What is the difference between LogC3 and LogC4?

LogC3 is the encoding used by ALEXA cameras up to the Mini LF, and by AMIRA, on the ALEV3 sensor. LogC4 is the encoding for the ALEXA 35 and newer, on ALEV4, created because 17 stops of dynamic range cannot be contained in LogC3. LogC4 encodes some content, including skin tones, darker and with less contrast: 18% grey lands at 28% signal in LogC4 against 39% in LogC3. The two are not interchangeable, and LogC3 LUTs must not be used on LogC4 footage.

Does the ARRI LUT depend on the EI I shot at?

On LogC3, yes. The LogC3 curve changes with the exposure index, so correct linearisation depends on knowing the EI, and a LUT built at the wrong EI puts the whole tone scale off. ARRI's online LUT Generator builds a LogC3 LUT for a specific EI. LogC4 is different: the LogC4 curve is exposure index independent, so correct decoding does not depend on the EI the operator selected.

Which LUT converts LogC4 to Rec.709?

ARRI's official display render transform, named ARRI_LogC4-to-Gamma24_Rec709-D65_v1, from the ARRI LogC4 LUT package. ARRI's LUT names read source-to-target, so the filename states exactly what the transform does. The package also includes HDR transforms, one of which outputs HLG at a 203-nit diffuse white to meet ITU-R BT.2408 for broadcast.

Why does my LogC4 footage look underexposed?

Because LogC4 encodes darker than LogC3 by design, to make room for the ALEXA 35's extra highlight latitude — ARRI notes that viewed directly, LogC4 might seem underexposed. Judge exposure through the display transform or on a waveform against the LogC4 anchors, not by eye on the raw log image.

Can I reuse a LogC3 show LUT on an ALEXA 35?

ARRI advises redesigning or visually rematching a LogC3-based show LUT for cameras using REVEAL colour science rather than reusing it. For LogC4, a Look Library look is applied log-to-log and must be combined with the official display render transform — the look alone is not a complete conversion.

07 · Reference · ~5 minute read · updated Aug 2026

ARRI LUTs Guide

LogC3 or LogC4, which display transform to use, and the one thing that catches everybody out: on LogC3 the curve itself changes with the EI you shot at. On LogC4 it doesn't.

Not sure what any of the terms below mean? Skip straight to the confidence check — it tells you if your footage is fine without needing to understand why.

This guide covers both ARRI ProRes and ARRIRAW. ProRes can hold everything an ARRIRAW frame carries in the same colour space, so for a lot of jobs it is the sensible recording format; ARRIRAW is for when the finish justifies the storage and the post time. Switch between them at the top of the workflow builder below.

If you're producing

The decision that matters before the shoot is which encoding the show is finishing in — and on a mixed ARRI rig, that decision has a direction: legacy ARRIRAW can be brought up into LogC4, but LogC4 cannot be pushed back into LogC3. Settle it in the workflow builder and export it as a PDF for whoever grades.

If you're editing or grading

Jump straight to building the workflow — pick the encoding, the delivery transform and your app, for a step-by-step setup plus a printable sheet.

The easy confidence check

Which LogC am I holding?

ARRI LOG C ↗

It's decided by the camera, not a menu setting, so this is the one question with a clean answer. ALEXA 35, 35 Xtreme and 265 record LogC4 in ARRI Wide Gamut 4. Everything up to and including the ALEXA Mini LF, plus AMIRA, records LogC3 in ALEXA Wide Gamut. Get the camera model off the call sheet or the clip metadata and you have your answer — no guessing, and no LUT should ever cross that line.

If it's LogC3, find the EI before you do anything else

This is the ARRI-specific trap. The LogC3 curve changes with the exposure index set in camera, so a LUT is only correct at the EI it was built for — get it wrong and the tone scale is off across the whole image, in a way that looks like a grading choice rather than a mistake. The EI should be in the camera reports; if it isn't, ARRI's online LUT Generator will build a LogC3 LUT for whichever EI you can establish. LogC4 removes this problem entirely — the curve is exposure-index independent, so the same decode is correct at any EI. Grey and clip values per camera and EI are in the exposure & log reference.

Build your workflow

This part's for whoever is setting up the edit — an editor, DIT or colourist. Pick the encoding, the delivery transform and the app, and it'll lay out the exact steps — plus a printable sheet you can hand off.

ProRes (LogC)

ARRIRAW

+ Show technical detail (curves, gamuts, LUT internals)

+ Planning before the shoot? See pros & cons of each stage

For deciding before you roll — weigh these before you commit the show to an encoding.

STAGE 1 — CAMERA + LOG ENCODING

LogC3 (ALEXA up to Mini LF, AMIRA)

ADVANTAGE

Two decades of shows graded on it. Every colourist knows the curve, and every existing show look already speaks it.

TRADE-OFF

The curve changes with EI, so a LUT only reads correctly at the EI it was built for — the biggest source of ARRI post confusion.

LogC4 (ALEXA 35, 35 Xtreme, 265)

ADVANTAGE

Exposure-index independent, which removes the whole class of LogC3 EI mistakes, and it holds the ALEXA 35's 17 stops.

TRADE-OFF

Darker and flatter on a monitor — ARRI notes it can seem underexposed. LogC3 show LUTs do not carry over.

Legacy ARRIRAW debayered to LogC4

ADVANTAGE

Lets a mixed rig finish as one grade — older ARRIRAW can be brought into a REVEAL pipeline via the ARRI Image SDK.

TRADE-OFF

One-way only. LogC4 material cannot be moved into a LogC3 pipeline, so the direction has to be decided before the show starts.

STAGE 2 — LUT / DELIVERY TARGET

Rec.709 DRT

ADVANTAGE

ARRI's official display render transform — the standard viewing and delivery conversion for HD.

TRADE-OFF

It is a display transform, not a look. If the show wants a look, that sits on top of it.

HDR — PQ or HLG

ADVANTAGE

ARRI ships both, and the HLG transform uses a 203-nit diffuse white so the result meets BT.2408 for broadcast.

TRADE-OFF

Only if the delivery specifies HDR, and it needs an HDR monitor to judge properly.

Look Library or a show look

ADVANTAGE

Gives the production a house image everyone monitors against, from the first day.

TRADE-OFF

On LogC4 the look is log-to-log and must be combined with the DRT — one without the other is simply wrong.

No LUT — grade natively

ADVANTAGE

The whole point of ARRIRAW. Everything the sensor saw, still on the table.

TRADE-OFF

Slowest route, and it needs correct colour management from the first day of dailies.

STAGE 3 — EDIT APP

Premiere Pro

ADVANTAGE

Handles ARRI ProRes cleanly and reads the log tag on most current media.

TRADE-OFF

ARRIRAW needs its source settings checked by hand.

DaVinci Resolve

ADVANTAGE

First-class ARRI support — LogC3 and LogC4 are both native input transforms, and the mixed-format case is well trodden.

TRADE-OFF

Still needs the EI checked per clip on LogC3 material.

Final Cut Pro

ADVANTAGE

Clean per-clip camera LUT handling for ARRI footage.

TRADE-OFF

Fewer manual overrides than Resolve, and Mac-only.

Avid Media Composer

ADVANTAGE

The standard on episodic drama, which is where most ARRI footage ends up.

TRADE-OFF

Set every clip explicitly, or bake in at transcode.

Downloads

ARRI LogC4 LUT package

ARRI DOWNLOADS ↗

The official display render transforms for ALEXA 35 and newer, including Rec.709 and the HDR transforms — one of which outputs HLG at a 203-nit diffuse white to meet ITU-R BT.2408.

ARRI LogC3 LUT package

ARRI DOWNLOADS ↗

For ALEXA cameras up to Mini LF and AMIRA. For a LUT built at a specific exposure index, use ARRI's online LUT Generator instead of the generic package file.

LUT naming convention — LogC4 and LogC3

PDF ↗

ARRI's own guideline to what the filenames mean. Worth five minutes: the names read source-to-target, so once you can parse one you can tell at a glance whether a LUT belongs on your footage.

LogC4 specification

PDF ↗

The formal definition of the curve and ARRI Wide Gamut 4 — including the statement that LogC4 is exposure index independent, and why that differs from LogC3.

One line from ARRI's own guideline is worth repeating: all their 3D LUTs are designed for Full Range input and output, so the whole pipeline has to stay Full Range. Most devices convert Legal Range correctly on input; some don't. Verify it before you trust what the blacks are doing.

Common hiccups

Tap one open — the first is the one that costs people afternoons.

A LogC3 LUT used at the wrong EI

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The LogC3 curve is exposure-index dependent: the encoding itself changes with the EI set in camera, so correct linearisation needs to know that value. Apply a LUT built at a different EI and the tone scale is wrong across the whole image — but wrong in a smooth, plausible way that reads as a grading decision rather than an error, which is exactly why it survives all the way to a review. Get the EI from the camera reports, and use ARRI's LUT Generator to build for that EI. LogC4 removes the problem: the curve is EI-independent by design, which ARRI describes as a notable change from LogC3.

Legal range somewhere in the chain

ARRI's 3D LUTs are built for Full Range in and Full Range out, and ARRI is explicit that processing must take place entirely in Full Range. Most devices convert a Legal Range signal correctly on input — some don't, and the result is crushed blacks and clipped whites that look like an exposure problem rather than a plumbing one. Check the range setting on every box in the chain, not just the software.

Judging a wireless video feed without the decoding LUT

A set-side one. Wireless transmitters are built for high-contrast Rec.709-like signals, so ARRI provides a Wireless Video Optimized LogC4 encoding for SDI transmission — and a WVO image without its decoding LUT is not compatible with any LogC4 LUT or with false colour. ARRI's own warning is blunt: judging images without the decoding LUT will mislead and could result in serious exposure issues. If the video village picture and the camera's own monitor disagree, this is usually why.

Mixing LogC3 and LogC4 on one show

Common the moment an ALEXA 35 joins a Mini LF. The conversion runs one way: ARRIRAW from Mini LF, Mini and ALEXA 65 can be debayered into LogC4 with the ARRI Image SDK, but LogC4 material cannot be moved into a LogC3 pipeline. So the show's working space has to be decided at the start, not discovered in the grade — and ARRI publishes a workflow guideline specifically for grading a mixed job.

Reusing a LogC3 show LUT on an ALEXA 35

Tempting on a returning series, and ARRI's advice is not to: a LogC3-based show LUT should be redesigned or visually rematched for cameras using REVEAL colour science. Related, and easy to get half-right — a Look Library look for LogC4 is applied log-to-log, so it has to be combined with the official display render transform. The look on its own is not a complete conversion.

More tools

01a · Data

ARRI Data Calculator

ARRIRAW and ProRes file sizes per hour.

Open

03 · Exposure

Exposure & Log Reference

IRE, false colour and log zones per camera.

Open

06 · Reference

Sony LUTs Guide

The same guide for S-Log3 footage.

Open

07 · Reference

ARRI LUTs Guide

LogC3 vs LogC4, the EI trap, and which transform to use.

You're here

Written by Keith Ingram, Glasgow-based Director of Photography.

Need a DoP for the shoot itself, not just the LUTs afterward? See Director of Photography services — Glasgow-based, available across Scotland, the UK and worldwide.