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posted by - Thursday, 15 January 2009

The ARRI ALEXA is designed for versatility both in the field and in post. One of the traditional barriers for Digital Cinema has been the introduction of new post workflows and data handling. With every new camera to market it seems that there is a new codec, a new file system, and a new set of parameters and tools to master. Often these camera systems are released and working in the field before the popular post production tools are in place or made compatible with the new technology. ALEXA is designed to transition into the workflow of the user’s choice with the popular industry tools available today.

There are three main post paths for ALEXA: Shoot to Edit (ProRes), Uncompressed HD and Uncompressed RAW. Each has its virtues and each is well supported today. With ALEXA, each can work with and complement one another, a unique workflow opportunity.

Shoot to Edit

ALEXA supports a Shoot to Edit workflow, which in the language of ARRI means finished video already compiled into a codec that can be loaded directly into an edit system for post. In the case of ALEXA, it stands for ProRes in both 422 and 444 varieties. ProRes is a very efficient, high quality codec; one that many productions use as a mastering format. In compression quality, it is second only to master-level formats such as HDCAM SR. ProRes is a native format for Apple’s Final Cut Pro and can now also be used natively (in its original QuickTime wrapper) on the latest version of Avid Media Composer.

ALEXA records ProRes onto Sony SxS cards, the same compact and reliable media Sony uses for its XDCAM EX cameras. A 32GB SxS Pro card can hold about 20 minutes of ProRes 422 or 15 minutes of ProRes 4444. With the SxS option installed, ALEXA has two SxS slots on the operator side of the camera. They are “hot swappable,” meaning that a recording will continue across one card to another without having to stop the recording, and cards can be continuously mounted and dismounted, so recording can continue indefinitely.

Recording in ProRes, ALEXA is a compact and self-contained camera. The SxS cards can move directly from the camera to an edit system, and post work can begin immediately with no capturing or recompression necessary (hence the “Shoot to Edit” moniker). ProRes recording is higher quality than almost any other field-recording medium, so this is hardly a compromised workflow. There is another option for using the ProRes files, however, as a smaller proxy version of the other two fully uncompressed outputs from the camera.

Uncompressed HD

ALEXA can also output a full HD signal in 422 or 444 color space over single or dual link HD-SDI feeds respectively. This can be sent into various recorders allowing the ALEXA to fit into common mastering formats. Recorders of Uncompressed HD include units from Codex, s.Two, KG and CineDeck. Perhaps the most popular high-end field recording and mastering format for HD video is Sony HDCAM SR tape. When combined with the Sony SRW-1 deck, the ALEXA HD output can easily be recorded to HDCAM SR. ALEXA can even be at home in multi-camera studio environments where the HD-SDI signal will feed directly into a production switcher or be recorded on a SAN or other server system.

Uncompressed RAW

ARRIRAW is ARRI’s proprietary RAW file format, first pioneered by the ARRI D-21. An Uncompressed RAW signal is the direct electrical value feed from the photosites of the camera sensor without any processing or manipulation. Think of it as the “digital negative” from the camera, where all the processing can be left to post and nothing is “baked” into the look of the image that cannot be changed. There are many post systems that can work natively with the ARRIRAW files such as products from Nucoda, Iridas, Baselight and GlueTools. ARRI also offers free ARRIRAW Converter (ARC) software for systems that don’t yet directly use the RAW files. Field recorders that are currently ARRIRAW-certified include products from KG, Codex and s.Two.

There are a few other tricks up ALEXA’s recording sleeve. Applied color matrix look up tables (LUTs) can be used in any of the recording options and captured (in RAW it is a Metadata reference, since the recording is right off the sensor). ProRes and Uncompressed HD are video modes, so they have to record in video resolution. ALEXA records them at the highest possible HD resolution, 1920×1080, but it actually uses a sensor area of 2880×1620, a 1.5x oversampling. Oversampling increases Dynamic Range, lowers image noise, reduces aliasing and improves MTF (functional resolution). When capturing ARRIRAW, 2880×1620 is recorded in full resolution. Using various post software including ARRI’s own free ARC program, what ARRI refers to as a “True 2K” image can be captured via oversampling. Most other Digital Cinema cameras offer either oversampling or a large RAW resolution; ALEXA offers both.

ProRes is a higher quality recording format than most other field portable options. Uncompressed HD allows ALEXA to fit in with a myriad of current workflows and other formats. ARRIRAW is the finest, richest signal available for extracting all of the useable information from the camera. Each option offers a mix of convenience, compatibility and quality. Each is easy to use for the operator and each is fully integrated and functional with today’s post production world.

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