How the ARRI Alexa plays with color saturation to pursue a film aesthetic

How the ARRI Alexa plays with color saturation to pursue a film aesthetic

The ARRI Alexa has been a major player in digital cinema ever since its release and a large part of its success is because of its film-like image quality. As cinematographer Art Adams discovered, that quality may be due to the unique way Alexa handles color saturation and luminance.

What do the ARRI Alexa and watercolors have in common?

That’s a question recently asked by cinematographer Art Adams over at DVinfo.net. While the obvious parallels are true: the Alexa and watercolors both help create images and they’re both tools used in service of art, these aren’t the conclusions Adams looks to draw.

Instead, he offers up a more technical, albeit far more fascinating, comparison about how both the ARRI Alexa and watercolor painting takes advantage of subtractive color. If you are unsure what that means, don’t worry – Adams takes time to explain that subtractive color mediums start with “broad spectrum white palette” and subtract color from it, like watercolor painting on white paper.

Adams further explains the effect this has on color saturation:

“Lighter tones are always the least saturated because that sense of lightness comes from seeing the white of the paper through the paint dyes. Adding broad spectrum white light to any hue will make it appear less colorful. The most saturated watercolors are always the darkest because dense paint blocks most of the spectra from the white base, and removing spectra from white light increases its colorfulness while reducing its apparent brightness.”

This contrasts directly with video and digital cinema cameras which operate using additive color systems. With video, you add more luminance to combinations of red, green, and blue subpixels to create a certain color for a single pixel. This, too, has an effect on saturation, as Adams explains:

“In an additive color system like video the most saturated colors are the brightest. For example, to create the most saturated red possible on a display one simply needs turn the red subpixel up full and turn the others off. A darker red requires reducing the output of the red subpixel, making it appear less saturated.”

So what does all of this have to do with the ARRI Alexa?

Well, it helps to realize that film, through its photochemical processes, is also a subtractive color system. It’s part of what makes film look like film. And Adams cleverly points out through camera tests, experience, and research that Alexa, while operating in an additive color system, is mimicking properties of subtractive color mediums by separating color saturation and luminance after a certain level of exposure in order to adopt a closer film look.

As Adams says, “Video is inherently an additive color medium, and most video cameras embrace that aesthetic. That’s one of the reasons why film and video have such distinctive looks. Alexa seems to buck that trend by emulating the functionality of a subtractive color model in an additive color system.”

To sum it all up, he adds, “I’m not sure it’s fair to say that Arri is ‘emulating’ film so much as they are pursuing a film aesthetic in a digital medium.”

For a deeper understanding into the comparison, I highly suggest you read Art Adams’ post. It includes camera tests shot by Geoff Boyle that illustrate Alexa’s saturation/luminance separation as well as a more comprehensive discussion of the camera and links for further reading.

Read: What Alexa and Watercolors Have in Common

  • John Miguel King

    This is priceless information. However, and I’m quite probably a billion miles off the mark, if I have Log or Raw material off whichever camera I’m using, and said camera has a decent and faithful colour reproduction and such, then all I need to move in the same direction as Arri is a cunningly designed 3d Input LUT in my pipeline to achieve the same results. No?