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I googled whether HEIC images are lossless or lossy, and whereas some articles and forum threads insist HEIC images are lossy, other insist that HEIC supports both lossy and lossless compression,

but don't provide any details about how to use the latter. I use the latest Ventura, and when I edit HEIC images in Preview (and even if I chose "Lossless" when saving),

enter image description here

their quality degrade. My question is: How can I create lossless HEIC images, that is, the ones that won't degrade when I save and save them again and again?

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  • HEIC (like JPEG) is a mathematical approximation of the original image. If you need pixel-level accuracy, use TIFF or similar.
    – nohillside
    Commented Nov 6, 2023 at 6:36
  • @nohillside TIFF can have lossy compression, in fact, it can use JPEG. JPEG can be lossless. Don't get compression and container formats mixed up.
    – user71659
    Commented Nov 6, 2023 at 7:13
  • @user71659 Indeed it does, but AFAIK Preview doesn't use lossy compression when storing as TIFF.
    – nohillside
    Commented Nov 6, 2023 at 8:23
  • IIRC HEIC is just a frame of HEVC? Since HEVC support both lossy and lossless encoding HEIC also.
    – Joy Jin
    Commented Apr 24 at 15:56

2 Answers 2

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Found on Reddit:

HEIC is a lossless format

Wrong. HEIC is just a container (the C in the name is from Container). However in the way it is implemented by both Samsung and Apple for their pictures IT IS A LOSSY FORMAT with parameters set so as quality of compressed image is marginally better than that from JPG but at about half of the size of the JPG (and even for JPG you have a quality factor, which is usually in the 90-95% range).

https://reddit.com/r/GalaxyS23Ultra/comments/16fv6xu

So it seems the answer is that HEIC images can be either lossy or lossless, and both LinkedIn and Adobe articles seems to be misleading in this point. But currently the default macOS apps are using lossy HEIC, and to use lossless HEIC you need some professional software (not sure Photoshop does support it) or wait until macOS will use lossless HEIC instead of lossy.

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The HEIC images you are editing are very likely already compressed. The original information has already been lost. There is no way to get it back.

What you seem to look after is a way to prevent them from being further compressed after edition, not lossless.

Generally, it is not a good idea to edit jpeg/heic images if you want optimal quality. Compression algorithms are not made to hide your editions, and they will often appear, and result in what you call image degradation.

You should use the original lossless information if available (e.g RAW for cameras)

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