Why JPG isn't always the right target
Most guides about converting iPhone HEIC photos jump straight to JPG, and for everyday sharing that's the right call. But JPG re-compresses your photo with lossy encoding — fine for posting online, not ideal if the image is headed into a photo editor, a design project, or anything where every pixel of the original decode matters and you don't want another layer of compression stacked on top.
PNG is the format for exactly that case: it's lossless, meaning once the HEIC is decoded, nothing further is discarded when it's saved.
What "lossless" actually buys you here
The moment you convert a HEIC, you're already doing one lossy step in some sense — HEIC's own compression already happened at the moment the photo was taken. Converting to PNG doesn't undo that, but it guarantees no additional compression gets layered on top during the conversion itself. Convert the same photo to JPG instead, and you're adding a second round of lossy compression on top of the first.
For a photo you're about to retouch, crop precisely, or use as a base layer in a design tool, avoiding that second compression pass matters — small JPEG artifacts can become more visible after further edits like sharpening or heavy color adjustment.
The file size you're trading for that
PNG's losslessness isn't free — a PNG of a decoded HEIC photo will typically be noticeably larger than the equivalent JPG, sometimes several times the size, since you're keeping all the pixel data HEIC's efficient compression originally discarded room for. For a single photo this rarely matters; for a batch of dozens of high-resolution images, the size difference adds up fast.
If you're unsure which to pick: ask whether the image is a final deliverable for viewing (JPG is fine) or working material that's going through more editing steps (PNG protects that work).
The same primary-image detail applies here too
Like any HEIC conversion, it's worth knowing that an iPhone HEIC file often contains more than just your photo — a smaller embedded thumbnail typically rides along inside the same file for quick previews. A correct converter extracts the full-resolution primary image rather than that thumbnail, so the resulting PNG should match your camera's actual capture resolution.