HEIC vs JPEG: What Actually Changes When You Convert an iPhone Photo

Copy photos off an iPhone onto a computer and many of them end in .HEIC. Some apps open them, many do not, and websites that ask for “an image” often refuse them. Here is what the format is and what converting it costs.

What HEIC is

HEIC is a photo stored in the HEIF container, compressed with the same family of compression as HEVC (H.265) video. Apple made it the default iPhone camera format in iOS 11. The point is efficiency: a modern codec spends its bits more cleverly than JPEG, which dates from 1992, so a HEIC photo is typically around half the size of a JPEG that looks the same.

It can also hold things a JPEG cannot: more than 8 bits per colour, transparency, a depth map for portrait mode, and several images in one file.

Why so many things will not open it

Decoding HEVC-family images is not built into everything. Older Windows installations need an extra extension, many web services and online tools do not accept it, and outside Safari browser support is limited. That is why the same photo opens on your phone and fails on a website.

DiffALL’s tools are in that group today: they read JPG, PNG and WebP, not HEIC, and they say so when you pick a HEIC file rather than failing silently.

Ways to get a JPEG instead

• Upload from the iPhone itself. When a web page asks for a photo, Safari on iPhone converts HEIC to JPEG automatically as it uploads. The problem mostly appears on a computer the photos were synced to.
• Change the camera setting: Settings → Camera → Formats → Most Compatible makes new photos JPEG. Photos already taken stay HEIC.
• When transferring: Settings → Photos → Transfer to Mac or PC → Automatic converts as files are copied off.
• On a Mac: open in Preview → File → Export → JPEG.
• On Windows: the Photos app can open HEIC with the HEIF extension installed and save a copy as JPEG.

What converting costs

Converting is a re-encode: the HEIC is decoded to pixels and those pixels are compressed again as JPEG. Every lossy re-encode loses a little, and the amount is set by the JPEG quality you export at.

• At quality 90 or above, the loss is invisible at normal viewing size, and the file will be larger than the HEIC was — you are paying in bytes for compatibility.
• At quality 70 or below, blocking appears in skies and smooth gradients, and it becomes the weakest part of the photo.
• Extras that JPEG cannot hold — depth maps, more than 8-bit colour — are dropped.

If you are unsure what quality an export used, the image quality checker reads it back out of the JPEG itself and says whether compression is what is holding the photo back.

Which should you keep?

Keep the HEIC originals as your archive — they are the smaller, better source. Make JPEG copies for sharing, uploading and anything that has to open everywhere. Converting the other way, JPEG to HEIC, gains nothing: the JPEG damage is already baked in.