Welcome to the world of ACES

The Academy Color Encoding System (ACES) is a global standard for managing color in motion picture, television, video game, and immersive media production. It provides a consistent and reliable color experience from image capture through editing, visual effects, mastering, presentation, archiving, and future remastering. ACES ensures that the creative vision is preserved across all stages and formats.

Background
ACES was developed for over twelve years by the Academy of Motion Picture Arts and Sciences’ Science and Technology Council, with contributions from camera manufacturers like ARRI, Sony, and Canon, as well as film companies such as Kodak and FUJIFILM. The system supports both digital and photochemical workflows and is built on open standards including OpenEXR and DPX. Its collaborative foundation makes it a trusted solution across the industry.

Key Concepts
ACES introduces the concept of image state, which defines whether an image is intended to represent the original scene or its final display version. Scene colorimetry refers to the actual light and color captured by a camera, while display colorimetry describes how that scene is reproduced on a screen.
To convert scene-referred images into display-referred ones, ACES uses a rendering transform. This process includes the Reference Rendering Transform (RRT), which adds film-like characteristics, and the Output Display Transform (ODT), which adapts the image for specific devices such as projectors or monitors. ACES files are stored in standardized formats.
The ACES Container uses OpenEXR to hold colorimetric image data, while ADX is a constrained form of DPX used for densitometric film scan data. These formats ensure compatibility and accuracy throughout the workflow.

Strengths
ACES is built on a strong theoretical foundation, supported by years of expertise from camera, film, and display manufacturers. It is vendor-neutral, meaning it works equally well across different camera systems. The system is thoroughly documented, with multiple SMPTE standards and Academy white papers available. Most importantly, ACES simplifies the process of matching images from different sources, making it an essential tool for professionals seeking consistent and high-quality results.

Workflow
ACES does not mandate a particular workflow, but there is a fairly common ACES-based workflow that is flexible enough to meet most production needs. In this workflow, there are four points at which the color values in the captured scene can be changed for creative or for technical reasons:

• in a show look
• in an on-set grade
• in a VFX pre-grade
• and in the final DI grade

If the workflow sounds familiar, it is because this type of workflow was established for high-end VFX-heavy productions long before ACES was developed.

ACES supports 10-bit and 12-bit proxy formats for on-set use, known as ACESproxy10 and ACESproxy12. These are simplified encodings designed for monitoring and grading, not full-resolution ACES images. ARRI cameras do not output ACESproxy signals directly, but monitoring in ACESproxy is possible using external hardware that converts Log C signals and applies ACES transforms. This can be achieved through live grading systems, smart monitors, or 3D LUT boxes.

Advanced live grading tools can convert Log C signals to ACESproxy, apply ASC CDL grading, and render the final image using ACES transforms. These systems can also use ACEScc, a full-precision floating-point encoding, to achieve identical grading results across luminance ranges.

Colorspaces – ACES Encodings: ACES2065-1, ACEScg, and ACEScct
The Academy Color Encoding System defines several color encodings tailored for different stages of the production pipeline. The three commonly used are ACES2065-1, ACEScg, and ACEScct—each serving a distinct purpose while remaining interoperable within the ACES framework.

ACES2065-1
This is the reference color space of ACES, designed for archival, and ensures lossless as well as consistent data transfer. It uses a linear encoding and extremely wide color primaries (AP0), encompassing all visible colors. It is not intended for creative color grading.

ACEScg
ACEScg is a linear color space with slightly narrower primaries (AP1), optimized for computer graphics and visual effects.

ACEScct
Designed specifically for smooth tonal adjustments in color grading, ACEScct uses a logarithmic encoding. It mimics traditional log curves like ARRI Log C, making it intuitive for colorists. 

ACEScct operates within the AP1 color primaries, a set of RGB primaries that offer a wide but manageable gamut. AP1 was chosen for ACEScct to avoid the numerical instability that can occur when grading in extremely wide-gamut spaces like AP0. Its design ensures compatibility with grading tools and provides a more predictable and artist-friendly behavior across luminance ranges.

How They Work Together
In a typical ACES workflow, image data is first converted into ACES2065-1 to establish a standardized baseline. For creative tasks like grading or VFX, the data is then transformed into ACEScct or ACEScg, respectively. After processing, the images are converted back to ACES2065-1 for final output and archiving, followed by an Output Display Transform (ODT) tailored to the target display device. On-Set workflows may derive from that.

The modular approach enables a clear separation between technical and creative processes, while maintaining color consistency and preserving artistic intent throughout the entire production pipeline.

On-set Grading
On-set production optionally produces a set grade. If it does produce such a grade, then the grading parameters, expressed as an ASC CDL file, are passed from set to near-set or editorial, and thence to VFX, and finally (as a starting point or hint) to the final grade.

VFX
Modern VFX tools support ACES workflows through OpenColorIO (OCIO), an open-source color management system. With ACES-compliant OCIO configurations (version 1.0.1 or later), these tools can handle ACES color spaces and transforms reliably.

Final Grading
In the final stage of postproduction, ACES images are color graded using specialized tools that support ACES container files or direct camera formats with appropriate transforms.
Because ACES images are linear and human vision responds logarithmically, final grading is performed in ACEScc, a logarithmic color space. This ensures that any ASC CDL grades applied on-set to ACESproxy data will behave identically when applied in the DI session to ACEScc data.

While on-set grading metadata continues to accompany the image, it serves more as a reference than a directive. The purpose of final DI grading is to refine and enhance the creative look of the production. As a result, the visual consistency maintained between on-set, editorial, and VFX may evolve during this final stage to better serve the artistic goals of the project.