The ACES Color Space: The Gamut to End All Gamuts

on February 01 2012 10:47 PM

A development in the field of color science called ACES will let video professionals work with footage less destructively at the post-production end of the pipeline. This has immediate ramifications for shooters, colorists and visual effects houses and will be accomplished by utilizing a much wider gamut than the current specification for high-definition video.

First, some context. What the heck is a gamut anyway? 

A gamut is simply the range of colors that a device can display. Displays are based on a three-color primary system of red, green and blue. In the image that accompanies this article you'll see a chromaticity diagram, a visual blob that represents the entire range of colors that the human eye can see.

It gets its shape from the numbers running along the sides, which correspond to that color's wavelength. The triangle inside this blob represents the result of our three-color system. The colors inside that triangle can be displayed by a device using that specification, in this case the HD video standard. (D65 is a fancy way of saying, here's where white is.)

As one can plainly see, there are a lot of colors the display cannot see, green for example, but a lot of those values are pretty similar once you get near the edges of the graph. Still, video professionals will want the ability to show the full range of color data as footage acquisition becomes more sophisticated each year. The push toward affordable 4k displays will demand the utmost pristine picture quality.

I sat in on a lecture given by Michael Chenery, the senior color scientist at THX.  Chenery's lecture was informative enough to give you a nosebleed; there's no doubt the guy knows his stuff, and you could easily listen to the lecture several times and glean new information from it each time.

In the lecture he explained that one such answer to limited gamuts is the ACES (Academy Color Encoding Specification) color space, which uses imaginary primary colors to include the entire range of colors shown in the diagram. Imagine a triangular lasso that ensnares all of the values on the blob. To do that the colors that define the three-color triangle would have to be outside the colors humans can see; the colors are imaginary in that sense, but mathematically able to be utilized.

Imaginary colors may sound like science fiction, but this is only the tip of the iceberg for ACES. Monitors that can display this color space are slowly being utilized in post-production, as artists can switch their systems to work in the higher resolution format of ACES, and then convert back to HD so that it can be shown as intended.

ACES will eventually replace the standard for HD as displays go beyond the size of native 1080p resolution, as even this year's Consumer Electronics Show saw growing desire for 4k monitors.

Tristan Kneschke is a freelance editor and colorist who operates Exit Editorial.

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