An introduction to the ACES colour space and how it can be applied. ACES is a container colour space that streamlines working with many different cameras and deliverables. The system is an open standard that is developed and maintained by the Academy of Motion Picture Arts and Sciences.

Introduction

ACES is a container colour space that streamlines working with many different cameras and deliverables. The system is an open standard that is developed and maintained by the Academy of Motion Picture Arts and Sciences.

The system is designed to work as an intermediate colour space that encompasses the full CIE 1931 chart and all the gamuts that can be defined within it. By having this container space, the ACES system makes it much easier to work with many different camera formats and colour pipelines. This is particularly useful on shows where there are numerous different cameras that all record into their own log colour space. Its use case extends to VFX work and managing shows with a lot of deliverables. These could be SDR/HDR as well as P3.

The ACES Pipeline

The ACES pipeline is split into several sections. Each section is a process in a series of colour transformations that ultimately render a viewable image in the colour space of your choice on the display of your choice.

The IDT (Input Device Transform)

The IDT is the first step in the ACES pipeline. This is responsible for mapping the source material, ARRI Log-C for example, into ACES Linear (AP0). Depending on the working colour space and project settings an additional colour transformation maybe applied, this transforms the ACES linear to ACEScc or ACEScct.

ACEScc/t are two of the three derivatives of the ACES colour space, the third being ACEScg.

ACEScc: uses a log encoding to make the grading tools feel more familiar to colourists

ACEScct: is the same as the ACEScc derivative, with the addition of a toe to the log encoding. This makes the lift and exposure change operations feel more natural and allows these operations to respond in a familiar way.
ACEScg: The cg element in this derivative stands for computer graphics and is a linear encoded ACES space that allows for greater interoperability in ACES VFX/CGI workflows.

The LMT (Look Modification Transform)

The LMT is the next step in an ACES pipeline. This is the step in which a constant creative change to the image can be applied, this step is similar to the use of creative LUT’s in a legacy workflow and can be distributed as a 3D cube.

The 3D cube that describes an LMT does not contain any gamma mapping, just the creative grade. If an LMT is applied to a log image outside an ACES environment, the image would only change slightly and would still be in its log colour space.

In order to ensure that the image retains its maximum scope for creative grading, the LMT is applied after any changes made by a colourist, similar to how traditional non-aces LUT’s would be applied.

The RRT/ODT (Reference Rendering Transform & Output Device Transform)

This is the final step in the ACES pipeline. The RRT is defined as the render engine that works behind the scenes before the ODT to help create viewable images.

The ODT is a user selectable configuration which can be switched out on the fly to view the image in the display format that is most appropriate to the viewing / mastering environment that you require. This could be Rec709 SDR or P3.

Conclusion

This is a brief intro to the ACES pipeline that should be enough to get anyone started or provide a stepping stone to further study. I plan to add some more articles and case studies on ACES in the future.

Personally, I think that ACES is a great standard that simplifies working with lots of different cameras on a project. By using ACES, one LMT can be applied to any source, which makes adding different formats to a project much simpler.

There are a few caveats to the ACES pipeline, the biggest being that IDT’s must be made available by the camera manufacturer. This isn’t a huge problem as most established cameras have an IDT. However, additional steps need to be made when working with prosumer style cameras such as the DJI drones.

An Introduction to ACES and it’s application.