May 7, 2011

What is a Look Up Table (LUT), Anyway?

This is a guest post by producer/colorist Jay Friesen.

There are a lot of great tools out for grading and finishing. Cineform’s First Light has been out for a while now and Red Giant’s LUT Buddy was just released. Technicolor also released their CineStyle profile for Canon DSLRs and their documentation talks about using the included Look Up Table (LUT) in the post processing of your footage. The new Sony F3 will soon have a firmware upgrade that enables an uncompressed 4:4:4 S-LOG mode that utilizes LUTs. So, what exactly is a LUT?

First of all what is a LUT and what are its typical uses?

LUT means “Look Up Table.” It’s helpful to think of it like a math problem: R= S+L
“R” being your result or what you want to attain.
“S” being your source or what you start with.
“L” being your LUT or the difference needed to make up between your source and your desired outcome.

In all cases of LUT use, the LUT is the means to make up the difference between source and result.((All cases assume the colorist (or you) is grading through a correctly calibrated monitor for evaluation and finishing. LUTs in no way replace proper calibration or color correction. They only assist in the process.)) It’s never the result by itself. How does this play out? I’ll layout a couple probably over-simplified examples:

Color Correction

A very common example is printing your final film to…real, actual film. Print film came in a variety of flavors and styles. Each style had different nuances in color. The film lab would have all that nuance information or be able to send you a print test to work with. That would be your final result. The colorist grades a picture on his calibrated monitor but if he were to send that to print, it could come out looking far different due to the nuances of the physical film.

So in our math analogy, his graded film is “S” and his film print is “R.” He then uses the information from the film lab or on his own, creates and applies the LUT or the “L” to get him from his graded film to the print and to have it look as intended after it’s on the physical film. After applying the LUT, his graded film may look awful on his monitor, but will come out correct on the film print.

Color Calibration

The other option our colorist could take is to apply his film information to his monitor first -- before starting in on his color correction -- so he’s grading as if his movie is already on film. It looks good to him on his monitor now, but if he were to grade the entire film and then upload it to the web or play a different project through his monitor, it wouldn’t look correct because he applied his LUT to his monitor first. While this is a common method to calibrate monitors for normal REC709 and P3 grading, that’s more advanced than I want to get into right now.

Summary

The key takeaway here is that LUTs are not used to creatively grade a final result, they’re used to make up a difference between a source and a result. In practical application -- with the CineStyle profile, for instance -- the LUT will let you view your footage during editing more naturally than the flat, desaturated image originally recorded. However, it’s best to remove it for final color grading and rely on your properly calibrated monitor to tell you what color it is and yourself to determine what color it should be. If not used carefully, improper LUT use could screw up your footage or limit your image manipulation options in post.

Nobody says you can’t apply a LUT for a creative grade, but be forewarned: if your shots don't match each other to begin with, they're not going to match after you’ve applied the LUT. In this instance, you’ve basically turned the LUT into a glorified color correction filter, which is not what it's intended to be.


Jay Friesen is a professional colorist with a Davinci Resolve for Mac suite with LUT Calibrated Plasma and SXRD projection technology, working out of his house because it's cooler to work from home. Enabling productions via a massive network of professionals for full-range projects. This post originally appeared in a slightly different form on his blog.

Your Comment

15 Comments

Its so much informative. Thank you . .

May 8, 2011

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Great article, many thanks.
Colour correction/grading is something I really have a hard time with, so tidbits like this are gold!

May 8, 2011

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Leighton

Great article, and a succinct explanation of how to use a LUT during grading.

May 9, 2011

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Great explanation! Nobody explains it like you guys!

May 9, 2011

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John

Good to know that it isn't an easy fix for CC. What are you guys using for monitor calibration?

May 9, 2011

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Anonymouse

I made a quick video on how to use LUT Buddy with Final Cut Pro. http://philhoyt.com/how-to-use-the-cinestyle-lut-with-final-cut-pro

May 11, 2011

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Thanks a lot! I just went through the whole procedure with the cine-style LUT. It looks perfect!

I just wonder.. Is it normal that a 1,5 minute clip needs a rendering time of 10 minutes? That will slow any project down a lot…

(Phil, Thanks for your video.. I re-typed my question here..)

May 11, 2011

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Ronald Jensen

thanks! all us newbies dont know what the hell this LUT is but we still want the extra latitude
i love this site!

May 12, 2011

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mendel

What drives me crazy is that most video editing software (Premiere up to CS4 and FCP up to 6.x) doesn't seem to have to most basic color profiling at all.
When using a well calibrated wide-gamut monitor, all the editing software will show oversaturated colors, while even the cheapest little picture viewers or browsers like mozilla support a 100% correct profiling for still pictures.

I have a 2010 MacPro at work with a new 27" cinema display, I'm using FCP 6.x (not sure about the exact version right now, sorry) and even the gamma doesn't match at all. All shots look too dark on the monitor and get much brighter once you encode them and view them with an external player.

All the pro video guys at dvinfo or elsewhere have to offer, is tell me that I need a thousands of dollars break-out card and an even more expensive class a monitor to get it right...

It is so annoying, because with my 700 bucks Dell monitor and a 150 bucks spyder 3 I can get professional results for still pictures, but I am just lost with video editing...

At first I thought this article is going to address that problem, but it isn't really.
I am curious, are the very newest versions of FCP and/or Premiere finally capable of working with a calibrated monitor? One should think so, but they should've been for years and they weren't, so I'm a bit sceptical...

May 12, 2011

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Heiko

when you say "it’s best to remove it for final color grading" do you mean apply the LUT plugin then color grade then remove or disable the LUT plugin from the time line or clip so it's not included in the export process?

May 13, 2011

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Kadshah

Forgot to mention my monitor is calibrated with spider 3.

May 13, 2011

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Kadshah

For a good level of LUT info see: www.lightillusion.com/luts.html

Also download LightSpace CSM to play with LUT generation and application.

Steve
(Hi Jay!!!)

March 25, 2012

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Really good article. I was at NAB this year and came across OSEE Americas, they manufacture most of the Professional monitor that get rebranded by (Wohler and Marshall and other companies) they just launched as a company in the US, and their monitors are Centered on LUT import capabilities. Do you think this will get rid of the Grading in Post Production - as you can just apply at LUT on set, see your end product, and then reapply the same LUT through post?

For a person like myself who doesn't have as much experience in grading: buying a Monitor for production that allows me to apply LUTs - so I can shoot raw and still see my end image - and having the option to download various LUTs from professionals to load into my Monitors and Editing programs just seems like the best option.

Basically do you feel like this will eliminate jobs, make work easier, and open up the idea of having a Professional monitor on every set - as opposed to some Liliput monitor?

September 5, 2014

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Kyle
8

You're thinking about LUTs in the entirely wrong way. They are correction algorithms for translating the color footage in a non-destructive way.

Usually in a professional setting this means you apply a LUT in post to a) make your RAW files look normal (file LUTs) and then to b) translate that 'normal' footage so it looks normal on any display device (view LUTs).

For example if you have Arri RAW footage you might apply a Arri Log->Lin file LUT to it which flattens out the sLog curve specific to the Arri camera sensor into a 'neutral' straight linear colour space. This 'normal' image will look weird on your monitor though so then you apply a view LUT that makes any 'normal' image display like Rec 709 on your monitor. The idea here is you could also take RED footage, apply the RED gamma4/colour4 log->lin file LUT and it would now be 'normal' as well - this allows mixing of footage from different sources or for different creative decisions from DPs.

The point of normalising the footage with the file LUT is that you can now creatively colour something and it can be displayed (with a view LUT) on any calibrated monitor/device and it'll look the same.

It is possible to create specific LUTs that perform more creative colouring decisions but this is pretty much exclusive to the domain of visual effects where a Look needs to be exported for compositing artists to match.

Apart from that specific circumstance applying the file LUT just gives you the Base Footage (normalised or otherwise) from which you can begin grading - it's the step before your neutral grade in most workflows and certainly it comes before creative colour adjustment.

It does get more complicated, you can perform both steps at once for instance by using 3D luts that log->lin or vice versa then display or convert for display yada yada but most of the time it's pretty much each type of footage (camera) needs a certain file LUT and then you use view LUTs so that you can make meaningful colour decisions even if you can't look at the final destination monitor.

January 7, 2015

1
Reply
wil manning
vfx supervisor
13

You're thinking about LUTs in the entirely wrong way. They are correction algorithms for translating the color footage in a non-destructive way.

Usually in a professional setting this means you apply a LUT in post to a) make your RAW files look normal (file LUTs) and then to b) translate that 'normal' footage so it looks as one expects it to on any display device (view LUTs).

For example if you have Arri RAW footage you might apply a Arri Log->Lin file LUT to it which flattens out the sLog curve specific to the Arri camera sensor into a 'neutral' straight linear colour space. This 'normal' image will look weird on your monitor though so then you apply a view LUT that makes any 'normal' image display like Rec 709 on your monitor. The idea here is you could also take RED footage, apply the RED gamma4/colour4 log->lin file LUT and it would now be 'normal' as well - this allows mixing of footage from different sources or for different creative decisions from DPs.

The point of normalising the footage with the file LUT is that you can now creatively colour something and it can be displayed (with a view LUT) on any calibrated monitor/device and it'll look the same.

It is possible to create specific LUTs that perform more creative colouring decisions but this is pretty much exclusive to the domain of visual effects where a Look needs to be exported for compositing artists to match.

Apart from that specific circumstance applying the file LUT just gives you the Base Footage (normalised or otherwise) from which you can begin grading - it's the step before your neutral grade in most workflows and certainly it comes before creative colour adjustment.

It does get more complicated, you can perform both steps at once for instance by using 3D luts that log->lin or vice versa then display or convert for display yada yada but most of the time it's pretty much each type of footage (camera) needs a certain file LUT and then you use view LUTs so that you can make meaningful colour decisions even if you can't look at the final destination monitor.

January 7, 2015

0
Reply
wil manning
vfx supervisor
13