ACES WORK FLOW
Cortex supports the optional use of the Academy Color Encoding System (ACES), for consistent control of color throughout the production work flow. In addition to operating in a specific working color space, an ACES work flow also requires the ability to maintain a desired dynamic range throughout. To allow for this, output is typically done via OpenEXR, an image transport format that handles a very high dynamic range.
The ACES Input Transform is an image processing step that converts native images from selected cameras into the ACES color space (SMPTE 2065-1). Camera types currently supported include Arri Alexa, Sony RAW, Red, Canon, Panasonic Varicam, as well as DPX files encoded as Academy Printing Density (ADX).
ACES Working Space
In addition to working in the normal ACES 2065-1 color space, Cortex can also operate in ACEScc (a logarithmic encoding generally used for color grading), ACEScg (generally used for CGI work), or ACESproxy (an integer space that can be used for SDI output).
Color Correction / Look Modification Transforms
Primary color correction is applied in whichever ACES working space has been selected. Additionally, creative Look Modification Transforms can be applied. These are supported in Cortex via the AMPAS Common Lut Format (CFL) LUTs.
This step consists of two parts, a Reference Render Transform that converts the ACES working space image into an idealized colorimetry with no dynamic range or gamut limitations, followed by an Output Device Transform, which then converts the image for the desired display device, such as rec-709, rec-2020, P3, etc.
CORTEX CONFIGURATION FOR ACES
When creating a new Cortex project or editing an existing one, selecting an ACES version will enable additional options in the Cortex Color Tool and in the project Deliverable Configuration editor. Cortex currently supports ACES version 1.0.
The deliverable configuration is used to set the ACES working space, and the final ACES Output Transform for a given deliverable, or for the Cortex Preview configuration, in much the same way that it's used to set a display LUT for non-ACES work flows.
If the current project has ACES enabled, the deliverable configuration tool has an additional tab labeled 'ACES'. This tab contains a selector to set the ACES working space, the Reference Render Transform, and the Output Device Transform.
A typical setup for many Cortex users would be a combination of the normal ACES2065-1 working space, ACES 1.0 RRT, and ACES 1.0 Output – Rec.709.
When the current project has ACES enabled, the color tool contains a new tab labeled 'ACES Input' for selecting the Input Device Transform for each video source clip.
For some cameras, notably Arri, there are a large number of possible input transforms, each for a specific camera exposure index and color temperature. Checking the 'Filter by camera metadata' check box in the ACES input tab will limit the choices those transforms that match the values found in the metadata of the current clip.
Note that when working in an ACES work flow, many of the usual creative controls for some camera formats, notably the RED camera, are no longer usable. This is necessary to maintain consistent color through the post production process.
I/O CONSIDERATIONS FOR ACES WORK FLOW
Any deliverables intended to contain the ACES2065-1 space should be done as openEXR to maintain the high dynamic range. When configuring an openEXR configuration for ACES, select the 'ACES container (SMPTE 2065-4)' compression method.
APD DPX deliverables
The Academy Printing Density Exchange (ADX) DPX format provides for encoding either 10-bit or 16-bit DPX files with RGB printing density encoding. This format can be selected in Cortex when creating a DPX deliverable configuration.
ACESproxy is an integer log encoding of ACES image data that can be transmitted via 10-bit SDI, typically for on-set preview and on-set look management applications.
For those Cortex installations that are using SDI output, the SDI signal can be configured to use ACESproxy encoding in the Cortex hardware user control.