Throughout film history directors, cinematographers, distributors, and exhibitors have engaged in a fierce battle of wills over the shape and size of projection formats. The history of aspect ratios is as fascinating as it is confusing.
In theory, digital cinematography and filmmaking tools should afford us more options than ever before, but the practical realities of a global media supply chain have forced some bitter compromises. To provide the basis for a robust and open standard, maintain compliance between vendors, and provide the viewing public a consistent experience across platforms, our choices are often limited to one of a few subsets of resolutions and aspect ratios. Digital cinema is no different. Here we’ll explore some basic considerations when choosing the correct aspect ratio for your digital cinema master.
The Cinema Screen
Not all screens are made equal. Just as aspect ratios have changed over time, so have the theaters in which they are exhibited. Some screens are narrow, some are wide, and some are even curved. Many screens are even explictly built for a particular format, like IMAX or the Cinerama Dome in Hollywood, CA. The vast majority of modern cinema screens, however, can be divided into one of two categories: FLAT and SCOPE.
Flat (1.85:1)
Scope (2.39:1)
A simplified way of understanding the distinction between FLAT and SCOPE aspect ratios, has to do with their film projection roots. Historically, FLAT films were projected with spherical lenses while SCOPE films were intended to be projected with an anamorphic lens. While both are technically widescreen formats, SCOPE films could be projected considerably wider, filling an audience’s peripheral vision and making a film even more engrossing and larger-than-life. These aesthetic advantages can only be fully realized, however, with a screen optimized for SCOPE projection.
Digital cinema no longer uses anamorphic lenses except in very specific circumstances, but we still use FLAT and SCOPE terminology to distinguish optimal projection specs for each type of screen. Everything from construction of the theater to masking and automation ultimately get determined by this distinction.
The Digital Cinema Sensor
To understand D-Cinema aspect ratios, it’s best to first understand the maximum capabilities of a projector. DCI projectors are equipped with either a 2K or 4K imaging chip. These chips each have a maximum resolution of either:
4K: 4096×2160
Digital Cinema Packages are conformed for one of the following “containers”:
| FLAT (1.85:1) | SCOPE (2.39:1) | FULL (1.9:1)* | |
|---|---|---|---|
| 2K | 1998 x 1080 | 2048 x 858 | 2048 x 1080 |
| 4K | 3996 x 2160 | 4096 x 1716 | 4096 x 2160 |
When an aspect ratio does not fit in one of the containers listed above, it will be letterboxed, pillarboxed, or resized to fit.
*The FULL container resolution is the maximum resolution that can be achieved using a 2K or 4K DCI projector. It is seldom used as the majority of flat screens are masked for 1.85:1.
Full Sensor vs. Screen Area
In order to project across the full screen area, the projector lens focal length is adjusted to fill the screen vertically for FLAT screens and horizontally for SCOPE screens. Screen masking is intended to absorb excess light to give the impression of a perfectly edged frame.
Mismatched screens and aspect ratios
Because cinema is unique from TV in that your projection format and the screen itself can have different aspect ratios, anticipating how your film will look in different screening environments is crucial if you want consistent and optimal projection for your audience. Here are the two basic scenarios you’ll need to consider:
Running into either one of these situations is unavoidable. If you’re lucky, your exhibition venue will have masking equipment to properly frame your film but the likelihood is slim. Many theaters are not equipped with adjustable masking and those that are will often neglect to use it for one reason or another. In either case, you can still fill out the screen as best possible by maximizing the horizontal or vertical resolution in your container of choice. A little more on this in a bit…
So what do you do when your aspect ratio doesn’t match the exact specs of a FLAT or SCOPE container? You probably already guessed it: letterboxing and pillarboxing. Perhaps the most common usage of this is getting HD content to play in a FLAT container.
Choosing the Right Container
The most common mistake made when mastering your finished film for cinema is choosing the wrong container for your film’s native aspect ratio. When paired incorrectly and played on the right screen, films can double up on letterboxing and pillarboxing to create a “floating window” window look.
In the left example, a SCOPE film is placed in a FLAT container with letterboxing and projected on a SCOPE screen. When projected in this fashion, the effective scaled resolution results in a full 40% loss in screen real estate. In the right example, a less common FLAT film in a SCOPE container on a FLAT screen. This can be seen at times in films that mix aspect ratios. Here screen real estate is reduced by 42%.
When in doubt, play by this simple rule of thumb:
FLAT containers should avoid Letterboxing
SCOPE Containers should avoid Pillarboxing
Ideally, your film matches up perfectly with one of the aspect ratios listed above. In most other cases your aspect ratio will likely be “close enough” to make the decision easy. For instance, a 2.4:1 aspect ratio image make the most sense in the 2.39:1 SCOPE container. Some aspect ratios, like the infamous RED 2:1, are a bit trickier. It’s a great choice for filmmakers looking to capitalize on the maximum resolution available to them, but a problematic choice for distribution. Neither FLAT nor SCOPE offers a truly optimal solution here:
If packaging in a FLAT 2K container:
- Container Resolution: 1998×1080
- Scaled Image Resolution: 1998×998
- Resolution lost to Letterbox: 7.6%
If packaging in a SCOPE 2K container
- Container Resolution: 2048×858
- Scaled Image Resolution: 1716×858
- Resolution lost to Pillarbox: 16%
The choice would appear to be pretty clear cut here as well, but there is an important variable to consider in this circumstance: screen aspect ratio. The letterboxing of this picture is fairly significant in a FLAT container. It’s important to consider how your audience will receive this when projected on screen.
Other Considerations
Can I master my DCP in both FLAT and SCOPE?
The only material that is usually required/recommended to be delivered in both FLAT and SCOPE containers are trailers. This is because trailers are intended to play in sequence with the same container size as the feature film they precede. The less confusion you can create for a projectionist the better.
Can’t the projectionist make adjustments?
Possibly, but don’t count on it. Most projection setups are heavily automated and have only a few presets available. Even then, most projectionists don’t like to court uncertainty. It’s also unlikely that special instructions like this will even reach the appropriate party as the person who ingests your film may be separate from the person who assembles your playlist and plays it back.
What if I want to put my subtitles in the letterboxing?
It’s an easy choice when making a Blu-Ray, but you have significantly greater options when making a DCP. Consider creating XML subtitles projected over image before sacrificing significant screen real estate unnecessarily.
I like the letterbox look. We’re only playing on a FLAT screen. Can’t we keep it that way?
Because of masking, theaters don’t really have a letterboxed look, per se. Rest assured that a SCOPE film whether packaged in a FLAT or SCOPE container will look pretty much the same on a FLAT screen. It’s when projected on a SCOPE screen that you run into issues.