HEIC is what an iPhone writes unless you tell it not to: HEVC compression inside an ISO container, about half the size of the JPEG it replaced. PNG is lossless compression with a full 8-bit alpha channel. ImageMagick sits between the two, and this page says exactly what happens to a HEIC file on the way to becoming a PNG one.
What runs when a HEIC file becomes PNG
ImageMagick 6.9.12, on a machine we rent and watch. Your HEIC file is uploaded once, ImageMagick runs once, the PNG comes back, and neither file is kept. HEIC to PNG is one of the 3649 pairs that engine was probed on with a real file, which is why it has a page here and why the pairs the probe could not prove do not.
What survives from the HEIC into the PNG
The pixel dimensions of your HEIC file. The PNG comes out the size the HEIC went in, because nothing on this path resizes anything.
Transparency. HEIC and PNG both carry a real alpha channel, so a cut-out sent as HEIC is still a cut-out as PNG.
What HEIC to PNG costs you
Every page of the HEIC but the first. A HEIC file can hold several images in one container; a PNG file holds exactly one.
Nothing further, and that is the point worth making: PNG cannot undo what HEIC already threw away. The compression artefacts are baked into the pixels, PNG stores them faithfully, and the file usually comes out several times larger for exactly the same picture.
If a model is going to read the PNG
A PNG file is pixels, and pixels are expensive for a model to read. Handed this PNG, an assistant spends its budget looking at the picture rather than reading it, and it will paraphrase what it thinks it saw. If your HEIC is mostly words, the useful move is to pull the text out of it, not to change which picture format holds it.
HEIC to PNG, measured rather than promised
Running HEIC to PNG against the real engine with a real file, ImageMagick wrote 1,403 bytes of PNG in under a tenth of a second, machine otherwise idle. That is one HEIC file on one day and not an average, which is why the number is given together with the file that produced it.
The HEIC to PNG verdict was reached by a format signature, meaning at least four bytes unique to the format were found at the right offset. Which check was used matters, because they do not all prove the same thing, and a status code of 200 proves nothing whatsoever about whether the PNG file has anything inside it.
The same HEIC file, sent somewhere else
Other outputs the probe measured out of a HEIC file, so the cost of choosing PNG can be read against something. Sizes do not compare across engines, because each family was probed with its own HEIC witness file.
HEIC to PDF: 94,782 bytes in under a tenth of a second, verified by a format signature.
HEIC to JPG: 1,666 bytes in under a tenth of a second, verified by a format signature.
HEIC to WEBP: 416 bytes in under a tenth of a second, verified by a format signature.
HEIC to GIF: 2,918 bytes in 0.1 seconds, verified by a format signature.
HEIC to TIFF: 90,264 bytes in under a tenth of a second, verified by a format signature.
Other ways into PNG, and what they measured
Among the published routes into PNG, HEIC is the fourth largest output of the 13 measured. The witness files differ, so this ranks the probe run and not your document.
JPG to PNG: 805 bytes in under a tenth of a second.
WEBP to PNG: 4,003 bytes in under a tenth of a second.
SVG to PNG: 1,268 bytes in under a tenth of a second.
GIF to PNG: 3,894 bytes in under a tenth of a second.
BMP to PNG: 810 bytes in under a tenth of a second.
What we will not pretend about HEIC to PNG
A HEIC file over 25 MB is refused before the upload finishes rather than after it, so you do not wait for a rejection.
A HEIC to PNG run that passes 30 seconds is killed, and the ImageMagick process is killed with it. A run left behind would sit on one of the machine's two cores until somebody noticed.
Until the end of August this machine could not read a HEIC at all, and reported the opposite. ImageMagick declared HEIC readable, but libheif carried only its AV1 plugins, which serve AVIF; the HEVC decoder was absent, and a HEIC decoded quietly as something else. The plugin was installed on the 30th, and that is the whole reason this pair exists.
The HEIC to PNG proof used a file genuinely encoded in HEVC, and that detail is not pedantry: ImageMagick refuses to write HEIC and hands you a PNG under that name if you ask it to, so a HEIC forged for the test would have made a false result look like a true one. The PNG it produced was 1,403 bytes, recognised by a format signature.
No text is read out of the HEIC anywhere on this path. Converting a picture to PNG never turns it into words, whatever the picture happens to contain.
ImageMagick was not saturated at sixteen simultaneous conversions: it held 47.5 a second while latency moved from 0.22 s to 0.34 s, and the service memory did not move off 51 MB. That is the measured headroom behind HEIC to PNG, not a marketing number.
One HEIC file at a time, chosen in the browser. There is nothing else to set up and nothing else on offer.
HEIC to PNG: what people ask
What actually converts my HEIC file to PNG?
ImageMagick does it, 6.9.12, on a machine we rent and watch. Not a browser trick and not somebody else service: the HEIC file is uploaded once, ImageMagick runs once, the PNG comes back, and neither file is kept afterwards.
How long does HEIC to PNG take?
On the file the probe used, ImageMagick took under a tenth of a second and wrote 1,403 bytes of PNG. That is one real measurement on one real HEIC file, not an average and not a promise about yours: a larger HEIC takes longer, and past 30 seconds the run is stopped.
What do I lose going from HEIC to PNG?
The one to know about first: Every page of the HEIC but the first. A HEIC file can hold several images in one container; a PNG file holds exactly one.
My HEIC holds more than one image. Which one comes back?
The first. A HEIC file can carry several images in one container and a PNG file carries exactly one, so the engine takes the first rather than inventing a way to give you the rest.
Is HEIC to PNG free?
There is a free allowance every month, and one HEIC to PNG conversion costs half a credit against it. When the allowance runs out the tool says so and stops, rather than quietly handing you a worse PNG.