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. TIFF is lossless, alpha, and several images inside a single file. ImageMagick sits between the two, and this page says exactly what happens to a HEIC file on the way to becoming a TIFF one.
What runs when a HEIC file becomes TIFF
ImageMagick 6.9.12, on a machine we rent and watch. Your HEIC file is uploaded once, ImageMagick runs once, the TIFF comes back, and neither file is kept. HEIC to TIFF 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 TIFF
The pixel dimensions of your HEIC file. The TIFF comes out the size the HEIC went in, because nothing on this path resizes anything.
Transparency. HEIC and TIFF both carry a real alpha channel, so a cut-out sent as HEIC is still a cut-out as TIFF.
What HEIC to TIFF costs you
Nothing further, and that is the point worth making: TIFF cannot undo what HEIC already threw away. The compression artefacts are baked into the pixels, TIFF 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 TIFF
A TIFF file is pixels, and pixels are expensive for a model to read. Handed this TIFF, 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 TIFF, measured rather than promised
Running HEIC to TIFF against the real engine with a real file, ImageMagick wrote 90,264 bytes of TIFF 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 TIFF 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 TIFF 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 TIFF 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 PNG: 1,403 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.
Other ways into TIFF, and what they measured
Among the published routes into TIFF, HEIC is the fourth largest output of the 10 measured. The witness files differ, so this ranks the probe run and not your document.
HEIF to TIFF: 90,264 bytes in under a tenth of a second.
ICO to TIFF: 96,278 bytes in under a tenth of a second.
SVG to TIFF: 2,464 bytes in under a tenth of a second.
WEBP to TIFF: 72,264 bytes in under a tenth of a second.
PNG to TIFF: 1,466 bytes in under a tenth of a second.
What we will not pretend about HEIC to TIFF
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 TIFF 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 TIFF 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 TIFF it produced was 90,264 bytes, recognised by a format signature.
No text is read out of the HEIC anywhere on this path. Converting a picture to TIFF 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 TIFF, 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 TIFF: what people ask
What actually converts my HEIC file to TIFF?
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 TIFF comes back, and neither file is kept afterwards.
How long does HEIC to TIFF take?
On the file the probe used, ImageMagick took under a tenth of a second and wrote 90,264 bytes of TIFF. 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 TIFF?
The one to know about first: Nothing further, and that is the point worth making: TIFF cannot undo what HEIC already threw away. The compression artefacts are baked into the pixels, TIFF stores them faithfully, and the file usually comes out several times larger for exactly the same picture.
Why is the TIFF bigger than the HEIC it came from?
Because HEIC is a lossy encoding and TIFF is not. The HEIC reached its size by throwing detail away; TIFF stores every pixel it is handed, compression artefacts included, so the same picture comes back several times larger. Nothing was added and no quality was recovered.
Is HEIC to TIFF free?
There is a free allowance every month, and one HEIC to TIFF 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 TIFF.