ARRI Alexa files in post-production: technical guide

Table of Contents

Introduction: The ARRI Philosophy

Unlike the pixel race, ARRI prioritizes photosite size (for sensitivity and noise) and Dynamic Range. The challenge in post-production is never to limit this latitude. The ALEXA produces a 'thick' and robust image that is very forgiving, but requires a processing chain respectful of LogC colorimetry.

ARRI ALEXA Native Formats

ARRI ALEXA Pipeline

• Shooting (ALEXA / Mini / 35)
• Secure Offload (xxHash)
• Editing (ProRes / Proxy)
• Conform (XML/AAF)
• Grading (LogC / RAW)
• Mastering (DCP / PAD)

ALEXA File Architecture

ARRI metadata is rich. Timecode is absolutely precise (never drifts). Files contain embedded 'Look Files' (CDL/3D LUT) used on set, allowing the cinematographer's intent to be retrieved instantly.

ALEXA Media Preparation

• 1Security: Copy with xxHash Checksum verification (Silverstack, Hedge, Yoyotta).
• 2Directory Structure: Keep ARRI card structure (A001R1JC...). Never rename source clips.
• 3Verification: Open a few shots in ARRI Reference Tool to verify metadata integrity.

Editing ALEXA Files

ARRI Color Science

Understanding LogC is vital. Since ALEXA 35, we have two standards:

LogC3 (Classic) Standard gamma curve for ALEXA Mini, AMIRA, LF. ARRI Wide Gamut (AWG3) color space.

LogC4 (Alexa 35) New curve to manage 17 stops of dynamic range. AWG4 color space. Warning: LogC3 LUTs do NOT work on LogC4.

ACES ARRI provides official IDTs perfect for the ACES workflow.

Image Continuity: From Set to Grade

ALEXA allows creating 'Looks' (.alf4 / .aml) on set. These looks travel in metadata. In post-production, extract this metadata to apply as a starting point in grading, respecting the D.O.P.'s vision.

Grading Stage: ALEXA Specifics

Highlight Management

ARRI's 'Roll-off' is legendary for its smoothness. In grading, use soft mapping tools to avoid brutally 'clipping' this transition to white.

Texture & Noise

ALEXA noise is very organic, close to film grain. Avoid over-smoothing (excessive Denoise) or the image will look 'plastic'.

Deliverables & Mastering

Thanks to source quality, an ALEXA master can be effortlessly derived into HDR (Dolby Vision / HDR10) and SDR Cinema (DCI-P3) or Broadcast (Rec.709).

Professional Best Practices

DO

• • Always ask the D.O.P which Log (C3 or C4) was used.
• • Check frame rate (Project Rate vs Sensor FPS) for slow motion.
• • Use ARRI Color Tool to preview Looks.

DON'T

• • Never apply a basic 'Rec709' LUT on LogC4 without checking source.
• • Do not manually mix AWG3 and AWG4 color spaces.
• • Do not delete .xml files accompanying ARRIRAW clips.

Technical FAQ

ForCut Studio Approach

Our workstations are calibrated for the ARRI workflow. We have the latest ARRI LUTs (including REVEAL for Alexa 35) and the computing power needed for real-time ARRIRAW debayering.

Conclusion

"The ARRI ALEXA image is a raw gem. A rigorous post-production workflow is the only way to cut this diamond to reveal its full brilliance on the big screen."