The Arri LUT Generator – Part 2

Understanding the Arri LUT Generator: Do’s and Don’ts

January 8, 2014

Learn how to create LUTs for the Alexa using the official Arri LUT Generator. Develop your own set of best practices when working with this tool.


Series

Understanding the ARRI LUT Generator: Part 2

In Part 1 of this series, I showed how you can creatively work with a dozen different LUTs from the ARRI Lut generator. That Insight is somewhat of a culmination of our LUT series, teaching one way of thinking about and using Look Up Tables creatively.

This Insight will take a close look at ARRI’s online LUT Generator for the Alexa. It’s designed to be used with ARRI RAW or ARRI Log-C recorded images for viewing and color correcting in the HD color space.

If you’ve watched my earlier Insights on LUTs you’ll know that I consider LUTs an optional tool. I’ll use a LUT when it makes my job easier, faster and the final image more interesting. If I find the LUT either slows me down, is difficult to work with or just doesn’t get me very interesting results then I’ll abandon it.

And this brings us to the ARRI LUT Generator, a unique tool among camera manufacturers – and a tool that is frequently misunderstood by post-production professionals. This Insight is about understanding the Arri Alexa LUT Generator.

What is the ARRI LUT Generator?

The ARRI LUT Generator is an interactive online tool for creating all sorts of files that you’d want to use when shooting with the ARRI Alexa – especially if you’re recording or color correcting ARRI RAW or ARRI Alexa Log-C footage. It can generate files to upload to ARRI cameras, a reference monitor, editing software, compositing software, and color correction software.

It’ll output just about any file format you’ll need to just about any app that needs them.

As to the question: Why would you want to use a LUT other than the one that might ship with your software? Here’s a quote from ARRI’s website:

There is a certain degree of freedom when a Log C image is rendered for display. The situation is similar to choosing a print film. You may prefer a more contrasty or a softer look. You may prefer fully saturated colors or the bleak look of a bleach bypass process.  Therefore, using a 3DLUT with a custom look is a perfect alternative to using the LUTs provided by ARRI.

If ARRI thinks there’s a good reason why you might not want to color correct with ANY of their LUTs – surely they think it’s a good idea to experiment with more than just the one standard Alexa LUT that ships with many software apps? I sure do.

Finding the LUT Generator
The ARRI LUT Generator is a bit buried on their website. It can be found on their homepage in the Digital Camera > Tools section of their website. Once you click through to the tool, you’ll need to agree to hold them harmless and then it’ll load up for you:

Screenshot of the ARRI LUT Generator
This Insight is focused on the ‘Postproduction’ sub-tab of the ARRI LUT Generator.

The Postproduction Tab

This Insight focuses on the Postproduction tab of the LUT generator. We’ll be exploring two things:

  • The pulldowns and checkboxes  you DO change
  • The pulldowns and checkboxes  you DON’T change (unless you have a darn good reason)

The LUT Generator itself isn’t all that hard to understand, it just takes a little getting used to. While I won’t be covering in detail every little ‘knob and switch’, you can get that kind of detail off ARRI’s documentation section of their website. In particular, you will want to read the following for total mastery:

  • [pdf] Alexa Dailies using DaVinci Resolve 9: This document is a great reference for understanding if you should generate Legal Range or Full Range LUTs (hint: the latter). Of course, it has a ton of other useful information (but is outside the scope of this Insight).
  • [website] Alexa Color Processing: This is a fantastic resource on ARRI’s website that will systematically teach you about ARRI Log recording and display. Click on the Alexa Log C Workflows sub tab for specific advice on using the LUT Generator.

Learn how to use the ARRI LUT Generator

This Insight will cover several aspects of using the online LUT Generator:

  • Navigating the LUT Generator
  • What the most useful options do
  • The most common elements I change
  • Why I leave other parameters unchanged
  • Saving custom LUTs

In the near future, I’ll have a third part to this series showing you how to import these LUTs into the most widely used color correction and non-liner editing apps.

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Comments

6 thoughts on “Understanding the Arri LUT Generator: Do’s and Don’ts”

  1. For in camera custom made LUTS can you use the extended to extended range (EE)? As the output from camera will be legal then will go to the custom LUT what is (EE) is basically the same just data level – then it stays at extended for post software aka resolve what use data levels not video levels, making it all match up?

    1. This is totally dependent on both the camera and the post production software. It’s impossible to generalize an answer other than: Test the workflow before production begins to be sure the LUT you deliver from camera works in the software being used.

      In most cases, it’ll work and you don’t have to worry about the Legal vs Data levels because well engineered software handles this transparently for you. And if the software doesn’t, you want to catch this before production begins since the fix is usually as easy as picking a different codec or setting a ‘flag’ in software so the footage is interpreted correctly.

      1. Thanks Patrick – So say I will be grading the dailies at the end of the day in resolve but the DOP wants to see the custom LUT in camera on his EVF or monitor to exposes to – I am safe to use the EE LUT in camera as a viewing LUT over the log – c image with the camera set to legal output – to get the correct signal for the DOP and 1st AC – Then when I get the footage I will use the same EE LUT in resolve and all the levels should match up ? As RGB Data Levels “extended” 0-1023 will always be output of 0-100% Video Levels so it would not affect or clip in camera – so what the DOP is seeing is what I will be seeing.

        1. Hi Luke,
          Let me jump into this conversation. As I DIT I come across this often. Technically the answer to your question is yes, the EVF, the AC’s 7″ and your monitors should show the same image when sharing that LUT.

          BUT….

          And you knew there’d be a but, it really depends on if all three monitors are looking at the same gamma / contrast / brightness settings. Cameras don’t often let you adjust the contrast of the EVF and I know many a 1st AC who has cranked the hell out of their monitor so they can pull focus on a 85mm with the stop wide open.

          What you should do is be at the camera prep day and take an hour to test the LUT on the monitors not only to see if they all look the same but if the DP and the 1st want to see them. I just worked on a show this summer where we noticed that camera, 1st’s and my monitors where all a different brightness. I convinced production to let me come in early to properly calibrate the 3 monitors. At the first set up that day both the DP and the 1st wanted their monitors turned back to where they had them before. We spent the rest of the shoot where the DP and Gaffer looked at my monitor for lighting adjustments and he and the 1st just used there own setting to operate.

          Good luck with the shoot.

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