Where HEIC’s savings come from
JPEG, standardised in 1992, splits every image into a grid of 8 × 8 pixel blocks, converts each block into frequencies and throws away the fine ones it thinks you won’t notice. Every block costs roughly the same overhead, even in an empty sky.
HEVC was designed two decades later for video. It uses blocks as large as 64 × 64 where the picture is smooth and splits down to 4 × 4 where there’s texture. It also predicts each block from its already-decoded neighbours in 35 directions and only stores the difference. Together that is why a HEIC is typically about half the size of a JPG at the same visual quality.
That cleverness costs compatibility. HEVC is covered by patent pools, so many operating systems and apps have avoided shipping a decoder by default. JPEG’s patents expired long ago, which is why it opens everywhere.
Wanting to know where half the file actually went is a good instinct; ahaboo answers that sort of why-question with narrated explainers, such as why the Moon has phases.
Which should you use?
- Keep HEIC on the phone and in your iCloud or Apple Photos library: smaller, higher quality, metadata intact.
- Convert to JPG whenever the photo leaves Apple devices: email to a Windows user, upload forms, print shops, marketplaces.
- Convert to PNG only if you’ll edit the photo repeatedly and want no further loss.