Convert HEIC to PNG

HEVC frame to PNG pixels

A HEIC holds a still frame compressed with HEVC, the codec of 4K video, which is why a phone can store a photo in 2 MB. Decoding that frame produces ordinary 8-bit pixels, and the PNG stores them exactly. Nothing in the picture changes; what changes is that the compression HEVC applied is now baked in rather than described, and every later save costs nothing.

A recent iPhone writes more into the file than the frame: an HDR gain map that lets Photos show highlights brighter than white, a depth map on Portrait shots, several frames in a burst. Only the main frame is read. The result is the standard-range rendering of the shot — the one you would see on any screen that is not an iPhone — with the gain map's extra highlights gone.

The orientation flag is applied before the pixels are written, so a photo taken in portrait comes out upright rather than sideways with a note saying to rotate it. The EXIF block itself is not copied into the PNG; PNG can carry it, but a re-encode here drops it, which for a photo going anywhere public is usually what you want.

When you want something else

For archiving rather than editing, keep the HEIC: it is smaller, holds the HDR and depth data, and every Apple device and modern Windows reads it. For editing in a serious tool, export a 16-bit TIFF from Photos or darktable instead — an 8-bit PNG has already thrown away the headroom that makes heavy retouching clean.

For a whole library, Photos on a Mac exports originals in bulk, and heif-convert or ImageMagick in a shell loop handles thousands of files with the EXIF kept.