LUTs, Looks And Scene Files

A Viewing LUT is what people are most often talking about when describing LUTs. They’re designed to make a camera’s output look good during shooting. They may be as simple as converting a flat S-Log or Log C feed into a normal-looking Rec. 709 image, while others also will include some aesthetic choices. A Digital Imagining Technician on set often will create a Viewing LUT for the DP to look at. These LUTs are then sent to postproduction to create dailies and to give the colorist a starting point for the final grade. A Viewing LUT is usually a 3D LUT because it gives the most possible adjustment.

The American Society of Cinematographers (ASC) saw that there was a huge variety of LUT formats out there, which created a lot of problems between on-set tools and postproduction. So they came up with a standard they call an ASC Color Decision List (CDL). This is a 3D LUT with a relatively simple format. Most color-grading software applications can load an ASC CDL file, and many on-set tools can work with these files, so the ASC CDL offers the clearest solution for working with LUTs on set and in post.

Okay, so you have a LUT. Now, how is it applied? Usually, a piece of hardware, often called a LUT Box, is used in between the camera and a monitor. A piece of hardware, like the Cine-tal Davio, Blackmagic Design HDLink Pro or Pandora Pluto, is used to process the incoming image and apply the LUT to the output. Software like cineSpace from THX and Light Illusion LightSpace CMS can be used to combine Calibration LUTs and Viewing LUTs, which can be a tricky process. To learn more about this process and about LUTs in general, check out Light Illusion’s website, www.lightillusion.com.

WHAT’S A LOOK?

RED and ARRI both enable recording in a RAW format, with no baked-in color adjustment. ARRI also has a Log C shooting mode, which is a very flat, wide-gamut video output. Both cameras have the ability to load in special files, which I call Looks, that essentially function as LUTs. The difference between a Look and a LUT is that these Look Files only can be used in-camera. RED’s files are made through their RedCine-X software, and ARRI has a Look Generator. With these tools, a Look can be generated and loaded into the camera. The cameras then can apply the adjustments to their outputs for monitoring. Basically, the Look works like a LUT, but is built just for a specific camera and doesn’t require any external hardware. This type of adjustment then travels through metadata of the recorded clips and can be applied very easily through the right post tools. ARRI also allows you to convert their Look Files into actual LUTs for post, which can be done through their online LUT Generator (www.arridigital.com). The Sony F65 camera will be able to do the same thing in the future with ASC CDL files working as the Look. So the difference between a LUT and a Look is subtle, but because the files are camera-specific, there’s a difference.

MY ANSWER

As long as my explanation was here, I gave the “CliffNotes” version to attendees at our event. The ALEXA Studio camera can load a Look File, generated by the ARRI Look Generator or other software, and its output is adjusted accordingly. That output even could be recorded if the job didn’t want to deal with video in the flat Log C mode. The Look File will travel with the metadata of every clip shot on the ALEXA and can be extracted to make a LUT.

The LUT is created with the ARRI LUT Generator, which creates LUTs in many different formats. This LUT can be loaded to create dailies or into a color-grading application for finishing. RED cameras can do a similar thing, with the look built into the metadata of each clip. I then explained that a Scene File was very different, and is something specific to a camera, created in a camera and baked into the video recording.

These types of conversations are happening in production every day now, and I only see them happening more in the future. Our goal at AbelCine is to help our clients navigate these new waters, and I hope this article helps as well.

Andy Shipsides is a N.Y.-based Camera Technology Specialist and Manager of AbelCine’s Training Department. To learn more about AbelCine’s Understanding HD Series, visit training.abelcine.com.

Required Reading

Get a handle on shooting video in RAW— understand the terminology, benefits, and limitations with our Guide to Raw Video Formats