Apple Log to Rec.709: what the conversion actually does

Why the clip looks flat

A camera sensor captures far more brightness range than a Rec.709 display can show. A Log curve squeezes that range into the file by spending code values logarithmically — many on the shadows and mid-tones, fewer on the highlights — so that a 10-bit file keeps detail from deep shade to bright sky. On a normal display this encoding looks grey, low-contrast and desaturated, because the display is showing the storage curve, not a picture.

Apple Log also records in a wide gamut (the file is tagged with Rec.2020 or Apple's own wide-gamut primaries), so colours are stored "smaller" than they will look after conversion. Nothing is wrong with the clip; it is simply not display-referred yet.

What the conversion LUT does

Apple's conversion table is a 65-point 3D LUT that maps Apple Log code values to Rec.709 display values. Three things happen inside it:

1. The Log curve is undone. Code values are expanded back toward scene brightness.
2. The gamut is mapped. Wide-gamut colours are brought into Rec.709 primaries.
3. A display rendering is applied. This is the part people miss: Apple's table is not a bare mathematical transform. It includes a tone curve with a highlight roll-off, so mid-grey lands brighter than a pure gamma-2.4 conversion would put it and skies do not clip abruptly.

Measured on a real clip, Apple's table renders 18 % grey at about 136 of 255 — roughly 53 % — and white at about 220 with around three stops of soft roll-off. A "technical" conversion (Log to linear, then a plain gamma 2.4) puts the same grey near 125 and clips highlights harder. Both are valid; they are different rendering intents.

Why two apps can show the same Apple Log clip differently

iOS hands every app the Log frames unconverted, even when the app asks for Rec.709. Each app therefore does its own conversion, and the choice of table decides the result. An app using Apple's official display rendering will look brighter and more filmic in the highlights; an app using a technical transform will look darker and more muted. Neither is a bug. LUTLINE uses Apple's published table, verified on device against the same cube applied on a Mac to the decoded code values, so the phone's render matches what a desktop tool produces with the same LUT.

Apple Log vs. Apple Log 2

iPhone 17 Pro introduced Apple Log 2, a revised curve with its own official conversion table. The two are not interchangeable: converting an Apple Log 2 clip with the Apple Log table shifts contrast and colour. LUTLINE keeps both tables and picks the right one from the clip's tags.

How to convert Apple Log in LUTLINE

Import the clip. The Source chip on the Adjust tab shows Auto · Apple Log (or Apple Log 2) — detected from the file's colour tags, not guessed from the file name. The conversion is applied on a 10-bit read path before any adjustment. From there, correct exposure and white balance, choose a look, and export; the preview and the export use the same conversion, so the file matches the screen.

When Auto shows "Standard" for a Log clip

Some transfers — messaging apps, certain cloud services, re-encodes — strip the colour tags that identify Apple Log. The picture is still Log, but the file no longer says so. Tap the Source chip and choose Apple → your iPhone → Apple Log. The choice is saved with the project.

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