HEIC vs JPG: What’s Actually Inside the File
If you copy photos from an iPhone or iPad to a computer, they often arrive as .heic files rather than .jpg. While both store photographs, their internal structures are completely different.
Need a JPG right now? Convert HEIC photos locally in your browser with the free HEIC to JPG converter.
How HEIC and JPG differ inside the bytes
A JPG (JPEG) file is a single compressed image stream wrapped in FF D8 FF … FF D9 markers, using DCT compression standardised in the early 1990s. Every web browser, photo editor and operating system can decode it directly.
A HEIC file is an ISO Base Media container (the same family of box-structured containers used by .mp4 and .mov video). Inside its ftyp header (66 74 79 70 68 65 69 63), a HEIC file holds:
- HEVC (H.265) encoded image tiles: High-resolution iPhone photos are often stored as a grid of dozens of smaller HEVC tiles plus a derived grid item (
grid) that tells the decoder how to stitch them into one seamless canvas. - Non-destructive rotation and mirroring boxes (
irot,imir): Instead of rotating the compressed tiles, the container stores container-level transform properties. - Wide-gamut colour profiles (
colr): iPhones capture photos in Display P3 colour, which covers roughly 25% more visible colour than standard sRGB. - Auxiliary images: Depth maps for Portrait mode, HDR gain maps, and alpha transparency channels (
auxl) can live alongside the primary photo inside the same.heiccontainer.
Why HEIC files are smaller for the same visual quality
HEVC compression uses modern block sizes and prediction modes that are roughly twice as efficient as classic JPEG compression. A 12-megapixel iPhone photo that takes 4 MB as a high-quality JPG often fits into 1.8–2.2 MB as a HEIC file with less visible banding in smooth skies and shadows.
Why renaming .heic to .jpg breaks the file
Changing IMG_1042.heic to IMG_1042.jpg in Finder or File Explorer only changes the filename label. The bytes inside still begin with an ISO Base Media ftyp box (00 00 00 … 66 74 79 70 68 65 69 63), not a JPEG FF D8 FF header.
Sometimes an app or cloud transfer service saves a HEIC file with a .jpg extension by mistake, causing older software on Windows or web upload forms to say the image is corrupt. You can spot a mislabelled HEIC photo immediately with the file type checker and read more in what a file extension mismatch means.
Converting HEIC to JPG without losing colour or privacy
When you convert a photo with the File Sniff HEIC to JPG converter:
- Each file is identified from its bytes (so a HEIC disguised as
.jpgstill converts properly). - Container transforms (
irot,imir) are applied once so the output JPG is always the right way up. - Where your browser supports wide-gamut canvases, Display P3 colour is preserved and an ICC Display P3 profile is embedded in the JPG.
- Location, camera serials and other EXIF metadata are left out of the new file. See how to remove EXIF and GPS metadata from photos.