Apple’s HEIF and HEVC

At this year’s WWDC, Apple introduced a new format for still images and video. The container is called High Efficiency Image Format (HEIF), and it uses a codec called High Efficiency Video Coding (HEVC). HEIF files can store still images, video, or both at once. Apple doesn’t have proper documentation on its site, as far as I can see, but a slideshow on HEIF and one on HEVC provide a lot of information. Kelly Thompson provides a technical overview.

Apple boasts that HEIF is more efficient than JPEG. That’s not a high bar. Many formats exist that improve on JPEG in various ways, but none have displaced it. Familiarity and broad support still beat quality and cutting-edge status. It’s questionable whether Microsoft will jump to adopt a standard that Apple has tied so closely to its own brand. Adobe needs to bless it in Photoshop before it can claim to have arrived.

What exactly is this format? HEIF is based on MPEG-H, aka ISO/IEC FDIS 23008-12, Carriage of Still Image and Image Sequences. This is a standard which is still under development. The most useful source of technical details seems to be this GitHub site.

A single container can store multiple images, video, animations, timed text, and audio. Alternative representations of images can exist in a container, so one file could contain images optimized for desktop and mobile viewing, as well as a thumbnail. The format offers both lossy and lossless compression. An image can include a transparency (alpha) plane. Metadata options include Exif, XMP, and MPEG-7. An image can include a depth map, specifying how far parts of the image are from the point of view.

HEIF is the default internal format on the latest iOS. MacOS High Sierra also supports the format. Exported files from iOS devices will be converted to JPEG, so the main advantage currently is that you can store more pictures. Apple surely plans to change this as HEIF becomes available on other operating systems.

Licensing and patents will be an issue, but it looks as if software developers can implement HEIC without paying royalties. Hardware support is a different matter.

JPEG is now only the second most popular image format on the Web, but it’s still the most popular one supporting lossy compression (PNG outranks it in websites using the format). It’s overdue for replacement by something better. Will that be HEIF? I won’t try to guess.

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