Welcome to ARRI's Color FAQ section. Discover essential insights into color management within camera systems, tailored for cinematographers and filmmakers.
Here, we address common questions about ARRI’s color science to help you enhance your footage and achieve stunning visual results. Explore our expert guidance and take your projects to the next level.
The ARRI Look File 2 (ALF2) is our 2nd generation look file used in ALEXA SXT, Mini, AMIRA, ALEXA LF and ALEXA Mini LF. The ALF2 supports ASC CDL as well as the use of a 3D-LUT for custom color transformation to Rec. 709, 2020 or P3 color spaces. Use the ARRI Color Tool (legacy) or 3rd party software to create an ALF2 look file.
The ARRI Look File 1 (ALF1) is our discontinued Look File an was replaced by the ALF2 (ALEXA SXT, Mini, AMIRA, Mini LF) and ALF4 (ALEXA 35 and later).
The ALF1 can not deal with any 3D-LUTs and only use printer lights, saturation and CDL values.
Use ARRI Look Creator (ALC) to create ARRI’s Look File 1 (ALF1) to use in ALEXA Classic and XT. Based on a *.dpx still frame you can create look by using printer lights, saturation and CDL values.
ALC is a free application for Mac and Windows computers.
Please note: The ARRI Look Creator (ALC) and the ARRI Look File 1 (ALF1) is end-of-life (EOL) and has been discontinued. Nevertheless there are still possibilities generating looks for your ALEXA Classic and XT. Please have a look here...
Conversion of ALF-1 looks is easily possible with our ARRI Color Tool. Open your ALF-1 (*.xml) look file and export it as an ALF-2 look file (File > Save Look as).
Here's a step-by-step guide for using ARRI Color Management:
First you need a 3D-LUT. This must be a Logc4-to-LogC4 LUT as a *.cube file with 33 or 65 mesh points.
The Look Library "for post production" is available as Log-to-Log 3D-LUTs (*.cube) for LogC3 and LogC4 on our Look Files Website.
Some 3rd party applications are able to read the ALF-2 information directly out of the ProRes clip or ARRIRAW file header (e.g. Blackmagic Design’s “DaVinci Resolve Studio”).
An ALF1 can still be created by our ARRI Look Creator (ALC), but the software is EOL and is not maintained since OSX 10.8.
There are 3rd party possibilities to create ALF1 files with:
Pomfort Livegrade Pro
The ALF1 functionality was removed from the Livegrade GUI, but it can still be made visible by importing this sample Pomfort Look File (*.plf). Select File -> Import Look as Shot -> Pomfort Look (plf).
Lattice
With Lattice it’s still possible to convert a 3D-LUT/Look and generate an approximation ALF1 *.xml Look file for the ALEXA Classic series. Select File -> Export Approximate -> Arri Look XML.
External LUT Box
It's also worth considering external 3D LUT boxes as an option:
AJA Color Box
Flanders Box IO
Teradek COLR
TV Logic IS mini (former Fuji IS mini LUT boxes)
Generally speaking you need to export the look as a 3D-LUT and build this into an ARRI Look File.
For ALEXA 35 this needs to be a Log-to-Log 3D-LUT based on actual LogC4 footage ("Creative Modification Transform"); the transform to Rec 709 can be either handled by the camera/ARRI Color Management or by using a custom Display Render Transform (DRT). Use the ARRI Reference Tool to create an ARRI Look File 4.
For all ALEXA and AMIRA cameras using the previous look file format (ALF-2), the look must be based on LogC3 footage. A 3D-LUT to use in an ALF-2 needs to have a transform to Rec 709 baked-in. Use the ARRI Color Tool to create the look file.
ARRI Look Library LogC3
Collection of log-to-log 3D LUTs for ALEXA Classic, ALEXA Mini, AMIRA, ALEXA 65, ALEXA LF, and ALEXA Mini LF
The ARRI Look File 2 enables different ways to influence the image on ARRI cameras. Here’s an overview on the workflow:
The in-camera ARRI Look Library files are protected. You have to rename your exported look name before loading it back to the camera. Rename the exported “1110-1.aml” file to a different filename, such as “1110-1_v2.aml” on the system to which the Look was exported.Then import the renamed look back into the camera.
There are different parameters for sharpness, detail and the ARRI noise redcution and in what way it will affect the final image. A more detailed explanation regarding all settings you will find in our ARRI Texture Control Whitepaper.
This does not apply to ALEXA 35 cameras, which have a dedicated feature called "ARRI Textures" to control the image.
The ARRI Look File 4 (ALF4) is our 3rd generation look file used in ALF4 (ALEXA 35 and later).
An ALF4 allows the use of ASC CDL as well as multiple 3D-LUTs for creative grade (Creative Modification Transform) as well as for colorspace transfomation (Display Render Transform). ALF4's can be created and extracted using the ARRI Reference Tool's LOOK room.
An Ethernet or WIFI connection to the camera is the key element in a live grading setup. We’ve created an overview to show the big picture of such a setup:
ARRI Look File 1 offers CDL-like controls as well as printer lights, saturation and a user-definable tone mapping curve. The ALF-1 does not apply LIFT/Gamma/Gain before but after the conversion to REC 709. Usually CDL is done in Log C because there’s more image information in Log C (low- and highlights) still there to work with.
ARRI Look File 2 offers full CDL and 3D LUT or Video Look Parameters. Look files in the file header can be utilized in post. The ALF2 enables support for REC 2020 (please see second question: "What is Rec 2020") and provides the option for live grading.
ARRI Look File 2 – Using the ALF2
ARRI Look File 2 - Looks in Editorial
Rec 2020 is a wider color space than Rec 709, which is the current industry standard for HD. Rec 2020 promises more brilliant images, though only new display technology is able to show these. Traditional Rec 709 displays (like TVs or ordinary computer displays) can’t display Rec 2020.
While Rec 709 (short for Recommendation ITU-R BT.709) is the encoding color space for HDTV, Rec 2020 is the encoding color space for UHD. The primary colors lie on the spectral locus and it is thus possible to have more saturated colors in images. (It does not mean, however, that all colors look more saturated. When properly converted, a Rec 709 image will look exactly the same when displayed on a Rec 2020 display.)
Rec 2020 is an encoding standard. A TV or display may not support the full gamut. Nevertheless, it will correctly display the colors within its physical gamut. To get the “Premium” logo of the UHD Alliance, for example, a TV needs to support a minimum of 90% of the P3 gamut.
Yes, since the very first ALEXA back in 2010!
Find out more on HDR in our separate HDR FAQ
As explained in the answer "What is Log C?" the maximum value of the Log C function depends on the exposure index. In a video image, however, one wants to have the clipping point of the sensor represented by the maximum signal (100%) regardless if this clipping point is 6, 7, or 8 stops above mid gray. Therefore, the LUTs for conversion from Log C to Video normalize this range, e.g. the video signal range will always go from approx. 1% to 100%.
This normalization is done always in the camera. For post-production, it’s possible to use a LUT that is computed without this normalization step, and it’s called “photometric” (the name is a bit misleading). When one works with a timeline of shots recorded with different settings of the exposure index, it’s easier to use one conversion LUT for all.
One side effect of this normalization is that you get lower blacks. Users who want to use a single LUT while maintaining the look of the image as output by the camera should use the LUT computed for EI 800.
This is an encoding where the digital values are proportional to the relative brightness in the scene. In more technical terms it’s said that the digital values are radiometrically linear. Scene Linear files are stored in a 16bit float container and are mostly used for VFX pulls.
The ARRI Look Library is available free of charge. You can download the whole package in the ARRI Look File format or as 3D-LUTs. Pick ALF-2/LogC3 for all cameras but ALEXA 35) and ALF-4/Logc4 for ALEXA 35.
To find the downloads please head to our look files website.
The Color Decision List CDL or ASC CDL) is a format for the exchange of metadata information about a basic primary color grading between the camera and post-production software. The American Society of Cinematographers (ASC) defined four functions for the CDL: Slope, Offset, Power and Saturation.
A color gamut is the range of reproducible colors available on a certain device such as a display for example. A display may have a color gamut that exceeds a certain color space which itself is a subset of the visible spectrum of the human eye.
The color gamut is described by its three primary color values (red, green and blue), which define all possible colors for a color gamut inside of a triangle spanned between these primary colors. The primary colors therefore also define the outer boundaries of the gamut of the specific device. A display cannot produce colors that are outside of its gamut.
A 1D-LUT describes a transformation applied to each of the red, green and blue (RGB) channels independently. A 1D-LUT contains an input value for each of the three colors and a corresponding output value. So for a given value of R, G, or B input, there is a given value of R, G, and B output.
This is not an error! You have chosen to record in “Log C” – ARRI’s native color encoding. Opposed to a “video” image (in REC 709 color space) Log C maintains more details in the lowlight as well as in the highlight areas. Log C is also referred to as the camera negative as it is unprocessed footage.
Here's an overview on ALF-1/ALF-2 support in 3rd party tools:
DCI-P3 color space has been removed from the ALEXA camera menu for reasons of simplicity. A conversion LUT, LogC3 to DCI-P3, can be generated via our LUT Generator.
The Log C curve is a logarithmic encoding of the scene, meaning that the relation between exposure measured in stops and the signal is constant over a wide range. Each stop of exposure increases the signal by the same amount. The overall shape of the Log C curve is similar to the exposure curves of film negatives. Because of fundamental differences between a sensor and negative film, however, the color characteristics remain different.
Log C actually is a set of curves for different EI values/ASA ratings. Each curve maps the sensor signal, corresponding to 18% gray scene luminance, to a code value of 400 (LogC3)/308 (LogC4) in a 10 bit signal. A 10 bit signal offers a total code value range of 0 to 1023. The maximum value of the Log C curve depends on the set EI value. The reason is quite simple: When the lens is stopped down, by one stop for example and the EI setting is increased from, say, 800 to 1600, the sensor will capture one stop more highlight information. Since the Log C output represents scene exposure values, the maximum value increases.
As most of the postproduction tools use their own notation for look up tables, ARRI offers conversion LUTs through the online LUT Generator (for LogC3 only! here's the LUT package for LogC4) which can create over a dozen different LUT formats.
When dailies are going to be color timed, the colorist may prefer using a photometric conversion LUT as he or she will use just this one LUT for all shots and perform adjustments to the black and white levels anyway. An example of LUT generator settings for color-corrected dailies are shown below. For an automated dailies process, the normalized LUTs must be used in order to compensate for the different ASA settings on the camera.
If „ARRI Look File 1“-looks were created and used during the shoot, they can also be converted with the ARRI Color Tool to create 3D LUTs that include look file adjustments (Choose preset "Look"). This will allow the creation of Dailies including the intended look from the DP.
"Wide gamut" is a generic term for color gamuts that are larger than Rec. 709, i.e. P3 or Rec. 2020. ARRI Wide Gamut 3/4 is the name of the color encoding space used in combination with Log C.
3D-LUTs are more powerful than 1D-LUTs as they can cross-convert colors between channels and independently control saturation, brightness and contrast. However, they are significantly larger than 1D-LUTs and require some computation, since they only store some key values and any in-between values are interpolated.
The values of the primaries in an image from the sensor of a digital camera relate to the amount of light seen through red, green and blue color filters. There are no colors a camera can’t see, so it does not really make sense to talk about the gamut of a camera. It is, however, necessary to describe the color space used to encode the colors, which in case of the ALEXA camera is called the ARRI Wide Gamut color space.
ARRI always strives to deliver the best overall image quality. As part of that we’re continuously improving our color science.
With the new ALEV4 sensor we've taken our color science through its biggest rewrite since we introduced the ALEV3 sensor in the first ALEXA in 2010. We've made various improvements over the years, but our color science never really came to a rest. In these last years LogC3 became famous throughout the industry. With ALEV4 LogC3 had to change to hold all the dynamic range the new sensor if capable of. So all is new: ARRI Color Engine, ARRI Wide Gamut 4, LogC4. To sum it up we call the new color science REVEAL.
The good news: REVEAL is compatible with ALEV3 cameras. One can de-bayer ALEV3 ARRIRAW to ARRI Wide Gamut 4/LogC4 and use all the benefits of REVEAL. If shot in ProRes – no worries LogC3 is and will be supported in all post tools through our SDK.
To get a good, correct color representation, you typically want to adjust the white balance of the camera to the lighting of your scene. As a result, the live output and recorded image of a neutral grey target should not exhibit a color cast (at least while no artistic look is applied). Since it may be difficult to see a color cast depending on the viewing environment, the best way is to look for a color shift with an RGB waveform display or a vecorscope display.
The camera offers two dials that allow you to set the white balance:
- the color temperature [K] will move the white point between blue and red, or "colder and warmer".
- the tint or color cast [CC] will move the white point between green and magenta or "plus and minus green".
You can either set these values manually or have the camera calculate an automated white balance while it is looking at the neutral grey target.
Material recorded in Rec 709 (short for ITU-Recommendation BT.709) has a display specific encoding or a, in other words, "what you see is what you get" characteristic. The purpose of a display specific encoding is to immediately provide a visually correct representation of the camera material, when it is screened on a certain display device. This is achieved by mapping the actual contrast range of the scene into the contrast range that a display device can reproduce. Examples of display specific encodings are Rec 709 for HDTV screens or DCI P3 for Digital Cinema Projectors. On the downside, a display specific encoding puts some limits on the options for a colorist.
Use the ARRI Color Tool (ACT) to create ARRI’s Look File 2 to use in ALEXA SXT, ALEXA Mini and AMIRA. Based on a Log C-clip or a *.dpx still frame you can create looks using Color Decision List (CDL) parameters, “Video Look Parameters” (VLP) or import 3D LUTs created in a grading session.
ACT is a free application for Mac and Windows computers.
Please note: The ARRI Color Tool has been discontinued. The functionality will be covered by our ARRI Reference Tool (ART) from now on.
Use ARRI Look Creator (ALC) to create ARRI’s Look File 1 (ALF1) to use in ALEXA Classic and XT. Based on a *.dpx still frame you can create look by using printer lights, saturation and CDL values.
ALC is a free application for Mac and Windows computers.
Please note: The ARRI Look Creator is end-of-life (EOL) and has been discontinued. Nevertheless there are still possibilities generating ALF1 looks for your ALEXA Classic and XT. Please have a look here...
Our colleagues of ARRI Media only sell the whole bundle.
Please ask our colleagues at ARRI Media, as they can provide the Looks for different color spaces.
No, not yet, but future releases of the ARRI Color Tool (ACT) will have the ability to preview the ARRI Look Library.
