ACES Workflow

This tutorial provides information on how to configure Color Management to work with the OpenColorIO implementation of the Academy Color Encoding System (ACES), as well as a summary of what ACES is. The article is divided into two parts, theoretical and practical. The theoretical part will help you understand some of the basics of ACES, and how it works, before you get down to the practical part, and consider some of the nuances in setting up Color Management.

What is ACES and Why is it Recommended?

The Academy Color Encoding System (ACES) - is a free, expandable, device-independent color management and image sharing system developed under the auspices of the Academy of Motion Picture Arts and Sciences. It is also a set of technical specifications for working with color, coding, and transformation. This system allows you to store all the data of digital images in the same mathematical space, which allows a more consistent workflow during the transfer of working material between different departments. It is also important that ACES allows you to create archival materials with a high dynamic range and wide color gamut, even taking into account possible future devices.

ACES 1.1 (current release). Some of its features include:

• Wide range of color and light, exposure.

• Predictable image display on a wide range of display devices.

• Preserving the full range of highlight, shadows, and colors.

• Simplifying the matching of images from different cameras.

• More accurate color display with no incorrect color values.

• Work in Linear color space.

• No over highlight and clamp, on bright areas of the image.

• And more...

ACES Workflow

ACES consists of several components:

• Input Device Transform (IDT) - Color conversion from input material. More properly called an Input Transform.

• Reference Rendering Transform (RRT) - Color transformation from scene-referred to display-referred space, using an S-shaped tone curve, image preparation for output.

• Output Device Transform (ODT) - Transforms to an output device, a transformation such as Rec. 709, DCI-P3, Rec.2020.

In practise, the RRT and ODT are combined and called an Output Transform.

ACES Color Spaces

 

ACES contains different color spaces, we will look at the main ones:

• ACES 2065- 1 - This is a wide-range Linear, color space, with a larger coverage than the human eye, so it is used for archival copies and transfer of material between departments.
• ACEScc and ACEScct - Logarithmic color spaces intended for color correction.

• ACEScg - This is a Linear space for working with CG/VFX. This is the space you need to use as the main color space for working with color set-up and light in your rendered images. More information is available here.

Workflow

Download

• First, you will need to download the OpenColorIO (OCIO) configuration package for core ACES transforms https://github.com/imageworks/OpenColorIO-Configs/tree/master/

Set OCIO Config Path

This can be done in two ways:

• Next, you will need to add the path to the downloaded ACES configuration in Maya (most 3D graphics packages already contain a predefined configuration package), but in this case, we will use the downloaded version.

• Install the OCIO variable with the path to the config.ocio file. This can vary according to your ОS (you can install OCIO as the default color configuration for all apps). This can be in the Maya.env or in the user Preferences (similar to the OS variable but only for Maya). For example: 

OCIO = C:\OCIO\aces_1.0.3\config.ocio

• Or you can set the path to the config.ocio file in the Maya Preferences for working with projects.

 

We will consider the second option:

• Start Maya and create a New Project. Open the Preferences window (Windows-> Settings/Preferences-> Preferences). Go to the Color Management settings.

Color Management Preferences

• Set the path to config.ocio at OCIO Config Path

• Enable Use OCIO Configuration

Set Transform Preferences

• Rendering Space ACES - ACEScg.

• View Transform Rec.709, D60 sim. (ACES).

Define Color Space Rules

Go to the Input Color Space Rules, and choose OCIO Standard Rule or Default. When using Default, you can change the color space by default to what you need, when opening all images in your scene. For example, choose ACES-ACEScg in Rule Conditions -> Add Image Color Space (for opening images), and save your Preferences and scene. 

Alternatively, you can deselect 'Use OCIO Input Color Space Rules' so that you can add your own rules for various file formats.

 

The main color spaces for conversion will be:

• Utility-Linear - Rec.709 or sRGB - choose this for Linear images that use the Rec.709 or sRGB primaries/gamut (which are the same).

• Utility-RAW - for images that do not require conversion (scalar masks, Displacement, Roughness).

• Utility-Rec.709-Camera - for sRGB images, 8-16 bit (lightmaps, matte paints), (JPEG, PNG).

• Utility-sRGB - Texture - recommended color space for sRGB image textures 8-16 bit (JPEG, PNG).

ACEScg - Color space for images that are already converted to ACEScg.

For all other images, not converted to ACEScg, you will need to individually set-up the color space for the aiImage and File nodes.

 

Remember, if you create a project with ACEScg as the rendering space, you will need to set the Maya Color Space so that all images get correctly converted to ACEScg. Images in other color spaces will look wrong without conversion.

 

 

^{Thanks to Doug Walker and Slava Sych for their assistance with this tutorial.}