The Compression Lab
This 3D surface is a stand-in for a 12-megapixel photo (4032 × 3024 px). Each block is a region of the image; block height is detail. Lower the quality slider and watch compression merge fine detail into coarse blocks — that's the "blockiness" you see in over-compressed images. Switch formats to compare estimated file sizes.
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Why HEIC wins on size — and loses on compatibility
HEIC (High Efficiency Image Container) stores a photo using HEVC/H.265 — the same math that compresses 4K video. It uses smarter block prediction and larger, flexible block sizes than JPG's 1992-era 8×8 DCT grid, so it keeps more detail per byte. The uncompressed 12MP frame is about 36.6 MB of raw pixel data (4032 × 3024 × 3 bytes). Typical results:
| Format | Year | Typical 12MP size | Compression | Works everywhere? |
|---|---|---|---|---|
| HEIC | 2015 | ≈ 1.7 MB | Lossy, ~20:1 | No — patchy on web & older Windows |
| JPG | 1992 | ≈ 3.4 MB | Lossy, ~10:1 | Yes — the universal default |
| PNG | 1996 | ≈ 15–25 MB | Lossless | Yes — but huge for photos |
HEIC also supports 10-bit color, transparency, and stores Live Photos and burst sequences in one container. JPG supports none of that — but every browser, printer kiosk and government upload form since the Clinton administration accepts it.
Three ways to convert on iPhone
1 · The Shortcuts recipe (batch converter)
- Open Shortcuts → tap + to create a new shortcut.
- Add action "Select Photos" and enable Select Multiple.
- Add action "Convert Image" → set format to JPEG.
- Add action "Save to Photo Album" (or "Save File" for Files app).
- Name it "HEIC → JPG" — it now batch-converts any selection in one tap.
2 · Stop shooting HEIC entirely
Settings → Camera → Formats → Most Compatible. New photos save as JPG (files roughly double in size).
3 · Let transfer do it automatically
Settings → Photos → Transfer to Mac or PC → Automatic. iPhone converts to JPG on the way out via USB. Emailing or AirDropping to non-Apple targets usually converts too.