Anamorphic widescreen
|
|
Anamorphic widescreen is a cinematography and photography technique for capturing a widescreen picture on standard 35mm film. It can also refer to a related technique for maximizing picture quality in DVD video recordings.
Anamorphic_lens_illustration_without_stretching.jpg
Anamorphic widescreen in cinematography was first popularized with CinemaScope, which was one of many widescreen formats developed in the 1950s. The need for anamorphic widescreen arose due to an incompatibility between the aspect ratio of the photographic film, and that of the resulting picture. One common widescreen format has an aspect ratio of 2.35 to 1, meaning the picture width is 2.35 times its height. 35mm film has an aspect ratio of 1.37 to 1, which is not as wide (or, conversely, is too tall). If the picture is recorded on film so that its full width fits within the film frame, some film recording area is wasted on portions that will not be visible in the finished film (Figure 1).
To make full use of the available film, an anamorphic lens is used during recording; this lens effectively stretches the picture vertically so that it fills the available film area (Figure 2). Since a larger film area is being used to record the same picture, quality is increased. The distortion introduced in the picture must be corrected when the film is played back, so another lens is used during projection that returns the picture to its correct proportions.
It may seem that it would be easier to simply use a wider film for recording movies; however, 35mm film was already in widespread use, and it was more economically feasible for film producers and exhibitors to simply attach a special lens to the camera or projector, rather than investing in a new film format, along with the attendant cameras, projectors, and editing equipment.
VistaVision and Cinerama were earlier attempts to solve the problem of incompatible aspect ratios, but anamorphic widescreen eventually proved to be more viable.
The most common anamorphic widescreen film format in use today is commonly called scope or 2.35:1 (sometimes 2.39:1 or 2.4:1). It uses a 2:1 anamorphic projector lens that expands the image by exactly twice the amount horizontally than vertically. This format is essentially the same as CinemaScope except for minor technical differences.
There are artifacts that can occur when using an anamorphic camera lens that do not occur when using an ordinary spherical lens. One is a kind of lens flare that has a long horizontal line usually with a blue tint and is most often visible when there is a bright light, such as from car headlights, in the frame with an otherwise dark scene. This artifact is not always considered to be a problem. It has come to be associated with a certain cinematic look and is in fact sometimes emulated using a special effect in scenes that were not shot using an anamorphic lens.
Another characteristic of anamorphic camera lenses is that out-of-focus elements tend to be blurred more vertically. An out-of-focus point of light in the background will appear as a vertical oval rather than a circle. When the camera shifts focus, there is often a noticeable effect where elements appear to stretch vertically when going out of focus. An anamorphic lens will also have a more shallow depth of field compared to a spherical lens for a given aperture.
While the anamorphic scope widescreen format is still in use as a camera format, it has been losing popularity in favor of flat formats, mainly Super 35. There are several reasons for this:
- An anamorphic lens can create artifacts as described above.
- An anamorphic lens is more expensive than a spherical lens.
- Because the anamorphic scope camera format does not preserve any of the image above and below the scope frame, it may not transfer as well to more narrow aspect ratios such as 4:3 or 16:9 for full screen television.
- Film grain is less of an issue because of the availability of higher quality film stocks and digital intermediates.
Anamorphic scope as a printed film format, however, is well established as the standard for 2.35:1 widescreen projection. Regardless of the camera formats used in filming, the distributed prints will be in anamorphic widescreen format. This is not likely to soon change because cinemas around the world already have an investment in the equipment to project this format.
Other widescreen film formats (commonly 1.85:1 and 1.66:1) are simply cropped in vertical size to produce the widescreen effect, a technique known as masking or hard matte. This can occur either during filming, where part of the picture is masked out in the gate, or in the lab, which can optically create a matte onto the prints. Either method produces a frame similar to that in Figure 1. Many film prints today have no matte, though the film is framed for the intended aspect ratio; this approach is called full frame filming. In these, the film captures additional information that is masked out during projection in the projector gate, known as soft matte process. This approach allows filmmakers the freedom to include the additional picture in a 4:3 transfer of the film and avoid pan and scan, though doing so may introduce areas of the picture that were not intended for viewing, such as microphone booms or other filming accessories that would not have been visible in the widescreen frame. For this reason, often productions will "protect for 4:3" by making certain the frame is clear of these objects, even though that part of the image will not remain visible in the theater.
2.35, 2.39, or 2.4?
One common misconception about the anamorphic format concerns the actual number of the aspect ratio itself. Since the anamorphic lenses in virtually all 35mm anamorphic systems provide a 2:1 squeeze, one would logically conclude that a 1.37 full academy gate would lead to a 2.74 aspect ratio if used with anamorphic lenses. However, due to a difference in the camera gate aperture and projection mask sizes for anamorphic films, the image dimensions used for anamorphic film vary from "flat" (spherical) counterparts. To complicate matters, the SMPTE standards for the format have varied over time; to further complicate things, pre-1957 prints took up the optical soundtrack space of the print (instead having magnetic sound on the sides), which made for a 2.55 ratio.
The first SMPTE definition for anamorphic projection with an optical sound track down the side (PH22.106-1957), made in December 1957, standardized the aperture to 0.839" by 0.715". The aspect ratio for this aperture, after a 2x unsqueeze, rounds to 2.35. A new definition was created in October 1970 (PH22.106-1971) which made the vertical dimension slightly smaller in order to make splices less noticable (as anamorphic prints use more of the negative frame area than any other modern format) when projected. This new aperture size, 0.838" by 0.700", makes for an unsqueezed ratio of 2.39. The most recent revision, from August 1993 (SMPTE 195-1993), slightly altered the dimensions so as to standardize a common aperture width (0.825") for all formats, anamorphic and flat. At these modern dimensions (0.825" by 0.690"), the unsqueezed ratio remains at 2.39.
Anamorphic prints are still often called 'Scope or 2.35 by projectionists, cinematographers, and others working in the field, if only by force of habit. 2.39 is in fact what they generally are referring to (unless discussing films using the process between 1958 and 1970), which is itself sometimes rounded up to 2.4. With the exception of certain specialist and archivist areas, generally 2.35 = 2.39 = 2.4 to most professionals, whether they themselves are even aware of the changes or not.
To complicate matters even further, 2.35 is often achieved by matting a flat 35mm frame or, slightly less frequently, by using 2-perf (Techniscope) pull-down. Most modern cinematographers use "2.40" to refer to anamorphic whilst "2.35" refers to a matted frame.
DVD video
A similar anamorphic technique is used to store video on DVD. DVDs using anamorphic widescreen make the most effective use of the available resolution, as well as allowing a film to automatically expand to fit widescreen television sets. Widescreen pictures on DVD are stored in a horizontally squeezed format, in order to maximize the available storage space, and not waste as much on storing the black letterboxing bars. Sources that are close to 16:9 are transferred to DVD taking up the entire 16:9 frame. Sources that are wider than 16:9, such as 2.35:1 video is transferred to DVD with black bars, although the title is still flagged for 16:9 playback, and the bars are not as pronounced as they would be for 4:3 playback.
When a DVD is inserted into a player, the player will do one of two things depending on the type of television set in use: If the DVD player is set up to output a widescreen image, the player will signal to the TV that the video is anamorphic, and then sends the video, still horizontally squeezed, to the television, which will stretch it horizontally to fill the screen. The combination of this squeeze-and-stretch restores the video back to its original widescreen aspect ratio, minimizing the loss of quality. If the DVD player is setup to output a letterboxed picture, the DVD player stretches the picture horizontally to restore the correct aspect ratio, and adds letterbox-style "black-bars" before sending the signal to the TV.
This technique is not used on all DVD discs; some use the standard letterboxing technique. Those that do use the anamorphic technique typically specify "anamorphic widescreen", "enhanced for 16x9", "enhanced for widescreen televisions" or a similar statement on the packaging, though there is currently no widely accepted standard for such labeling. If a DVD claims to be widescreen, but does not have a label like one of the previous, it may use the standard letterbox technique, resulting in decreased resolution for widescreen pictures. Some DVD packaging explicitly mentions that the lower-quality letterbox technique is used; when viewing such a letterboxed DVD on a widescreen display, it may be necessary to zoom in on the picture in order to utilize the full width of the screen.
External links
- The Ultimate Guide to Anamorphic Widescreen DVD (for Dummies!) (http://www.thedigitalbits.com/articles/anamorphic/)
- "Of Apertures and Aspect Ratios", Widescreen Museum (http://www.widescreenmuseum.com/widescreen/apertures.htm)