LUT is an abbreviation for Lookup Table. This term is used quite often in today’s digital post and pre/production worlds, but if you were to ask anyone in the field you’d be surprised to find that so few really understand what the term means.
In essence though, and especially with regard to video editing, a LUT is a means of translating colors and colorspaces, from one to another.
Table of Contents
- LUTs are not filters or color presets.
- LUTs are technical/scientific colorspace transforms (when used properly).
- LUTs can severely degrade and negatively affect your image if improperly used.
- LUTs are not for everyone and should be used only when required or desired.
What is the Purpose of a LUT?
There are many ways in which a LUT can be applied and used throughout the production and post-production process. We’re going to focus exclusively on their usage and application through video editing/color grading.
In the post-production domain, LUTs can be used to simulate the response and color reproduction of various film stocks, to shift color from RAW/LOG spaces to HDR/SDR, and also (as they are most commonly, and rather improperly used) to apply a familiar Hollywood Blockbuster look to your own film.
When used correctly the results can be quite pleasing and desirable, especially when a LUT is built from scratch for a production ahead of time, in tandem/concert with the Colorist who will be overseeing the ultimate correction and grading work of the show or film.
The purpose here is to provide the production/cinematography crew with a LUT they can load into their camera (or monitor) in order to better gauge how the raw footage will look in the end. This helps everyone visualize and light better, and generally expedites the end process through editorial and color grading stages.
LUTs are also quite helpful when handling a considerable amount of Visual Effects related footage, and exchanging the shots between various artists and companies who are all trying to work on the final frame, but may need to have the flexibility to toggle between RAW and “finished” looks on the fly.
What Information is Stored in a LUT?
The information stored in a LUT largely depends on the amount of transformative color mapping and tone mapping that is being applied and thus written into the Lookup Table.
In other words, if you aren’t modifying the color mapping, but only adjusting the overall tonal curves, then you wouldn’t (or shouldn’t) see any change in color when previewing and applying the LUT whether to the camera or in your edit/color suite.
They are merely containers and only retain that which is modified, or translated.
Note that LUTs are rather simple (even if they can be immensely powerful) and do not and cannot accommodate anything that is done through secondary/isolated color modifications (whether through PowerWindows or Qualifiers or elsewhere) and will not preserve any noise reduction, or other optical post effects.
Simply put, they are meant to be an index of color and light values, which is then applied to the raw source, and this transformation and translation they effect ultimately reflects the changes/modifications that are specified directly within the LUT, and nothing more.
Different Types of LUTs
As stated above, there are many different types of LUTs. Most readers are undoubtedly familiar with the LUTs that are used to apply familiar film looks to their films. Your mileage with these LUTs will vary depending upon the quality of the LUTs you are using (or buying) and also the way in which you are applying these LUTs and the quality of the source footage you are applying the LUT to.
One of the most important uses of LUTs is the “Show LUT” which may sound like the same thing as above, but is really anything but. Here the primary difference is that a certified Colorist has worked in tandem with the Cinematographer and they have gone through considerable effort to workshop and test their LUT to ensure that it is performing as desired for the conditions they are anticipating on set, and often create a handful of variants for all manner of lighting and time-of-day conditions.
Another oft-used and quite common type of LUT (and one that is often improperly used) is the Film Stock Emulation LUT. You have no doubt seen a slew of these, and again, your mileage may vary in how they perform or don’t, but again it all comes down to quality of the build, and the means and order of operation in applying the LUTs that dictates how well they perform, and whether or not you are sacrificing image quality or not.
There are also 1D vs. 3D LUTs but you needn’t worry too much about their differences unless you are seeking to generate one of your own. Perhaps we will cover this process and the pro’s and con’s in a future article, but at present, it exceeds the reach of this introductory article, and may just confuse you more than inform you prior to gripping the fundamentals of LUTs.
When to Use LUTs
LUTs can be used at any point in time, and are non-destructive as well (providing you are not rendering/exporting with them applied).
As stated above, LUTs are often used on-set and in-camera, or even on a production monitor (though they should never be doubled, take care not to do so). If they are so, these LUTs are usually carried through into post-production stages and applied to clips in the NLE, and/or Colorsuite.
If they are not used from the beginning, they can also often be used to get a rough look or transform out of the RAW/LOG space in the NLE (ex. R3D RAW to Rec.709).
And they can be further applied and used in the Colorsuite to varied effect, whether using ACES or some other color space, or to emulate a desired analog Kodak/Fuji film stock.
There are a lot of proper and desirable uses of LUTs, and certainly more than we have room to list and enumerate here, but there are just as many improper uses as well.
When Not to Use LUTs
If you happen to search the internet for LUTs, you will invariably find a sea of artists and advocates for using them, and almost as many detractors and die-hard haters of LUTs. To be perfectly honest, I’m generally an adherent of the latter camp, though when necessary and applied correctly, I ally with the former camp wholeheartedly.
It is generally a very poor and unprofessional route to stack and use multiple creative LUTs and to further grade on top of these color transformations. The quality loss you will experience and the severe crushing of color and luminance values will be downright awful if you do so.
Using LUTs to chase certain film grades (not the same as film stocks) is also a bad idea, despite the fact that so many people do so, and pay a fair price for these “looks”.
I realize some may counter and say that I’m wrong, but the fact remains, you are likely not shooting on the same camera with the same lighting and lenses and conditions that these films were shot on/under, correct? If you’re being honest, the answer is “no” and so, while you can certainly use these “look” LUTs and get something that may or may not look like it is in the same universe, it’s safe to assume that you won’t be spot on or even close, unless you can replicate the same in-camera settings/lighting/etc as they had.
Your mileage may vary, especially if you are using a Hollywood-grade camera, and have sufficiently experimented in order to get the “look” LUT to perform as advertised/intended, but I would wager that exceptionally few will have the determination and resources to do so.
Generally speaking, LUTs shouldn’t be applied haphazardly or if the project or footage cannot support the technical/color transformation. And using them to chase looks is not a professional way to shoot or grade your project whatever it may be.
Here are some other questions you might have about LUTs.
Are LUTs just filters or presets?
No, LUTs are scientific colorspace/luminance index transformations that are not broadly or universally applicable in the way that filters and image presets are. They are not shortcuts and they are certainly not a “magic bullet” for your footage.
Coloring and editing in this way can often greatly affect your footage and not in a good way.
Do filmmakers use LUTs?
Film professionals most certainly do use LUTs, and often at all of the various stages of the production and post-production processes. They are most commonly used on digital cinema cameras in order to achieve a specific analog film stock’s color/tonal response.
What software uses LUTs?
LUTs are used and applicable through every major NLE and Color Grading software, and you can even apply them in Photoshop as well. They are not exclusively used in the video/film domain as they are technical/scientific colorspace transformations used in a wide variety of applications along the imaging pipeline.
By now, you’ve either learned a great deal about LUTs or perhaps you’re upset with my assessment of the value of “look” LUTs. Whatever the case may be, I hope you understand that a LUT is not a panacea, or cure-all for your footage, and they are most certainly not filters or presets.
LUTs, from their generation and build to their usage throughout the entire imaging pipeline, command and demand a great deal of technical and scientific expertise and understanding with regard to color and luminance manipulation (and more) in order to ensure their proper and effective use.
Hopefully this doesn’t dissuade you from using them, as they are vitally important and immensely powerful when properly built and used, but they do require a fair amount of experimentation and research in order to use them effectively, and should be considered an advanced, master-level tool.
The more you learn about LUTs, the more capable and knowledgeable you will become overall with regard to color grading and image science as a whole. Which can be a highly desirable skill in today’s post-production market, and one that can pay you dividends for years to come.
As always, please let us know your thoughts and feedback in the comments section below. What are some of the ways in which you LUTs in your edit, color grade or on-set? Have you had bad experiences using LUTs as presets/filters?