HEIC, HDR gain maps and Live Photos: why converting iPhone photos loses them

An iPhone photo is often more than one image. Here is what a HEIC file holds, what a quick JPEG conversion throws away, and how to keep it.

Updated Oct 18, 20266 min read

You copy a photo from your iPhone, convert it to JPEG, and something is off. The bright sky that glowed on your phone looks flat. The Portrait blur can no longer be adjusted. The Live Photo no longer moves.

Nothing is broken. A modern iPhone photo is often several pieces of data packed together, and a quick conversion keeps only the main picture. This guide explains what those pieces are, what conversion drops, and how to keep them.

The short answer: keep the original HEIC as your master file, turn on Keep Originals so your iPhone stops converting photos when you copy them to a computer, and only convert a copy, with an app that says it supports HDR gain maps. A Live Photo's motion lives in a separate video, so no JPEG can keep it. The rest of this page explains why.

What a HEIC file holds

HEIC is Apple's name for photos stored in the HEIF format with HEVC compression. Apple uses it because it compresses better than JPEG, so photos take less space [1].

HEIF is a container. Besides the main image, it can hold extra images and data that belong to the same photo:

The main image.
An HDR gain map, which tells HDR screens how much brighter each area should be.
Depth data for Portrait photos. Apple's frameworks read depth from HEIF, JPEG and DNG files as auxiliary data stored alongside the image [9].
Metadata: EXIF, GPS, Apple's MakerNotes and a colour profile.

A JPEG can carry some of this too, but in a different way. Depth, for example, is stored as metadata inside a HEIC but as a second image inside a JPEG [10]. A converter has to know both layouts to move the data across.

HDR gain maps, in plain terms

An HDR screen can show highlights much brighter than a normal screen. A gain map is how one file serves both.

The file stores a normal (SDR) picture that looks right everywhere, plus a smaller map that says how much to brighten each pixel to get the HDR version [2]. An app that understands the map shows the brighter version on an HDR display. An app that does not shows the normal picture, so nothing breaks [2].

For years, Apple and Google wrote gain maps differently. That is settling down:

ISO 21496-1, the international standard for gain map metadata, was published in July 2025 [3]. Apple introduced its support as Adaptive HDR at WWDC24 [4].
Android's Ultra HDR JPEG stores the gain map as a second JPEG inside the file, using the Multi-Picture Format (MPF) [2].
Android 15 can write both Ultra HDR and ISO 21496-1 metadata in the same JPEG, using one gain map image [2].

Live Photos are two files

A Live Photo records 1.5 seconds before and after you press the shutter [7]. It is stored as a still image plus a short video. The two are paired by a shared identifier: the still carries it in Apple's MakerNotes and the video carries the same value in its QuickTime metadata [8].

Two things follow. A single JPEG can only hold the still, so the motion is gone after conversion. And if the identifier is lost from either file, the two stop pairing.

What a JPEG conversion drops

What you lose depends on the converter. This table shows what to check.

Part of the photo	In the original HEIC	After a basic JPEG conversion
Main picture	HEVC-compressed	Re-encoded as JPEG
HDR gain map	Stored with the image	Often dropped; some tools rewrite it in another gain map format [5]
Depth (Portrait)	Auxiliary data in the container [9]	Dropped unless the tool writes it as a second JPEG image [10]
Live Photo motion	A separate paired video [8]	Not part of a JPEG; only the still survives
EXIF, GPS, MakerNotes	In the file	Copied by many tools, but not all

Two real examples show how easy it is to lose the gain map:

A developer on Apple's forums reported that Apple's own Core Image could keep an ISO 21496-1 gain map when writing HEIC, but turned it into Apple's older gain map format when writing JPEG, or lost the HDR data, depending on the option [5].
The Ghost publishing platform strips gain maps from uploaded photos because Sharp, the image library it uses, did not support them. As of September 2025, libvips, the engine underneath Sharp, had added support, while Sharp and Ghost still had to follow [6].

If a website or app re-encodes your upload with a library like that, you get the flat version, even if you uploaded the right file.

How to keep them

Start with the setting that converts photos without asking.

On iPhone: Keep Originals. When you copy photos to a computer over USB, iOS may convert them to JPEG. To stop that, open Settings, then Photos (under Apps on recent iOS), and choose Keep Originals [1].

On iPhone: Most Compatible. Under Settings > Camera > Formats, Most Compatible makes the camera shoot JPEG instead of HEIF [1]. Only switch to it if you need JPEG for every photo.

Share Live Photos as Live Photos. When you share, the LIVE button controls whether the motion goes too. Sharing by Mail sends only the still [7].

Then, every time you convert or edit:

Keep the original HEIC as your master copy.
Convert a copy, never the only file.
Use an app that says it supports HDR gain maps (or Ultra HDR / ISO 21496-1) if you want HDR in the JPEG.
Open the result on an HDR screen and compare it with the original.
Check the file with a metadata viewer to see what came across.

Where FluidGhost fits

Our free photo check reads JPEG and HEIC files in your browser. For a HEIC, it reports whether the container still holds an Apple auxiliary image (depth or HDR gain map), whether the Exif item and Apple MakerNotes are there, and whether it found the HEVC image data. That makes it a quick way to see what a converter kept.

FluidGhost itself makes fresh copies of photos and videos for the accounts you manage. It is not an archival converter. When it writes a JPEG copy that has an HDR gain map, that map is generated from the new copy's own pixels rather than carried over from your original. If you care about your camera's exact HDR rendition, keep your original HEIC.

FAQ

Does converting HEIC to JPEG reduce quality?

It re-encodes the picture, and depending on the converter it can also drop the HDR gain map, depth data and Live Photo motion. Keep the original HEIC and convert a copy when you need JPEG.

Can a JPEG be HDR?

Yes. A JPEG can carry a gain map as a second image inside the file. Apps that understand it show the brighter HDR version; older apps show the normal image.

Why does my photo look flatter after I upload it?

The service may have re-encoded the image with a pipeline that drops the gain map, so you see only the standard version. Some widely used image libraries did not support gain maps until recently.

How do I stop my iPhone converting photos when I copy them to a computer?

Open Settings, then Photos (under Apps on recent iOS), and choose Keep Originals. The photos then copy as HEIC instead of being converted.

Is a Live Photo one file?

No. It is a still image and a short video that share a matching identifier. A single JPEG can only hold the still.