JPG vs HEIC

HEIC holds a still frame coded with HEVC, the video codec that succeeded H.264, and applying video compression to a photograph works about as well as it sounds. A picture that is four megabytes as a JPEG is commonly two as a HEIC, at quality most people cannot tell apart.

That is why Apple switched the default in 2017. On a phone holding several thousand photographs it is genuinely a doubling of capacity, and it happens without anybody choosing anything. It is a real technical advance, and it is also the reason a great many people now have a folder of files that nothing on their computer will open.

Wide colour and high dynamic range, which is what makes a photograph look right on a modern display and washed out after a careless conversion. The extra range is not extra bit depth: an iPhone capture is eight bits per channel, the same as a JPEG, and the highlights ride in a separate gain map stored beside the picture. Ten-bit belongs to ProRAW and ProRes, not to the photographs in your camera roll.

And it is a container rather than a single image, which is how Live Photos work: the still, the short video, and the depth map from portrait mode all live in one file. Convert that to JPEG and you get the still. Everything else is silently discarded, which is worth knowing before converting a library rather than after.

Patents. HEVC is covered by several patent pools with terms that a good deal of the industry declined to accept, so support was not simply a matter of implementing a format. Windows still asks for a paid codec from the Store. Many browsers do not display HEIC. Older editing software, plenty of upload forms, print services and countless web applications reject it outright.

This is not a technical shortcoming of the format and it does not matter to the person holding the file — the practical effect is identical either way. A photograph in a format the destination refuses is a photograph you cannot use.

On an iPhone: Settings, Camera, Formats, and choose "Most Compatible" instead of "High Efficiency". The camera then records JPEG and the problem never occurs again, at the cost of roughly double the storage per photograph.

There is also a partial safety net already in place. Transfers to Windows and many shares convert to JPEG automatically, which is why some photographs arrive usable and others do not — AirDrop to a Mac, direct card copies and some cloud syncs keep the original. If some of your photographs open and some do not, that inconsistency is the explanation.

The conversion itself is routine, and two things are worth getting right. Colour: HEIC carries wide-gamut data and a conversion that ignores the colour profile produces JPEGs that look flat and desaturated compared with the phone. Any decent converter handles it; a careless one does not, and it is very visible on skies and skin.

And metadata. Dates, camera settings and location are in the file, and a conversion that drops them leaves a photo library that will not sort chronologically — which is a great deal of work to undo across a few thousand images. Convert five, look at them properly, then convert the rest.

Converting is a lossy re-encode: the HEIC was already compressed, and the JPEG compresses the decoded result again. Once for practical use is fine. Doing it because the folder should be tidy, and deleting the originals, is throwing away the better copy.

Keep the HEIC as the master where you can, and generate JPEGs for whatever needs them — an upload, a print order, a document, a colleague. The originals also hold the gain map and the Live Photo, and no conversion recovers either.

AVIF is technically the same idea done royalty-free: a still frame of a modern video codec, similar sizes, similar wide-colour support, and no patent pool. Every current browser displays it, which HEIC cannot claim.

What it does not have is a phone camera writing it by default, so it is not what your photographs are. For the web, AVIF is the format to serve. For the pictures on your iPhone, the choice remains HEIC for storage and JPEG for everything that has to leave the device.