What is HEIC, and should you keep it or JPEG?
My phone saves .heic files and nothing on my laptop will open them. What are they, and do I need them?
What HEIC stands for
HEIC commonly means High Efficiency Image Container. The .heic extension identifies a HEIF-family image file, usually containing pixels encoded with HEVC. In everyday use, people say HEIC when they mean the iPhone photo file, even though HEIF is the container standard and HEVC is usually the compression codec inside it.
That distinction explains why changing .heic to .jpg does not convert the photo. The file extension is only a label; software still finds HEIF structure and HEVC-compressed image data inside. A real conversion must decode those pixels and encode a new JPEG, PNG or WebP file.
HEIC is a container, not a codec
A .heic file is a HEIF file: the High Efficiency Image File Format, standardised as ISO/IEC 23008-12. HEIF is a container built on the same ISO base media file structure that MP4 uses. It says how images, thumbnails, depth maps, image sequences and metadata are arranged inside a file — it does not say how the pixels are coded.
In the files an iPhone produces, the pixels are coded with HEVC, also known as H.265, the video codec standardised as ITU-T H.265. That is the source of both the format's advantages and its problems: you are, in effect, storing a photograph as a single frame of a modern video codec.
Why the phone chose it
HEVC has intra-frame prediction tools that JPEG's 1992 design does not, so for the same visual quality it generally needs fewer bits. Storage on a phone is finite and photo libraries are not, so the saving is worth real money to a device maker. The container also lets one file hold several related images — the frames of a burst, the still and the short clip of a Live Photo, an alpha or depth channel — instead of scattering them across a folder.
There is a second benefit that matters more than size for some people: HEIF supports more than 8 bits per channel. A 10-bit image has far more room in gradients, which is why skies and skin tones survive editing better than they would in an 8-bit JPEG.
Why your other software refuses to open it
HEVC is a patented codec with licensing obligations for decoders. That is a legal and commercial fact, not a technical one, and it is the main reason support is uneven: some operating systems ship a decoder, some ship one only when a hardware decoder is present, and some browsers decode HEIC while others do not. A file that opens instantly on the phone that took it can be unreadable on a machine three metres away.
This is why FileSlimmer decodes HEIC but never writes it. Conversion runs in your browser, using the platform decoder when it exists and a self-hosted WebAssembly decoder when it does not, and the output is JPEG, PNG or WebP — formats the receiving software will actually open.
HEIC against JPEG, honestly
| Property | HEIC, meaning HEIF with HEVC | JPEG |
|---|---|---|
| Size at similar quality | Usually smaller | Usually larger |
| Bit depth | 8 or 10 bits per channel | 8 bits per channel |
| Transparency | Supported | Not supported |
| Multiple images in one file | Supported | Not supported |
| Opens on unfamiliar software | Often not | Almost always |
| Licensing | Patented codec | Effectively unencumbered |
What a HEIC file may be hiding
Because the container can hold a collection, a single .heic can contain more than the picture you see. A Live Photo carries a short image sequence alongside the still. A portrait shot may carry a depth map. A burst may carry many frames with one marked as primary. Converting to JPEG produces one flat image, so anything the container was carrying alongside the primary image is not present in the output.
Orientation is worth a separate mention. HEIC records rotation as metadata, exactly as JPEG does. A converter that ignores it produces sideways photographs. FileSlimmer applies the recorded orientation to the pixels during conversion, so the JPEG looks the way the phone displayed it.
So which copy do you keep?
- Keep the HEIC as your original if you stay inside an ecosystem that reads it and you value the smaller library and the extra bit depth.
- Convert to JPEG for anything you send outward: an upload form, a print service, an email attachment, a colleague on unknown software.
- Convert to PNG only when you need lossless output for editing; the file will be considerably larger than either of the other two.
- Do not convert HEIC to JPEG and then delete the HEIC, if the HEIC was your only original. The conversion is a lossy re-encode of an already lossy image.
Limitations worth knowing before you convert
Converting is a second lossy pass, so a small amount of quality is lost even at a high setting. If a browser cannot decode HEVC at all, and the self-hosted fallback decoder cannot handle a particular variant — an unusual profile, a damaged file, a codec other than HEVC inside the same container — the conversion fails rather than producing something wrong. FileSlimmer reports which file failed and why, and leaves the original untouched.
If you want to stop dealing with this at the source, most phone cameras have a compatibility setting that switches capture back to JPEG. You trade storage for the ability to hand a file to anyone.
Tools for this
Sources
- ISO/IEC 23008-12 — High Efficiency Image File Format
- ITU-T H.265 — High Efficiency Video Coding
- Nokia Technologies — HEIF technical overview