animation), their properties and thumbnails. Different prediction options can be used in order to exploit the temporal and spatial similarities between the images. Hence, file sizes can be drastically reduced when many images are stored in the same HEIF file. Auxiliary image items Storage of image data, such as an alpha plane or a depth map, which complements another image item. These data are not displayed as such, but used in various forms to complement another image item. Image metadata Storage of Exif, XMP and similar metadata which accompany the images stored in the HEIF file.
Encodings inside the container The HEIF container can store files encoded with various codecs, including:
HEVC AV1 AVC VVC EVC JFIF (JPEG) JPEG 2000 As users cannot easily tell what encoding and encoding parameters an image was stored in, the HEIF container format can be confusing and makes comparison statements like “HEIF is better than JPEG” vague and inaccurate. Simply knowing a file is in the HEIF container does not reveal much information, as it could be:
a JFIF (JPEG), a poor quality (default settings) AV1, a very high quality AV1 encoding (which takes a lot of processing to encode), an HEVC with poor quality parameters, or an HEVC with high quality parameters.
MIAF The Multi-Image Application Format (MIAF) is a restricted subset of HEIF specified as part of MPEG-A. It defines a set of additional constraints to simplify format options, specific alpha plane formats, profiles and levels as well as metadata formats and brands, and rules for how to extend the format.
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