Digital capture

ARRI digital cameras do not directly produce or record ACES imagery. Instead, they produce either ARRIRAW data, QuickTime-packaged ProRes clips or MXF-packaged DNxHD clips. The data or clips can be converted to OpenEXR files full of ACES image data and metadata, fully conforming with the ACES image container standard (SMPTE ST 2065-4:2013, ACES Image Container File Layout). Note that only ProRes or DNxHD clips recorded with a Log C "REC processing" can be converted to ACES.

As the frames are not being recorded as native OpenEXR frames, but instead are being recorded as ARRIRAW data or ProRes or DNxHD clips, all the image-format-specific information regarding frame rate ranges, resolution, frame size, data volume, etc. that is found in non-ACES sections of these Workflow pages is equally appropriate for ACES production.


Signal monitoring

ACES defines 10- and 12-bit encodings, used on-set only, to pass gradable imagery around the set. These are not 16-bit float encodings of the ACES image, but are lower-bit-depth "proxy" images, termed "ACESproxy" images. The 10-bit on-set encoding is called ACESproxy10; the 12-bit encoding is called ACESproxy12.

Current ARRI cameras do not have a way of directly producing an ACESproxy monitoring signal, but it is still possible to monitor in ACESproxy with the appropriate downstream hardware using an external device that can convert Log C to ACESproxy and apply the ACES transforms appropriate for an on-set display. Mechanisms to do this type of monitoring (possibly including grading of ACESproxy data with ASC CDL) include: 

  • Using a node-based on-set live color grading system that is powerful enough to allow concatenation of multiple 3D LUT and ASC CDL operators
  • Using a monitor with with 3D LUT support in conjunction with an ACES-savvy application that performs ASC CDL grading
  • Using an external 3D LUT box in conjunction with a monitor that accepts ACESproxy input and that internally performs ASC CDL grading
  • Using an external 3D LUT box in conjunction with a standard monitor (foregoing any ASC CDL grading of the ACESproxy signal)

Grading with on-set live color grading systems
Highly configurable on-set live grading systems such as OSD Live! from Colorfront or Daylight from Filmlight can be set up to take a live Log C input signal, convert it to an ACESproxy signal, optionally apply ASC CDL grading operations to that signal, convert that (possibly modified) ACESproxy signal back to an ACES signal and finally apply the ACES output transform. Diagramatically this is shown in the figure below:

Note that the diagram shows the ASC CDL application to ACESproxy10 data. If the software package (here Colorfront OSD Live!) chooses to do so, it can convert Log C to the logarithmic full-precision floating-point encoding of ACES, termed ACEScc, in place of ACESproxy10. ACESproxy (both 10- and 12-bit versions) and ACEScc are designed so that, in terms of the results obtained, ASC CDL grades of ACESproxy and ACEScc will produce identical results across the luminance ranges one encounters on-set.

Grading with "smart monitors" and supporting apps
Some recent monitors, like the Flanders Scientific DM250, have enough internal processing power so that in conjunction with a grading application like Pomfort's LiveGrade Pro, the monitor can itself convert the Log C signal to ACESproxy10, apply ASC CDL, apply the ACES viewing transform and then display the result. This is shown below:

For information on this approach, see the Pomfort LiveGrade Pro support page explaining the use of this workflow. The Pomfort Livegrade ACES CDL panel is shown below.

Grading with 3D LUT boxes and "smart monitors"
Other monitors, though they cannot provide internal Log C to ACESproxy10 conversion, are capable of using ASC CDL to manipulate that data, and then applying the ACES viewing transform. When these monitors are fed a signal that has been converted upstream from Log C to ACESproxy10, they can be used with ARRI cameras in an ACES-based on-set workflow.

In the illustration below, a Fujifilm IS-mini 3D LUT box is using a Log C-to-ACESproxy10 3D LUT to perform such an upstream conversion. The Canon DP-V3010 provides a display controller with knobs that can adjust ASC CDL values applied to the incoming ACESproxy10 signal, and then render the result with the ACES viewing transform. ASC CDL values are exportable on a USB stick from the monitor's display controller.

Users of such outboard 3D LUT boxes should be aware that the conversion between Log C and ACESproxy10 is exposure-index specific, and that to maintain a strictly accurate conversion from Log C to ACESproxy10, the appropriate EI-specific 3D LUT should be loaded each time the ALEXA or AMIRA's exposure index is changed. That said, if a Log C to ACESproxy10 3D LUT for a mid-range exposure index such as EI 800 were used, the differences from nominal Log C to ACESproxy10 conversion would almost certainly not be visible in the context of a working set.

For the particular case of the Canon DP-V3010, users should verify that the display’s firmware is up-to-date, as the ACESproxy encoding changed between the time the display was first shipped and when ACES 1.0 was finalized in December of 2014.

Monitoring with 3D LUT boxes
If on-set monitoring is all that is required, the same on-set 3D LUT box used above could be loaded with a Log C to Rec. 709 3D LUT that performs, as one concatenated set of conversions, a Log C to ACES conversion and an ACES viewing transform for a Rec. 709 device. Such a setup is shown below.