Turning to how colors are handled, Demos and Walker detailed a number of very complicated issues with color rendering (you should read the paper to fully understand all the issues). The shape also makes it invertible to transform forward or backward over a very wide range. 18% gray in the scene is mapped to 10% of the SDR white point (i.e., 4.8 cd/m² for cinema, 10 cd/m² for television), which is the customary placement for cinema and dramatic television.ĭemos said they spent a lot of time looking at the shape of the curve, especially the highlights and low lights to get something that performed well, which is why they settled on the linear slope regions as indicated. He says this follows the ACES 1.0 curve in the mid-tones, but deviates in the bright and dark tones. The new HDR single-master tone curve (Nugget) that Demos and Walker propose is shown in the graph below along with the ACES 1.0 RRT and RRT/ODT combinations. In particular, problems with clipping as well as hue and saturation shifts were evident with ACES 1.0. The ACES master is now considered the point after aesthetic rendering preambles are applied.Īt a companion demo session we attended at the home of Joe Kane, Demos showed a number of color charts and other HDR images where he pointed out the problems with the ACES 1.0 rendering and how his algorithms can fix these issues. They believe this approach is more flexible and preserves chromaticity from start to finish. The current ACES workflow and the proposed new modules are shown in the graphic below. The idea that Demos and Walker are proposing is to split up the RRT into separate color (aesthetic rendering preambles) and gray scale modules (Nugget tone curve) and split up the ODT into two parts that allows for device specific adjustments to color and luminance (display formatting) but also have separate modules they call parametric appearance compensation, which adjusts colors and luminance based upon the viewing environment.
Unfortunately, the RRT is not reversible, so you can’t get back to the ACES master data very easily and alternative RRTs are not allowed, so it becomes very difficult to fix any final errors. These errors then get passed on to the ODT and become visible on certain scenes. Output Transforms have some hue and saturation distortionĪccording to Demos, the RRT, which manipulates color and gray scale simultaneously, desaturates dark and bright tones while boosting saturation in the mid tones.Clamping outside the rendering primaries.The problems that Demos and Walker are trying to solve were identified as: These transforms are designed to be done in real time on available hardware. These transforms massage the color volume and gray scale accounting for the capabilities of the target display and the viewing environment.
The user then selects one of a number of Output Device Transforms (ODTs) that are tailored for specific display platforms such as a cinema projector or grading monitor. To display content, it is first rendered using the Reference Rendering Transform (RRT) which applies a mandatory transform to a specific color space and grayscale range as a first step. The finished work is referred to as the ACES master. Having all the assets in a common ACES format makes it much easier to match up white points and colors from various cameras or other assets to create a uniform look. In the ACES format, which is based on RGB, common editing, effects and color grading tools can be used to finish the content.
#Cinema grade aces full
ACES 1.0 adds a full workflow for the conversion of source materials into the common ACES format via a series of input device transforms (IDTs) tailored for each source format. The idea is to transform all of your assets into one common linear light file format which was large enough to contain a very wide range of luminance and color values. Dozens of formats existed, making conversions difficult and archiving nearly impossible. All About ACESĪCES was started as a file format project to create a common format for all the assets used in production and post production. Matt Brennesholtz also gave a good summary of the features in November 2016, which I paraphrase next.
#Cinema grade aces update
However, to understand why Demos and Walker think an update is needed, we need a little background on ACES 1.0, which was formally released at NAB 2015 after 10 years of development (see video). Gary Demos of Image Essence and Doug Walker from Autodesk Media & Entertainment gave a very good presentation on a new color management solution that they believe should be considered for the next version of ACES, the color management solution release by the Academy of Motion Picture Art and Sciences.
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