Create your individual style!
Nowadays the daring question “What will my image look like, when all the processing is done?” can be answered in no time. This can either be the default conversion from ARRI’s logarithmic color space to the viewing color space of a display device or in a creative way via the ARRI Look File.
All ARRI cameras record in Log C wide gamut color space. To converts the flat, desaturated image into a pristine, color-rich image our cameras use the so called "Camera Image Core" (CIC). The camera image core transforms Log C into the desired target color space.
The simplest way of such conversion is to HD or UHD color space (Rec. 709 or Rec. 2020 respectively). This is a straight, technical conversion, details (in the highlights and blacks) might be clipped/crushed by doing so:
The work of CIC can be influenced by an ARRI Look File to alter the colors in the desired way. When an individual (live) color grade is requested, CIC and the ARRI Look File are the anchor-point of your color manipulation.
The look file alters colors “in log space”. In doing so, all color information is there to work with. A look can alter the image based on Color Decision List (CDL) values solely, or by using a 3D-LUT.
Let's have an in-depth look at our different look files – depending on the camera you are using:
ALEXA 35 uses version four of the ARRI Look File (ALF4). Starting with SUP 1.2.1 the camera offers two modes to use the ALF4 look file:
In ACM you are using the full ARRI REVEAL color pipeline (from the sensor until the last conversion where ARRI 3D-LUTs are being used for Standard Dynamic Range (SDR) or High Dynamic Range (HDR) conversion to the desired target color space) with your creative touch, where in CCM you must define your own 3D-LUTs to bring your creative grade into an SRD or HDR color space.
Let’s have a look at an ALF4 using ARRI Color Management. In its essence the ALF4 carries Color Decision List values in combination with a 3D-LUT:
In camera or in the ARRI Reference Tool it is possible to change the look file’s intensity from 0 to 100 in 10% steps.
If we add the intensity setting and ACM to the graphic it gets more crowded, but nothing changes as one cannot influence the ACM. What we just simply called “Custom 3D-LUT” is now called Creative Modification Transform (CMT), because in CCM it would be difficult to differentiate the one or the other “3D-LUT”:
When using Custom Color Management not only the CMT is user definable but also the Display Render Transforms to SDR and HDR. We recommend keeping the CMT a LogC4-to-LogC4 based 3D-LUT and going from LogC4 to SDR/HDR via custom DRTs, but this is not a must. When using CCM mode, Intensity is not available.
Please keep in mind: LogC4 images require new LogC4 Display LUTs
In CCM you are not using “full REVEAL” if you will, because custom DRTs are in place. Both Look Files offer the option for on-set live grading through ASC CDL manipulation (Color Decision List).
To better differentiate which mode the ALF4 is using we added a “c” to the file extension for an ALF4 using CCM: *.alf4c, where the file extension for a regular ALF4 with ARRI Color Management stays *.alf4.
Please note: If you are unfamiliar with the creation of 3D-LUTs acting as a “Display Render Transform” or you want to keep it simple, we recommend playing it safe and using the ARRI Color Management.
ARRI Look File 2 (ALF2) is available for ALEXA Mini, AMIRA, ALEXA 65, ALEXA SXT, ALEXA LF, and ALEXA Mini LF.
ALF2 offers broadcast-style "Video Look Parameters" instead of a 3D-LUT if required.
ARRI cameras use the look file to offer the option for on-set live grading through CDL manipulation (ASC Color Decision List).
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's role in a production shooting with ALEXA Mini for example, it plays a central role in the production’s camera department. ALF2 gives the director, cinematographer, and costume department a close idea about the final image:
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 also 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 or as ARRI Look Files for in-camera use. See below.
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