High Efficiency Image File Format (HEIF) specifies the storage of individual images as well as image sequences in a single container file. It is an MPEG standard and defined by part 12 of MPEG-H (ISO/IEC 23008-12).
| High Efficiency Image File Format (HEIF) | |
|---|---|
| Filename extension |
.heif, .heic |
| Internet media type |
image/heif, image/heic, image/heif-sequence, image/heic-sequence |
| Developed by | Moving Picture Experts Group (MPEG) |
| Type of format | Image Container Format |
| Standard | ISO/IEC CD 23008-12 |
| Website | http://mpeg.chiariglione.org/standards/mpeg-h/image-file-format |
HEIF specification defines the means of storing High Efficiency Video Codec (HEVC) encoded intra images and HEVC encoded image sequences in which inter prediction is applied in a constrained manner.
HEIF files are compatible with the ISO Base Media File Format (ISOBMFF, ISO/IEC 14496-12) and can also include other media streams, such as timed text and audio.
History
The requirements and main use cases of HEIF were defined in 2013 [1][2].The technical development of the specification took about 1.5 years and was finalized in summer 2015[3].
Use Cases
Some main use cases supported by HEIF are as follows[1][2]:
- Storage of single or multiple images and their thumbnails,
- Storage of burst photos,
- Support for simultaneous capture of video and still images, i.e. storing still images and timed image sequences into the same file,
- Efficient representation of animations and cinemagraphs,
- Storage of focal and exposure stacks into the same container file,
- Storage of images derived from other images of the file, either as derived images represented by non-destructive image editing operations or as pre-computed derived images,
- Support for storing other media, such as audio and timed text, into the same container file with timed image sequences and synchronizing their playback.
As HEVC provides support for various chroma formats and sample fidelities up to lossless coding, the format can serve the whole spectrum of use cases from today's consumer devices storing images typically at 8 bits per sample to high-end professional devices with sample fidelity and dynamic range requirements going all the way up to 16 bits per sample. Some usage scenarios that are facilitated by HEIF are described below:
Digital cameras and smartphones:
In order to save storage space [TODO: x-ref to compression results], HEIF-encapsulated HEVC-coded images can be used for compressing the full-resolution images while keeping a lower-resolution JPEG copy (e.g. at 4K resolution or below) for on-screen displaying purposes.
Digital cameras and smartphones can use HEIF to achieve convenient one-file packaging of burst photos, focal stacks, and exposure stacks. Similarly, simultaneously captured video and still images can be stored in the same HEIF file. HEIF also enables storage of any image collections into a single file, hence they can be shared easily.
Web pages and Internet-connected image applications:
The picture element of HTML5.1 provides the capability of indicating multiple alternatives for the same image, out of which the web browser can select the one that best suits its purpose. A motivation for web pages and connected applications to start using HEIF is to reduce the web page and/or image content download times [TODO: x-ref to compression results].
Image editing:
Changing of the orientation and cropping are basic features of HEIF and require no re-encoding of the images. Additionally, HEIF introduces a framework for non-destructive editing operations, which can be specified by external specifications. This feature can be used by image editing applications so that the editing instructions are kept in the same file as the original image.
Features
In ISOBMFF, a continuous or timed media/metadata stream forms a track, whereas static media or metadata are stored as items. Consequently, HEIF has the following basic design:
- Still images are stored as items. All image items are independently encoded and do not depend on any other item in their decoding. Any number of image items can be included in the same file.
- Image sequences are stored as tracks. An image sequence track can be indicated to be displayed either as a timed sequence or in a non-timed manner, such as a gallery or album of images. When there is coding dependency between images, an image sequence track is used instead of image items.
- A file may contain both image items and image sequence tracks along with other media. For example, it is possible to create a HEIF file, which includes image items or image sequence tracks conforming to HEIF, and audio and/or timed text tracks conforming to any derivative format of the ISOBMFF
Keeping the above-mentioned design principles in mind, HEIF files can store the following types of data[4]:
- Image Items: storage of individual images, image properties and thumbnail(s).
- Image Derivations: derived images are generated during run-time based on descriptions such as rotation, grid and overlay. These images depend on other images stored in the HEIF file. 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 even when tens of images are stored in the same HEIF file.
- Auxiliary Image Items: storage of an image data which complements another image item. An alpha plane or a depth map are examples for such images. This data is 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.
Examples of above-mentioned entities can be found here.
Comparison
Below table shows a comparison of different image formats[4]:
| HEIF (.heic) | JPEG/Exif | PNG | GIF (89a) | WebP | JPEG-XR / TIFF | JPEG-XR / JPX | BPG | |
|---|---|---|---|---|---|---|---|---|
| Formats and extensibility | ||||||||
| Base container file format | ISOBMFF | TIFF | - | - | RIFF | TIFF | - 4 | - |
| Lossy compression | Yes (HEVC) | Yes (JPEG) | No | No | Yes (VP8) | Yes | Yes | Yes (HEVC10) |
| Lossless compression | Yes (HEVC) | Yes (TIFF Rev 6.0) | Yes (PNG)1 | Yes (GIF)1 | Yes (VP8L) | Yes | Yes | Yes (HEVC10) |
| Extensible to other coding formats | Yes | Yes8 | No | No | No | Yes8 | Yes5 | No |
| Metadata format (on top of internal) | Exif, XMP, MPEG-7 | Exif | - | - | Exif, XMP | Exif, XMP | JPX, (XMP)6 | Exif, XMP |
| Extensible to other metadata formats | Yes | No | No | No | No | No | Yes (XML-based) | Yes |
| Other media types (audio, text, etc.) | Yes | Audio2 | No | No | No | No | Yes7 | No |
| Multi-picture features | ||||||||
| Multiple images in the same file | Yes | No11 | No | Yes3 | Yes3 | No | Yes | Yes9 |
| Image sequences / animations | Yes | No | No | Yes | Yes | No | Yes | Yes |
| Image coding | Yes | No | No | No | No | No | No | Yes |
| Derived images | ||||||||
| Multiple-of-90-degree rotations | Yes | Yes | No | No | No | Yes | Yes | No |
| Cropping | Yes | No | No | No | No | No | Yes | No |
| Tiling/overlaying | Yes | No | No | No | Yes | No | Yes | No |
| Extensible to other editing operations | Yes | No | No | No | No | No | No | No |
| Auxiliary picture information | ||||||||
| Transparency (alpha plane) | Yes | No | Yes | No12 | Yes | Yes | Yes | Yes |
| Thumbnail image | Yes | Yes | No | No | No | Yes | Yes | Yes |
1 In GIF and indexed color PNG encoding, lossy color quantization is applied while the color-quantized image is losslessly compressed.
2 PCM, µ-Law PCM and ADPCM encapsulated in RIFF WAV
3 Only for animations and tiling/overlaying
4 JPX is a box-structured format compatible with ISOBMFF. However, only the File Type box is common in JPX and ISOBMFF.
5 Encapsulation of JPEG-2000 and JPEG-XR have been specified for JPX container. Mappings for other codecs could be similarly specified.
6 JPX (ITU-T T.800 and T.801) specifies an own metadata schema, but is capable of carrying an XML formatted metadata, such as XMP.
7 JPX can contain media complying with ISOBMFF (or derivatives thereof). No accurate synchronization between JPX animations and other media.
8 TIFF as a container format facilitates extensions to other coding formats.
9 Only for animations, thumbnails, and alpha planes. Non-timed image collections not supported.
10 HEVC Main 4:4:4 16 Still Picture profile, Level 8.5, with additional constraints
11 Can be enabled through the MP extension
12 A palette index for fully transparency can be specified.
The following references are used in the comparison:
| Image format | Version or date | Reference and/or URL |
|---|---|---|
| HEIF (.heic) | 03/2015 | ISO/IEC 23008-12 |
| JPEG | ISO/IEC 10918-1 | ITU-T Rec. T.81 | |
| Exif | http://www.cipa.jp/std/documents/e/DC-008-2012_E.pdf | |
| PNG | http://www.w3.org/TR/PNG/ | |
| GIF | 89a | http://www.w3.org/Graphics/GIF/spec-gif89a.txt |
| WebP | https://developers.google.com/speed/webp/docs/riff_containerVP8L: https://developers.google.com/speed/webp/docs/webp_lossless_bitstream_specification | |
| JPEG-XR | ISO/IEC 29199-2 | ITU-T Rec. T.832
ISO/IEC 15444-2 | ITU-T Rec. T.801 (for JPX) | |
| BPG | 0.9.5 | http://bellard.org/bpg/bpg_spec.txt |
Note: It is acknowledged that a summary such as that in the comparison table might be somewhat incomplete when it comes to features of different formats. For example, the table does not cover some of the extensions of JPEG.
TODO: Add compression performance.
References
- ^ a b "Requirements for still image coding using HEVC | MPEG". mpeg.chiariglione.org. Retrieved 2015-11-25.
- ^ a b "Requirements for HEVC image sequences | MPEG". mpeg.chiariglione.org. Retrieved 2015-11-25.
- ^ "Evidence motivates MPEG to launch new standardization effort for HDR".
- ^ a b M. M. Hannuksela, E. B. Aksu, V. K. Malamal Vadakital, J. Lainema. "Overview of the High Efficiency Image File Format". JCT-VC document JCTVC-V0072, Oct. 2015.
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