Orientation, colour and quality

2026-10-09

A HEIC photo from an iPhone carries more than pixels: which way is up, wide colour, sometimes 10 bits per channel and an extra image for HDR screens. A PDF can’t hold HEVC, the compression inside HEIC, so every photo is encoded again as a JPG on its way in. This guide explains what changes along the way, and what the two quality options do.

Which way is up

An iPhone doesn’t turn the picture when you hold the phone sideways. It saves the photo as the sensor saw it and records the rotation — in the HEIF container and again in the EXIF data. HEIC to PDF applies that rotation once, so a photo is never turned twice. We checked all eight orientations a file can record, mirrored ones included, in Chrome’s and Safari’s engines, and each came out correctly.

If a photo still lies on its side — a document photographed flat on a table is the usual case — tap Rotate 90° clockwise on its card, once for each quarter turn. The turn is applied when the photo is placed on its page; the pixels are not redrawn for it.

Colour: Display P3 becomes sRGB

iPhone photos use Display P3, a wider range of colours than standard sRGB, and they say so in an embedded colour profile. Before a photo goes into the PDF, its colours are converted to sRGB. We compared the result with LittleCMS, a widely used colour engine, and it matched: for example, P3 (200, 80, 60) becomes sRGB (216, 69, 50).

Some colours a P3 photo can hold don’t exist in sRGB: the most saturated reds and greens. Those are clipped to the nearest sRGB colour, so a very vivid flower or neon sign can look slightly less intense in the PDF than on a wide-colour screen.

10-bit photos and HDR

A 10-bit HEIC is stored with 8 bits per channel. The differences we measured were 1 or 2 levels out of 255 — too small to see in a photo.

iPhone HDR photos carry an extra “gain map” image for HDR screens. It is not used: the standard photo goes into the PDF.

Transparency

Transparency is rare in HEIC and doesn’t come from the iPhone camera. When a HEIC does have transparent areas, they become white, and its card says Transparent areas become white.

Quality first and Smaller file

Both options are in Page setup, and Details under them gives a short version of this section. With both, each photo is stored as a JPG.

* Photos above the device limit are scaled down with both options (see below).

† Smaller file uses its version only if that really makes the photo smaller in bytes; otherwise the photo keeps its Quality first version.

Smaller file never enlarges a photo, and long or wide images keep at least 600 px on their short side so that text in them stays readable.

We measured one 12-megapixel iPhone-style HEIC of 1.1 MB, 3024 × 4032 pixels:

• Quality first: a 1.9 MB PDF in Chrome, 2.6 MB in Safari’s engine. That is larger than the HEIC, because JPG needs more bytes than HEVC.
• Smaller file: the photo became 1500 × 2000 and the PDF 300 KB in Chrome, 594 KB in Safari’s engine.

How much your own PDF shrinks depends on your photos; there is no fixed percentage. Keep Quality first for photos you will print or zoom into, and choose Smaller file when the PDF has to fit an email or upload limit.

Very large photos

Your browser decodes every photo, and there is a device limit: images above 16,777,216 pixels (4096 × 4096) are scaled down to fit it, with either option. Their card says Scaled down to fit the device limit. A 48-megapixel iPhone photo (8064 × 6048) becomes 4729 × 3547; a 12-megapixel photo (4032 × 3024) fits without change. Photos over 134 megapixels are refused before they are opened, with a card asking you to add a smaller copy.

See the real size

After you tap Save PDF, the strip at the bottom shows the number of pages and the real file size. To compare, save once with Quality first, switch to Smaller file and save again. Combining HEIC photos into one PDF has the measured sizes for a batch of five.