Print Film Emulation LUT’s are generally designed by closely analyzing the Color Palette of common film stocks. Although it can be matched manually with color charts by comparing and profiling shots taken on film and digital camera. This is generally a rather complex process.
Before looking into how the film look can be emulated for digital footage let’s see how the film is processed.
An original camera negative records a scene as density within the film stock emulsion. After processing this results in the areas of the film that were exposed to bright information in the original scene being dense/dark within the film frame and areas of the frame that were exposed to dark information being less dense/bright. The film also records the inverse of the original color. Hence, the initial film recording of the image is a negative copy of the original scene.
Printing a projection print from a negative..
The level of exposure ‘seen’ by the new film stock is controlled by varying the amount of red, green, and blue light shone through the original processed negative. This is called ‘timing’ and uses values called ‘printer lights’ to define the amount of light being used. This timing process can be used when making a duplicate [intermediate positive or negative] or when making a final projection print.
For a well-exposed original camera, negative printer light values of R25 G25 B25 produce a balanced and mid-level exposed print. As printer lights are used to expose a dupe film copy or print they can control the relative density of the new film by varying the amount of light that is made available.
The difference between subtractive color and additive color is key to differentiating between the “film” and “video” looks.
Subtractive color uses, dyes, inks, or filters to absorb some wavelengths of light, which is basically what a film does.
Additive color is light created by mixing together light of two or more different colors. RGB are the primary colors normally used in additive color systems. Modern digital cameras work in this scheme type of additive RGB colors.
There are certain properties of this subtractive color model that gives a pleasing look to the film.
A quote by Glenn Kennel (Current CEO of ARRI)
“…the most saturated colors that film can reproduce are dark cyans, magentas, and yellows, each produced by a maximum density of its respective image dye, but resulting in low luminance levels. In contrast, the most saturated colors on a digital display are the bright red, green, and blue primaries, each produced by the maximum output of its additive color channel, and therefore resulting in the maximum luminance for that channel.”
— Kennel, Glenn. Color and Mastering for Digital Cinema. Focal Press, 2007. Page 22, “Unstable Primaries.”
The lighter tones are always the least saturated and very saturated tones are deeper and darker, there are other properties like film grain, halation, and gate weave..
Halation is a blurred effect around the edges of highlight areas in a photographic image caused by reflection and scattering of light through the emulsion …
Film shifts around slightly in the gate ie., the mechanical swinging of a film strip while it is being pulled through a frame window in a film camera, projector, or video coding device is called the Gate Weave and can be emulated for a film look. Gate weave/wobble is a characteristic artifact that occurs during film scanning/projection. Numerous techniques have been tried to minimize gate weave in film, using both improvements in mechanical film handling and electronic post-processing. Though sometimes this is added to emulate the look aesthetics of the film.
There are several techniques to emulate the film look for the digital footage LUTS / LMT’s (for ACES) / Third Party Plugins.
LUTs (Look Up Tables) are basically mathematical transforms. If you are going to apply LUTs to your footage, it should be in its proper color space and gamma the LUT is actually designed for.
For example, in DaVinci resolve under Film Looks in LUTS there is “Rec709 Kodak 2383 D65” which gives us information that it is a “Rec709” LUT that transforms to Kodak 2383 look. Moreover, if you open up the LUT file in a text editor you can see that the input footage gamma is supposed to be a Cineon Log for the transformation to work correctly.
Hence if you are going to apply a LUT you need to know the color space and the input footage gamma and the footage should be transformed to it prior to applying the LUT.
In the case of color-managed workflows like ACES, LUTs generally do not work right. In ACES we have LMT’s. Look Modification Transforms (LMTs) are a very powerful component of the Academy Color Encoding System and offer extraordinary flexibility in ACES-based workflows.
There are several Print Film Emulation LMT’s for ACES.
For more information on LMT’s for ACES Workflow Check out ACES Central.