Working with ARRIRAW
Preparing the Grade
To maintain maximum flexibility and keep the storage requirements down, the camera footage should be kept in the ARRIRAW format as long as possible. Once the deliverables for dailies, editorial and visual effects were created, the original .ARI files can be archived to LTO tapes and sent to the post house. Following a final check that the data on the LTO tapes is OK and that the temporary backup can be cleared, the tapes go into storage.
When it is time to put everything together for mastering, only the shots that were used in the edit need to be restored from the LTO archive. This typically will also be the time at which the ARRIRAW data is converted into color images, so nobody needs to deal with debayering settings in the mastering session.
To get the most out of ALEXA material, we recommend to process the ARRIRAW footage to Log C encoding with ALEXA wide gamut color space.
- Log C is a so-called scene based encoding. The signal level increases by a fixed amount with each increase of exposure measured in stops. Processing ARRIRAW data to images with Log C encoding in the ALEXA-specific wide gamut color space provides the camera's full latitude in an unconfined color space.
When viewed directly, Log C images look flat with desaturated colors. To correctly display Log C material on an HD monitor (Rec 709) or in a digital projection (P3), it needs to be tone-mapped and transformed into the target color space. This image conversion can be performed using a 3D Look Up Table (LUT), which can be created using the ARRI LUT Generator.
- Rec 709 is a display-based encoding using the RGB primaries specified in ITU Recommendation BT.709, and can be directly output to standard HDTV displays without any conversion. Rec 709, however, provides somewhat reduced choices in color grading and, due to a more contrasty characteristic, cannot hold as much highlight information as the much flatter Log C curve. Rec 709 therefore is not a recommended encoding for mastering source material in an ARRIRAW production.
- DCI P3 also is a display based encoding. It is primarily used in digital cinema projectors and an increasing number of LCD displays. DCI P3 has a similar tone mapping to ALEXA Rec 709, but a wider color gamut, which is designed to approximate that of print film.