Restricted Illuminants
When I set about creating this collection, a use case that emerged outside of the library of nice references was the ability to see techniques or trends where I wasn’t able to previously see them. One such technique that I noticed was what I would call “Restricted Illuminants”. This is an idea that I have been sitting on for a while and, following presentations from FilmLight Image Engineer Daniele Siragusano at Camerimage as well as the UP.GRADE Crosstalk seminar, I thought it was about time to put them out into the world.
I am hoping to start a bit of conversation around this idea - but I think to understand the basics of the technique it is important to understand the three key components that enable it to work. The first and most obvious component is the content. All content is created and delivered to certain standards and those standards usually define an available luminance range. Second is the human eye - primarily that our vision system is built to adapt, and the third component is the environment that this all takes place in. Where all three of these come together to create the effect is in the cinema. Here the DCI cinema standards give a luminance range with a maximum illuminant of 48nits. The viewing environment is also much darker and more controlled than most television environments. In the case of a cinema, the primary source of illumination is the screen we seen in front of us (and hopefully not too much pollution from green exit signs). If the brightest thing in a room is the white on the screen then our eye adapts and adjusts to this. This is where the use of a ‘restricted illuminate comes in to play. If the content of a film only uses 75% of the available luminance range then when projected in a cinema our eye will adapt to the lower luminance levels from the screen. This adaptation now becomes our new illuminance reference - the content on the screen is still the brightest thing in the room as we don’t have pollution from other light sources in the viewing environment.
There are films in the library that use this technique and it quickly becomes apparent when the entire range of available luminance is not in use - just by looking at the waveforms. One film that cleverly restricts the illuminate levels is Arrival (2016).
Almost the entire film's highlights are restricted. When watching the film in context, it isn’t particularly noticeable - the film just has a low contrast mood. The additional headroom in the luminance range is reserved for select scenes, where the whole range is used.
As a result, these scenes seem remarkably bright and strong and when compared the rest of the film they really stand out. The impact is increased in cinema viewing environments, as the eye has already adapted to a lower white point.
This isn't the first time that director Denis Villeneuve has used this effect. Similar techniques were used in the 2015 film, Sicario.
Here though, the highlights feel clamped much harder than in Arrival. The impact here is different too; the clamping emphasises the intensity of the dry harsh environment. I even found myself squinting into highlights when seeking out details during external scenes - no doubt the same reaction I would have if I were actually standing on set.
Yet another, but very different example of restricted illuminant is Repo! The Genetic Opera. This highly stylised film also keeps highlights pinned below the maximum possible level. There are glimpses of brighter elements, mostly during the animated sequences.
During the live action, the restricted illuminant is largely part of the style. Given the strong visual style of the film it got me thinking about the relationship between the maximum illuminant and saturation. Traditionally, as you approach the maximum illumination point, saturation is lost. by using a restricted illuminant though perhaps it would be possible to have both a “maximum” illuminant and saturated colours.
Again, it is important to note that all of these examples are from features with cinema release as their primary destination. While we may not be viewing them now in the same controlled environment but it is possible to see how it lends itself well to manipulating the adaptation of the viewing audience. It'll be interesting to see if these techniques persist into HDR mastering, which would seem to go against the increase in available luminance range.
To see more stills from the feature films, click below.
EDIT: I am open to suggestions for naming this technique, other suggestions included Restricted Use of Maximum Luminance, Restricted Maximum White Point Luminance or Capped Highlights.