ARRI LogC4 is the fourth-generation logarithmic image encoding introduced with the ALEXA 35 and REVEAL Color Science.
Log-C4 (ARRI's spelling: LogC4) is ARRI's fourth-generation logarithmic encoding curve. It was specified in 2022 and introduced with the ALEXA 35 and the associated REVEAL Color Science. LogC4 is the direct successor to LogC3, which ARRI has used since 2011, and continues its version history. LogC4 is not lighting or grip equipment, but rather camera and post-production encoding: it describes how the sensor's brightness values are converted into a storable, logarithmically compressed signal that maps the camera's high dynamic range into a file.
LogC4 is closely linked to the ARRI Wide Gamut 4 (AWG4) color space. AWG4 is fully contained within the ACES-AP0 color space and has a similar volume to ACES AP1, while avoiding invisible colors. When referring to "LogC4 material," it typically means the combination of the LogC4 curve and the AWG4 color space.
The central difference to LogC3 is EI independence: the LogC4 curve can be linearized with the exact same function, independent of the Exposure Index (EI) set in the camera. With LogC3, the curve changed depending on the EI setting. This simplifies decoding in post-production.
According to ARRI, the ALEXA 35 sensor (ALEV 4) achieves a dynamic range of 17 stops; the LogC4 curve was developed to meaningfully accommodate this extended range in encoding.
LogC4 is used by ARRI cameras with the ALEV-4 sensor generation. Current ARRI software can also decode ARRIRAW material from other models to LogC4.
| Aspect | LogC3 | LogC4 |
|---|---|---|
| Introduced | 2011 | 2022 (ALEXA 35) |
| Middle Gray (Codeword) | approx. 39% | approx. 32% |
| EI Dependency | yes | no |
| Color Space | ARRI Wide Gamut | ARRI Wide Gamut 4 |
| Look Format | ALF-2 | ALF-4 |
On set, LogC4 is primarily relevant for DITs and post-production. The "Log-to-Log" principle introduced with ALF-4 separates creative color decisions from the output transform: the ALF-4 look remains independent of SDR or HDR output, allowing simultaneous SDR and HDR monitoring on separate SDI outputs. When shooting with mixed camera parks (LogC3 and LogC4), it should be noted that both encodings are not identical; ARRI provides its own workflow guidelines and LUTs for this purpose.
Ich nutze Log-C4 hauptsächlich für die erweiterte Schattenzeichnung bei Available-Light-Szenen – die 1,5 Blendenstufen weniger Rauschen geben mir deutlich mehr Flexibilität bei ISO 3200 aufwärts. Der erweiterte Farbraum macht sich besonders bei LED-Panels bemerkbar, wo ich früher mit Log-C3 Clipping in den Rottönen hatte.
Log-C4 erlaubt mir extremere Lichtsituationen ohne Kompromisse bei der visuellen Erzählung – Kerzenlicht-Szenen behalten ihre Intimität, während gleichzeitig Details in den Schatten lesbar bleiben. Die präziseren Hauttöne geben mir mehr Spielraum für emotionale Farbgestaltung im Grading, ohne dass Gesichter unnatürlich wirken.
Log-C4 erfordert 30% mehr Speicherkapazität und verlängert die Post-Production um etwa zwei Tage pro Dreiwoche, rechnet sich aber durch weniger Nachbeleuchtung am Set. Die Netflix-Qualifikation öffnet Premium-Budgets, während die reduzierten Lighting-Kosten das höhere Datenvolumen kompensieren.
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