JPEG is lossy compression tuned for human vision, and no alpha channel at all. 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. ImageMagick sits between the two, and this page says exactly what happens to a JPG file on the way to becoming a HEIC one.
What runs when a JPG file becomes HEIC
ImageMagick 6.9.12, on a machine we rent and watch. Your JPG file is uploaded once, ImageMagick runs once, the HEIC comes back, and neither file is kept. JPG to HEIC 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 JPG into the HEIC
The pixel dimensions of your JPG file. The HEIC comes out the size the JPG went in, because nothing on this path resizes anything.
What JPG to HEIC costs you
Nothing measurable, which is rare enough to say plainly. JPG and HEIC carry the same kind of content with the same fidelity, so this pair changes the container and not the picture. What does change is the size, and often by a lot.
If a model is going to read the HEIC
A HEIC file is pixels, and pixels are expensive for a model to read. Handed this HEIC, an assistant spends its budget looking at the picture rather than reading it, and it will paraphrase what it thinks it saw. If your JPG is mostly words, the useful move is to pull the text out of it, not to change which picture format holds it.
JPG to HEIC, measured rather than promised
Running JPG to HEIC against the real engine with a real file, ImageMagick wrote 505 bytes of HEIC in under a tenth of a second, machine otherwise idle. That is one JPG file on one day and not an average, which is why the number is given together with the file that produced it.
The JPG to HEIC 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 HEIC file has anything inside it.
The same JPG file, sent somewhere else
Other outputs the probe measured out of a JPG file, so the cost of choosing HEIC can be read against something. Sizes do not compare across engines, because each family was probed with its own JPG witness file.
JPG to PDF: 4,232 bytes in under a tenth of a second, verified by a format signature.
JPG to PNG: 805 bytes in under a tenth of a second, verified by a format signature.
JPG to WEBP: 350 bytes in under a tenth of a second, verified by a format signature.
JPG to GIF: 3,487 bytes in 0.1 seconds, verified by a format signature.
JPG to TIFF: 72,264 bytes in under a tenth of a second, verified by a format signature.
Other ways into HEIC, and what they measured
Among the published routes into HEIC, JPG is the sixth largest output of the 10 measured. The witness files differ, so this ranks the probe run and not your document.
BMP to HEIC: 500 bytes in under a tenth of a second.
GIF to HEIC: 5,402 bytes in 0.1 seconds.
HEIF to HEIC: 486 bytes in under a tenth of a second.
ICO to HEIC: 807 bytes in 0.1 seconds.
SVG to HEIC: 1,009 bytes in 0.1 seconds.
What we will not pretend about JPG to HEIC
A JPG file over 25 MB is refused before the upload finishes rather than after it, so you do not wait for a rejection.
A JPG to HEIC 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 JPG to HEIC 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 HEIC it produced was 505 bytes, recognised by a format signature.
No text is read out of the JPG anywhere on this path. Converting a picture to HEIC 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 JPG to HEIC, not a marketing number.
One JPG file at a time, chosen in the browser. There is nothing else to set up and nothing else on offer.
JPG to HEIC: what people ask
What actually converts my JPG file to HEIC?
ImageMagick does it, 6.9.12, on a machine we rent and watch. Not a browser trick and not somebody else service: the JPG file is uploaded once, ImageMagick runs once, the HEIC comes back, and neither file is kept afterwards.
How long does JPG to HEIC take?
On the file the probe used, ImageMagick took under a tenth of a second and wrote 505 bytes of HEIC. That is one real measurement on one real JPG file, not an average and not a promise about yours: a larger JPG takes longer, and past 30 seconds the run is stopped.
What do I lose going from JPG to HEIC?
The one to know about first: Nothing measurable, which is rare enough to say plainly. JPG and HEIC carry the same kind of content with the same fidelity, so this pair changes the container and not the picture. What does change is the size, and often by a lot.
Does the HEIC come out the same size as the JPG?
The same pixel size, yes: nothing on this path resizes anything, so the HEIC is as wide and as tall as the JPG was. The number of bytes is a different question and usually moves a long way, which is normally the reason for doing this at all.
Is JPG to HEIC free?
There is a free allowance every month, and one JPG to HEIC 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 HEIC.