--- title: "The Alexa 35 13-Bit ARRIRAW Problem: Why ProRes 4444 Is Not Enough and What to Do About It" author: "Cutsio Team" date: "2026-05-08" lastmod: "2026-05-08" category: "Storage & Performance" excerpt: "Learn why Alexa 35 13-bit ARRIRAW exceeds ProRes 4444's 12-bit capacity, how to build an EXR-based VFX pipeline that preserves the full sensor data, and where cloud dailies fit in a high-bit-depth workflow." tags: ["ARRI RAW","Alexa 35","13-bit","ARRIRAW","EXR","ProRes 4444","VFX Pipeline","Color Pipeline","Post Production","ACES","LogC4"] --- ## Why does Alexa 35 13-bit ARRIRAW break ProRes 4444 and what is the correct workflow? The Alexa 35 records 13-bit log ARRIRAW data from its ALEV4 sensor, which processes images in 18-bit linear space internally. Apple ProRes 4444 and ProRes 4444 XQ support up to 12-bit color depth, so they are not equivalent containers for the full 13-bit ARRIRAW signal. For VFX and high-end color work that needs the camera original latitude, the safer workflow is to debayer ARRIRAW from the source and render 16-bit float OpenEXR (EXR) plates in a scene-linear working space such as Alexa Wide Gamut scene-linear or ACEScg. This is not a theoretical concern. Post houses and VFX facilities receiving Alexa 35 ARRIRAW footage can run into the problem when a standard ProRes 4444 mezzanine pipeline becomes the working source. ProRes will accept the transcode without warning, but the 13-bit log ARRIRAW signal has been represented with fewer code values before VFX work begins. The risk is not that the file becomes unusable; the risk is that subtle highlight gradation and recovery headroom are reduced before compositing or finishing. The Alexa 35 uses the ALEV4 sensor with 17 stops of dynamic range. ARRIRAW records this as 13-bit log data after ARRI's internal 18-bit linear image processing. Alexa 35 ProRes recordings are 12-bit LogC4, which is excellent for many editorial and grading workflows but is still not the same as retaining the 13-bit ARRIRAW source for VFX plates. Working with raw camera footage? Check out [How to Build a Searchable Library From ARRIRAW, RED R3D, and ProRes Footage](/blog/how-to-build-searchable-library-from-arriraw-red-r3d-prores-footage). ## What is the correct EXR pipeline for Alexa 35 13-bit ARRIRAW? The correct pipeline converts ARRIRAW to 16-bit float OpenEXR in a scene-linear working space such as Alexa Wide Gamut scene-linear or ACEScg. The EXR does not create new image information; it gives VFX a floating-point container that can represent the debayered camera data without forcing it into a 12-bit ProRes mezzanine. | Step | Action | Format | Bit Depth | Result | | :--- | :--- | :--- | :--- | :--- | | 1 | Debayer ARRIRAW in DaVinci Resolve or ARRI Reference Tool | ARRIRAW to RGB | 13-bit log to 16-bit float | Full sensor data preserved | | 2 | Convert to scene-linear working space | Alexa Wide Gamut / ACEScg | 16-bit float | Linearizes the log data for VFX | | 3 | Render EXR image sequence | OpenEXR (PIZ compression) | 16-bit float | Edit-friendly VFX plate | | 4 | VFX work in Nuke, Flame, or After Effects | OpenEXR | 16-bit float | Full latitude for comp work | | 5 | Deliver graded EXR or ProRes 4444 for finish | As required | 16-bit float or 12-bit | Final output matches source quality | The key principle: convert to a scene-referred linear working space before EXR export, not a display-referred space. ACEScg and Alexa Wide Gamut are both appropriate scene-referred spaces. Exporting to EXR in LogC4 or any log-encoded space defeats the purpose because the log encoding compresses the highlight data in a way that is not ideal for VFX compositing. ## How does the 13-bit problem manifest differently for VFX versus grading? The problem affects VFX and grading workflows differently, and the solution is not the same for both. For color grading, the impact is less severe. Most colorists work in ACES or DaVinci Wide Gamut within Resolve, where the ARRIRAW source is debayered and processed in floating-point precision throughout the grading pipeline. The 13-bit log data is only truncated if the colorist renders a ProRes 4444 mezzanine from the ARRIRAW source for an external workflow — for example, sending a graded reference to a client review platform or creating a proxy for an offline edit. For VFX, the problem is acute. VFX compositing applications like Nuke and Flame work best with scene-linear EXR plates. If the VFX house receives ProRes 4444 transcodes instead of EXR, they lose the highlight detail before any compositing work begins. Keying, grain matching, and CG integration all suffer when the working plate has already been truncated to 12 bits. The practical distinction: grading workflows can stay entirely within Resolve's floating-point processing and never hit the 12-bit ceiling. VFX workflows require EXR output from the ARRIRAW source, and that output must be created deliberately — it will not happen automatically from a standard ProRes proxy pipeline. ## Where does the ProRes 4444 limitation actually cause visible problems? The 12-bit ceiling in ProRes 4444 can manifest as highlight quantization, especially after strong grading or VFX operations. In practical terms, a sky gradient that the Alexa 35 sensor captured with smooth 13-bit log gradation may have fewer tonal steps once rendered through a 12-bit ProRes 4444 pipeline. This is most noticeable in: - Smooth sky gradients with subtle cloud detail - Skin tones in bright key light with highlight roll-off - Practical light sources with smooth falloff - White garments with textural detail in the highlights - Any scene with a wide exposure range that uses the sensor's full latitude A 12-bit encoding stores 4,096 code values per channel. A 13-bit encoding stores 8,192 code values per channel. When the 13-bit ARRIRAW signal is represented in a 12-bit mezzanine, the available code values are reduced before downstream operations. Whether the difference is visible depends on the shot, the transform, and the grade, but VFX plates should avoid that avoidable reduction. ## How do cloud dailies fit into a 13-bit ARRIRAW pipeline? Cloud dailies operate separately from the VFX mezzanine pipeline. The review stream is a viewing proxy, not a working master. Cutsio generates streamable review assets from the native ARRIRAW files using the correct LogC4-to-video color transform, and the original 13-bit ARRIRAW files remain attached as downloadable attachments. The separation of concerns: - **Review stream**: Optimized for viewing, not for VFX work. The director and DP see a correctly-logged image in the browser player. - **Original ARRIRAW**: Always available for download. The full 13-bit log data is preserved in the original .ari or .mxf file. - **EXR pipeline**: The VFX house downloads the original ARRIRAW and generates 16-bit float EXR plates directly from the source. This means the production does not need to choose between a usable review workflow and a technically correct VFX pipeline. The review stream serves the director, editor, and producers. The EXR plates serve the VFX and finishing teams. Both derive from the same native ARRIRAW source. ## What happens when you convert 13-bit ARRIRAW to 16-bit float EXR? Converting 13-bit log ARRIRAW to 16-bit float EXR in a scene-linear working space does not add information. It represents the debayered camera data in a floating-point format that is standard for compositing, relighting, CG integration, and image-processing operations. The benefit is workflow precision and VFX compatibility, not invented dynamic range. The EXR conversion pipeline: 1. Debayer the ARRIRAW using the correct ARRI debayer algorithm (ADA-7 or later) 2. Convert from LogC4 encoding to scene-linear (AWG or ACEScg) 3. Export as 16-bit float EXR with PIZ compression 4. The resulting EXR file contains the full sensor data in a VFX-ready format EXR PIZ compression is lossless for 16-bit float image data. File-size savings vary by image content, but PIZ is commonly used for VFX plates because it reduces storage compared with uncompressed EXR while preserving the encoded pixel values. ## FAQ ### Does ProRes 4444 XQ solve the 13-bit problem? No. ProRes 4444 XQ increases the data rate and improves quality retention through multiple encode/decode cycles, but it is still a 12-bit per channel format. It does not add a 13th bit of log precision. For VFX work requiring the full Alexa 35 sensor data, EXR remains the required format. ### Can DaVinci Resolve handle 13-bit ARRIRAW without data loss? Yes. DaVinci Resolve debayers and processes ARRIRAW in 32-bit float internally. The 13-bit log data is fully preserved within Resolve's floating-point pipeline. The data loss only occurs when rendering to a 12-bit mezzanine format like ProRes 4444. Working entirely within Resolve avoids the problem. ### Is the 13-bit issue relevant for final delivery to Netflix or other streaming platforms? No. Delivery formats for streaming platforms are typically 10-bit or 12-bit. The 13-bit issue concerns the VFX and mezzanine pipeline, not the final delivery format. The problem is managing the data between acquisition and final color, not the delivery itself. ### Does ARRICORE have the same 13-bit problem? ARRICORE is an RGB codec, not a raw Bayer format. ARRI describes it as 18-bit linear ALEV4 sensor data stored in a 13-bit RGB logarithmic file called Sensor Log, with flexible post adjustments for exposure index, white balance, and tint. It does not use the same ARRIRAW-to-ProRes mezzanine decision, but it is currently tied to Alexa 35 Xtreme hardware. ### How does Cutsio handle the 13-bit ARRIRAW review stream? Cutsio generates the review stream from the native ARRIRAW files using the correct color transform. The review stream is a viewing proxy, not a VFX master. The original 13-bit ARRIRAW files remain attached for download, so the VFX house or colorist always has access to the full-resolution source for EXR generation or grading.

13-bit ARRIRAW. Full sensor data preserved.

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