7.0 What is ACES and why did I use it
What Is It?
ACES is the Academy Color Encoding System, developed to future-proof everything in the motion picture industry and achieve a more uniform way of encoding color for movies. It is a high-precision encoding system designed for mastering, interchange, and archival purposes. As an industry standard, it is used for high-end productions, facilitating easier collaboration between different post-production houses by ensuring everyone encodes images in the same way. This results in a more uniform picture and reduces color compression. Without ACES, there would be more issues and variables, making it difficult to blend content together.
ACES is a scene-referred, appearance-correlated colorimetry system. It has evolved from the Cineon encoding space, which uses reference-printing density and encodes it as Academy Density Exchange (ADX). In contrast, video systems optimize color for small gamut displays and employ device-dependent RGB encoding. Dynamic range is restricted to the display and typically uses 8-bit encoding formats. In these systems, the display plays the largest role, requiring proper calibration to ensure accurate colors. However, these earlier workflows are easier to use.
The ACES workflow manages the differences between various cameras used on set, helping them match. Images are digitally encoded and converted using an Input Device Transform (IDT), which converts imagery from their color space into the ACES color space. During post-production, these images need to be viewed, particularly for visual effects work, which is done using a Reference Render Transform (RRT). The RRT converts ACES into the ideal color space for rendering on-screen. Finally, an Output Device Transform (ODT) is used for conversion, as not all monitors have the same gamut. One of the many benefits of ACES is that there is no compression! This is possible because the ACES color space was made larger than the full visible gamut, and this can be done because it is simply just math.
Why Is This Important For VFX Work?
As a behind-the-scene type of person; if the job is done right, no one will notice you.
In the visual effects industry, the goal is often to create work that seamlessly blends with live-action footage. If done right, nobody will notice the VFX work. ACES is a tool that can help cover the subtleties within a shot and make it easier to match created 3D work with captured live action. There are numerous factors that influence the believability of a shot, and having a robust color encoding system like ACES can greatly contribute to the overall result.
Working in a color space that allows for the use of every visible color makes it easier to match visual effects work with live-action plates shot on any camera. Imagine trying to composite a photo taken with your phone with a compressed image from the internet. Despite your best efforts to match the two photos, the final result might still look 'Photoshopped.' However, if you took that photo from your phone and composited it with one taken using a DSLR shooting in raw format, the compositing process would be much easier and more seamless.
There are many factors that contribute to a well-composited shot, but when it comes to color, having access to as many colors as possible is invaluable. The best analogy is to think about is a box of crayons. Everyone got the standard 16-pack, or 32-pack. But if you were the kid with the 64 or 128-pack of crayons, the possibilities you could create were endless!
ACES ensures the best color reproduction and color management for a project. Any compression could ruin the shot and make it look off, so using a system like ACES can greatly improve the final outcome of visual effects work.
The Process
To ensure that the footage is not compressed and is encoded properly, the raw footage must go through some processing, following the ACES workflow. Once processed by the DIT (digital image technician), the footage can be imported into Nuke as DPX files or .ARI files.
In Nuke, ACES must be set up. After ‘reading’ in the footage, it should be placed into a linear color space by setting the color space dropdown to 'linear'. In the project settings, under the OCIO config tab, select 'ACES' as the OCIO (Open Color Input Output). A lookup table (LUT) can be used if desired, but matching color is typically easier in a linear color space. In the display window, change the viewerProcess to 'RRT(sRGB)'. The RRT (Reference Render Transform) allows the linear format to display correctly on any monitor used. (See video below.)
This project was completed in 2016 - the process is a bit out of date.
Color correcting each element to match the background plate is essential. Once each piece closely matches in color, an overall grade can be applied to the images. When writing the footage out, ensure that the desired color space is set on the write node.
If the footage is to be color graded in another software, a linear color space should be chosen. If the final render and all color correction is done within Nuke, a color space like sRGB or Rec709 would be appropriate.
Notes:
Some of the process is a little outdated at this was made in 2016. Some things have changed
