Remove Metadata From HEIC Photos

How a HEIC file stores metadata

HEIC is an image format built on the ISO base media file format — the same box structure as an MP4 video. Instead of one stream of image data, the file holds a list of items: on an iPhone, a full-size photo is split into a grid of HEVC-compressed tiles, and the grid, the thumbnail, the depth map and the HDR gain map are each items of their own.

Metadata is stored the same way. EXIF is an item of type 'Exif', and XMP is an item of type 'mime' with an XML content type. A reference table links each of them to the image it describes.

• Exif item — camera make and model, lens, exposure, the date and time taken, and GPS coordinates, plus Apple's MakerNote with capture settings and the identifier that pairs a Live Photo with its video.
• mime item (XMP) — editing history and creator fields. Recent iPhones attach a second XMP packet to the HDR gain map.
• uuid box — where C2PA content credentials are stored in this container family.
• iloc — the item location table: where in the file each item's bytes begin and how long they are.
• iprp — item properties: the stored size (ispe), the rotation (irot) and the colour profile (colr).

Why the photo is not converted to JPEG

The usual advice for cleaning an iPhone photo is to convert it to JPEG first. That works, but it decodes every pixel and compresses the picture again with an older codec. Quality is lost, and because HEVC compresses better than JPEG, the copy is usually larger than the photo it came from.

Here the HEIC is rewritten instead. The EXIF and XMP items are dropped from the item tables, their bytes are cut out of the file, and every tile, the thumbnail and the gain map are copied across byte for byte. The cleaned file is still a HEIC, at the original quality.

The part that makes HEIC harder than JPEG

In a JPEG, metadata sits in its own segments at the front, so leaving a segment out moves nothing else. HEIC records the position of every item as a byte offset in the item location table. Remove a few hundred bytes of EXIF and every item stored after it is now in the wrong place.

So after the cut, each surviving offset is recalculated — for data in the main media box and for the small data box inside the metadata, where iPhones keep the grid description. The cleaned file is then read back from scratch, and the tool reports what it finds there rather than what it intended to remove.

What is kept, and why

Rotation survives without any special handling. A HEIC stores it as the irot property of the image, not as an EXIF tag, so a photo shot in portrait is still displayed upright after its EXIF is gone.

The thumbnail, depth map and HDR gain map are images, not metadata, and are kept unchanged. The colour profile is kept by default, because removing it can shift colours in Display P3 photos; there is a toggle to remove it too.