Look Files

What you see is what you get, but with the freedom of Log C

In digital production one question is always present: “What will my image look like, when all the processing is done? Is it really what-you-see-is-what-you-get?” Yes, kind of! As described in our Log C section, all ARRI cameras record in Log C wide gamut color space. The camera image core (CIC) utilizes a look file to transform the flat, desaturated image into a pristine, color-rich image, followed by a color space transform either in-camera (ALEXA 35) or as part of the look file (all other ALEXA/AMIRA cameras).

This can happen in various ways. The most simple is using a conversion into HD or UHD color space (Rec 709 or Rec 2020 respectively). This is a straight, technical conversion. Some details in the highlights and blacks might be clipped by doing so:

When more advanced color grading or an individual live color grade is requested, the CIC and an ARRI Look File can be the anchor-point of color manipulation. The look file always alters colors “in log space” so as to have all color information to work with. A look can alter based on Color Decision List (CDL) values solely, or in addition to a full 3D LUT.

wkflw_Lookfile_basic_logc-and-look-to-709

ARRI Look File 2 (ALF2)

ARRI Look File 2 is available for ALEXA Mini, AMIRA, ALEXA 65, ALEXA SXT, ALEXA LF, and ALEXA Mini LF.

ALF2 also offers Video Look Parameters instead of a 3D LUT if required.

ARRI Look File 4 (ALF4)

ARRI Look File 4 is only available in ALEXA 35 and requires log-to-log LUTs, where the color space conversion is being handled in-camera in CIC, or later in postproduction (again in CIC).

In both formats CDL offers the option for live grading.

Like other metadata, for example camera status information or lens metadata, the look file travels in each clip’s file header. This means if you have the original file, or a copy of it, you can extract the look file. Transcoding destroys all the embedded metadata. Looking at ALF2 in, for example, ALEXA Mini, it plays a central role in a production’s camera department. ALF2 gives the director, cinematographer, and costume department a close idea about the final image:

ALEXA 35, on the other hand, offers more flexibility, because we’ve added the option to do the color space transform in-camera, so it is possible to output to different targets:

ARRI Look Library

The ARRI Look Library is a collection of 87 looks that are available pre-installed in-camera. Due to their variety, the looks cater to a lot of different shooting scenarios.

The looks are numbered within nine themed groups: Application, Black-and-White, Contrast, Environment, Film, Period, Season, Special, and Tinted. In a sense, the looks can be thought of as being similar to different film stocks, each providing a unique but repeatable aesthetic when combined with the cinematographer’s choice of lenses.

The Look Library is a tool for on set as well as for postproduction: a look can be a grading node in a more complex setup or work on its own. When a look is selected on set it travels as metadata in the clip's file header into postproduction, where it can be extracted and exported as a 3D LUT. To ease the use in postproduction and the development of custom log-to-log look variants, we're offering log-to-log versions of the Look Library free of charge. In general there are two Look Libraries: "LogC3" and "LogC4" - choose the right one depending on which camera was used on your project:

The looks are available as *.cube log-to-log 3D LUTs which can be converted into ALF2 or ALF4 Look Files again using the ARRI Reference Tool or ARRI Color Tool (ALF2 only).