Autor: Redaktion

Look Up Tables (LUTs)

Despite recent technological advances, many filmmakers still prefer the look of film.

Historically, without the use of filters or special development processes, filmmakers had to rely mainly on the photochemical properties of film to achieve a particular look. This meant that film maker had to have an in-depth knowledge of the impact of these process (eg Bleach bypass) on their rushes. 

Once digital video technology had surpassed the resolution of film and matched its dynamic range a film's look could increasingly be defined in post-production. Despite recent technological advances, many filmmakers still prefer the look of film and a new way to achieve it is shoot RAW in camera and then use a Look Up Tables or LUTs to apply preset colour spaces or palettes to the video.

A LUT is a reference file used to transform an image by mapping input to output values. It can be used to create a certain look, similar to the way Instagram or Facebook allow users to modify the look of pictures. Think of LUTs as the Instagram filters for feature films and it’s a good metaphor. Of course the application of LUTs needs to be carefully managed across a production to ensure that the final programme has a consistant look and feel.

There are different types of LUT: A 1D-LUT is commonly used to map sensor data to LOG recording formats.

To map a signal between different colour spaces (e.g. Rec709 , Rec2020 ) a 1-dimensional LUT is not sufficient: As each colour space is described by a 3-dimensional construct (e.g. R,G,B or Y,U,V) 3D LUTs are used.

In addition to this technical classification, LUTs can be distinguished by their purpose.
Technical LUTs serve the purpose of displaying a picture taken in another colour space "correctly". This is particularly useful when reviewing recordings in the field as portable monitors rarely match the characteristic of the camera used.
Creative LUTs are used to achieve certain looks (eg KODAK Filmlook).

Camera LUTs convert a signal recorded in a particular camera mode (For example, the Arri LOG-C) into a colour space (e.g. using the ARRI Alexa Rec 709 LUT, can represent the Rec709 colour space.)

A LUT will allow you to work in a specific colour space, which may be Rec.709 for standard dynamic range or Rec.2020 for high dynamic range, or in a completely different colour space. Of course it does move a lot of colour management away from location to the post production process. This gives more flexibility, but also can lead to higher costs in post production.

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