GIF is a palette of at most 256 colours, all-or-nothing transparency, and animation. 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 GIF file on the way to becoming a HEIC one.
What runs when a GIF file becomes HEIC
ImageMagick 6.9.12, on a machine we rent and watch. Your GIF file is uploaded once, ImageMagick runs once, the HEIC comes back, and neither file is kept. GIF 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 GIF into the HEIC
The pixel dimensions of your GIF file. The HEIC comes out the size the GIF went in, because nothing on this path resizes anything.
What GIF to HEIC costs you
Every frame of the GIF but the first. GIF can hold an animation and HEIC cannot, so frame one is what comes back. The alternative would be one numbered HEIC file per frame and no single answer to hand you.
Exactness. HEIC is a lossy encoding, so the file you get back approximates the GIF you sent. The artefacts appear once and never come out again, which is why converting the HEIC back to GIF afterwards restores nothing.
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 GIF is mostly words, the useful move is to pull the text out of it, not to change which picture format holds it.
GIF to HEIC, measured rather than promised
Running GIF to HEIC against the real engine with a real file, ImageMagick wrote 5,402 bytes of HEIC in 0.1 seconds, machine otherwise idle. That is one GIF file on one day and not an average, which is why the number is given together with the file that produced it.
The GIF 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 GIF file, sent somewhere else
Other outputs the probe measured out of a GIF 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 GIF witness file.
GIF to PDF: 1,092,578 bytes in 0.9 seconds, verified by a format signature.
GIF to JPG: 20,559 bytes in under a tenth of a second, verified by a format signature.
GIF to PNG: 3,894 bytes in under a tenth of a second, verified by a format signature.
GIF to TIFF: 848,536 bytes in 0.2 seconds, verified by a format signature.
GIF to MP4: 54,682 bytes in 0.3 seconds, verified by ffprobe.
GIF to WEBM: 49,644 bytes in 2.0 seconds, verified by ffprobe.
Other ways into HEIC, and what they measured
Among the published routes into HEIC, GIF is the first largest output of the 10 measured. The witness files differ, so this ranks the probe run and not your document.
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.
TIFF to HEIC: 481 bytes in under a tenth of a second.
WEBP to HEIC: 579 bytes in under a tenth of a second.
What we will not pretend about GIF to HEIC
A GIF file over 25 MB is refused before the upload finishes rather than after it, so you do not wait for a rejection.
A GIF 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 GIF 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 5,402 bytes, recognised by a format signature.
No text is read out of the GIF 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 GIF to HEIC, not a marketing number.
One GIF file at a time, chosen in the browser. There is nothing else to set up and nothing else on offer.
GIF to HEIC: what people ask
What actually converts my GIF 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 GIF file is uploaded once, ImageMagick runs once, the HEIC comes back, and neither file is kept afterwards.
How long does GIF to HEIC take?
On the file the probe used, ImageMagick took 0.1 seconds and wrote 5,402 bytes of HEIC. That is one real measurement on one real GIF file, not an average and not a promise about yours: a larger GIF takes longer, and past 30 seconds the run is stopped.
What do I lose going from GIF to HEIC?
The one to know about first: Every frame of the GIF but the first. GIF can hold an animation and HEIC cannot, so frame one is what comes back. The alternative would be one numbered HEIC file per frame and no single answer to hand you.
My GIF is animated. Will the HEIC be?
No. A GIF can hold a whole sequence and a HEIC holds one image, so what comes back is the first frame. The alternative would be one numbered HEIC per frame, and there is no single file to hand you at the end of that.
Is GIF to HEIC free?
There is a free allowance every month, and one GIF 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.