What is a HEIC file?

A HEIC file is a photograph in the format iPhones have used by default since 2017. It holds roughly the same picture as a JPEG in about half the space, and a great deal of software outside Apple’s world still refuses to open one.

That refusal is the reason most people go looking for an explanation, and the honest one is more interesting than "it is Apple’s format": the incompatibility is a licensing decision, not a technical limitation, and the two names involved describe two different things.

HEIC and HEVC are not the same thing

This is where nearly every explanation goes vague, and the distinction is the key to everything else.

HEIF — High Efficiency Image File Format — is a container. It is a box that can hold one image, several images, a burst, an animation, a depth map, a thumbnail and a pile of metadata, and it says nothing at all about how the picture inside is compressed.

HEVC — High Efficiency Video Coding, also called H.265 — is the codec. It is the compression the picture actually uses, and it is a video codec: a HEIC photo is essentially a single frame of video, encoded with the same technology that compresses 4K streams.

HEIC is the file extension Apple uses for HEIF-containing-HEVC. So the extension names the box, the compression is a video codec, and that mismatch explains the peculiar situation where a machine can be missing one piece and not the other. It is also why Windows asks you to install two separate extensions.

Why Apple switched, and what it bought

iOS 11 made HEIC the camera default in 2017, at a moment when phones were shooting more and larger photos and storage was the thing people complained about. The saving is real: about half the bytes for a picture nobody could distinguish from the JPEG equivalent.

The container earned its place too, because a modern phone photo is not one image. A portrait-mode shot carries a depth map so the background blur can be adjusted afterwards. A Live Photo pairs the still with a short video. HDR shots carry 10 bits per colour channel where JPEG has 8, which is what stops a sunset from banding. A JPEG can hold exactly one image and none of that.

Why so little else opens it

Because HEVC is patent-encumbered. Licensing it costs money, paid to several patent pools at once, and that cost falls on whoever ships a decoder. Apple absorbed it. Others declined.

Windows offers a free HEIF extension, while the HEVC video extension it often needs alongside is a paid item in the Microsoft Store.
Chrome still will not decode a HEIC image, which is why web upload forms reject them so consistently.
Android has read HEIF for years, though support in individual apps remains uneven.
Older desktop editors frequently cannot open one at all.

None of this is a limitation of the format. It is the predictable result of a good codec with an expensive licence, and it is why AVIF — which is genuinely comparable and royalty-free — has had a much easier time being adopted on the web.

What conversion costs you

Converting to JPG loses a little detail in the re-encode, which you will not see, and three things you might:

The depth map. The picture keeps whatever blur was applied when it was saved, but the blur is no longer adjustable, because the information it was computed from is gone.
The Live Photo. The paired video has nowhere to live in a JPEG. It has to be saved as a video file from the phone; no image format will hold it.
10-bit colour. JPEG stores 8 bits per channel, so a wide-gamut HDR photograph is flattened. On most pictures this is invisible; on a gradient sky it is the difference between smooth and banded.

Everything else survives, and one thing you may not want to survive does not: because the picture is decoded and redrawn, the camera, timestamp and GPS coordinates are left behind. That is a side effect rather than a guarantee — what EXIF data is covers where it does and does not happen.

The setting worth changing, and the one that is not

In Settings → Camera → Formats, "High Efficiency" shoots HEIC and "Most Compatible" shoots JPEG. The second sounds like the fix and usually is not: it roughly doubles what every photo costs in storage, and it gives up the depth and colour information for photos you were never going to send anyway.

The better arrangement for most people is to leave High Efficiency on and let Settings → Photos → Transfer to Mac or PC → Automatic convert on the way out. The library stays small and anything leaving the phone arrives as a JPEG. Switch to Most Compatible only if you routinely AirDrop or attach photos straight from the camera roll to people on Windows.

What to do with the HEICs you already have

Keep them, and convert copies. The originals are smaller and better than the JPEGs you would replace them with, and Apple software opens them natively. When something else needs the photo, convert to JPG for anything going to a form, an email or a person, or to PNG if it is going to be edited repeatedly. If a document is what somebody has asked for, HEIC to PDF skips a step.

Questions

Should I turn HEIC off on my iPhone?

Only if you send photos straight off the phone more often than you store them. Switching Camera settings to "Most Compatible" makes every new photo a JPEG, which roughly doubles the storage each one takes and loses the depth and 10-bit information. "High Efficiency" with conversion on sharing is the better setting for most people: the library stays small, and anything you AirDrop or attach is converted on the way out.

Why will Windows not open my HEIC files?

Because the codec inside is patent-encumbered and Microsoft would have to pay to include it. Windows offers the HEIF extension free but the paired HEVC video extension is a paid item in the Store, and which of them a given machine needs varies confusingly. It is a licensing situation rather than a technical limitation, which is why it has persisted for years rather than being quietly fixed.

Is HEIC better quality than JPEG?

At the same file size, clearly yes. HEIC uses a modern video codec, supports 10 bits per colour channel against JPEG’s 8, and holds up far better in skies and shadows where JPEG shows banding. At maximum quality both are good enough that the difference is academic. The real advantage is that a HEIC of equal visible quality is about half the size.

Does converting HEIC to JPG lose anything?

Some detail, invisibly, plus three things that have nowhere to go: the depth map used for portrait blur, the paired video of a Live Photo, and the extra colour precision of 10-bit capture. If the photo is a portrait-mode shot you want to keep editable, export it from Photos with the effect applied rather than converting the raw HEIC.