• refers to the shape of a film or video image, specifically the ratio of image width to image height. When referring to a filmed image, aspect ratio is typically denoted in decimal form as a ratio of units width per unit height, e.g. 1.33:1 or 1.78:1. In video, this is usually expressed in whole number dimensions such as 4x3 or 16x9
  

• refers to the type of video signal output by a video camera, telecine, editing system or tape deck for recording, broadcast or display on a monitor. Non-HD broadcast video signals (collectively known as Standard Definition or SD) conform to the NTSC standard in the US, whereas European countries utilize the PAL and SECAM standards. All of these standards produce a picture with an aspect ratio of 4x3 or 1.33:1. The HDTV standard was developed to be a single, international standard and has a 16x9 or 1.78:1 aspect ratio.

• refers to the film gauge and type of gate used in a film camera, dictating the maximum available area upon which an image can be recorded. For professional motion picture cameras, the four primary formats in use today are 35mm, Super35, 16mm and Super16. Within a given format one can record images in a wide variety of aspect ratios according to the needs of the production and creative sensibilities of the director and cinematographer.
  

• The Super35 and Super16 formats record on standard 35mm and 16mm film but utilize a specially enlarged and recentered gate to make use of space originally reserved for an optical soundtrack, increasing the available image area to provide a higher-resolution image with less visible film grain. Not all cameras and lenses are compatible with the super formats, but, all other things being equal, shooting in a super format will produce a better image than its regular counterpart.
  
  




• A Ground Glass is a piece of glass or fiber-optic material etched with framelines to define the shooting aspect ratio(s) in a film camera. This does not limit the area of the film negative upon which the image is recorded but instead designates which part of the total recorded image is to be extracted for exhibition. The framelines on a ground glass are not themselves recorded to the film but rather are used to communicate to the laboratory which part of the negative is to be transferred to video via telecine or printed to film for projection. Once the desired aspect ratio for a production has been decided, the production company must inform the camera rental company of its choice so that the proper ground glass can be installed in the company’s cameras prior to commencing production. Because the choice of aspect ratio can profoundly affect the entire production and postproduction workflow, it is very important that the production company clearly communicate its choice of ground glass to the camera rental company when placing a camera order.
  
  
  Arri and Aaton Super35 TV 1.33:1 Ground Glasses
  
  
• A ground glass with two or more aspect ratios inscribed on it is known as a Combination or “Combo” Ground Glass. Because of incompatibilities between certain aspect ratios and manufacturing constraints, some combinations of aspect ratios are not available in a combination ground glass. Camera rental companies can typically provide a list of the combination ground glasses they carry, as well as recommend which combinations will work well for a given set of required end deliverables.
  
• Letterboxing, Sidebarring and Pan-and-Scan are the three primary methods used to resize images acquired in one aspect ratio for display in another ratio. Letterboxing converts an image acquired in a widescreen aspect ratio (e.g. 1.85:1 or HDTV 1.78:1) for display on a device with a narrower aspect ratio (like TV 1.33:1) by shrinking the overall image size to accommodate the complete image width and adding black bars on the top and bottom of the screen to make up for the loss in vertical image size. Sidebarring works the same way, but in reverse: an image with a narrow aspect ratio is centered within a widescreen display with black bars on the sides. Pan-and-scan selects a (typically) 1.33:1 extraction of the widescreen image to be displayed and discards the rest.
  

I. Production for HD Delivery
So you’re planning a production – let’s say a commercial spot – and you want to be able to broadcast it in HDTV. How does this influence your production process? Does that mean you have to shoot with an HD video camera? Absolutely not. Shooting in HD can offer some advantages depending on the specifics of your production, but to take full advantage of the improved resolution and color fidelity of HDTV the origination medium of choice for maximum picture quality remains film. Most telecine facilities today have the ability to output HD video from a scanned film negative to a variety of tape and digital storage media, from which point the postproduction workflow for HD-originated and film-originated media is the same. On the production end, shooting film for HDTV delivery is in most ways identical to shooting film for NTSC broadcast, though there are a few subtle (and important) differences. Perhaps the most significant of these is the aspect ratio.


II. The HDTV Aspect Ratio
HDTV has an aspect ratio of 1.78:1, which was chosen as a compromise between the 1.85:1 and 1.66:1 aspect ratios used for theatrical feature film projection in the US and Europe respectively. The 1.78:1 aspect ratio allows content originally produced in these theatrical aspect ratios to more exactly fit the HDTV screen without the letterboxing or image cropping needed to fit them on a 1.33:1 standard definition television set, thereby preserving the original composition of the image while eliminating the distracting black bars and avoiding resolution loss. Research by the engineers at NHK (the Japan Broadcasting Corporation) during the development of the HDTV standard found a substantial correlation between a larger viewing angle and the perceived “realness” of an image as experienced by the viewer. Simply put, an image that occupied a larger proportion of the viewer’s field of view was better able to engage that viewer. Because human vision has a greater horizontal field of view than its vertical field of view, for any given screen area a widescreen image offers a greater perception of immersion than a square one. Improved resolution and color rendering aside, the widescreen aspect ratio of the HDTV standard offers a more immersive experience for the viewer than previous video standards.


III. HDTV 1.78:1 Image Area in Regular and Super Formats
Shooting film for HDTV delivery exclusively is, at its most basic, no more complicated than ordering an HDTV 1.78:1 ground glass with your camera package. Because regular 35mm and 16mm film frames have a 1.33:1 aspect ratio, however, shooting in the HDTV 1.78:1 aspect ratio in regular 35mm or regular 16mm makes rather inefficient use of the available image area. In absolute numeric terms, the TV 1.33:1 aspect ratio in regular 35mm utilizes 66% of the format’s maximum image area with HDTV 1.78:1 utilizing 54%. HDTV 1.78:1 would utilize so small a percentage of the already-small regular 16mm frame that no such ground glass has been made. Super35 and Super16 offer far superior 70% and 86% utilizations respectively thanks to the more rectangular aspect ratio of the super formats. Given this disparity, when shooting HDTV 1.78:1 it makes a great deal of sense to “go Super” and take advantage of the substantial gains in resolution and grain reduction afforded by the greater image area.


IV. Hybrid Production for HDTV 1.78:1 and TV 1.33:1
While shooting film exclusively for HDTV broadcast is relatively simple as outlined above, this process is somewhat complicated by the fact that very seldom is an HD master the only required deliverable at the end of a production. While market penetration of HDTV-capable televisions has grown rapidly over the past three years and continues to accelerate, by the end of 2005 it is still projected that only 22% of television-owning US households will own an HDTV-capable television (as quoted by Peter Wilson of High Definition & Digital Cinema Ltd. at IBC 2005). The remaining 78% will still require broadcasts in standard definition NTSC, which means that content producers will still need to deliver NTSC versions of their HDTV-formatted media.

While it is possible to downconvert HD video signals to NTSC using a variety of video processing systems, the difference in aspect ratio between the two standards always results in some compromise of image integrity in addition to the loss of resolution and color depth due to the conversion. This disparity of aspect ratio is usually resolved by one of two methods: letterboxing or pan-and-scan. Letterboxing of an HDTV 1.78:1 image for TV 1.33:1 NTSC delivery has the advantage of preserving the entire original composition of the image, but results in a smaller image overall and black bars on the top and bottom of the screen. Pan-and-scan delivers an image that fills the entire 1.33:1 screen, but does so by discarding part of the original 1.78:1 image. If done without the supervision of the director or cinematographer, this can result in the omission of important details from the frame and a less pleasing overall composition. Shooting 1.33:1 for HDTV delivery is generally considered inadvisable since many 1.78:1 HDTV displays will automatically resize 1.33:1 images to fill their full screen area, horizontally stretching the image in a manner rather unflattering to human faces and equally distorting for graphics.


V. Combination Ground Glasses for HDTV 1.78:1
The most effective and least compromising method of resolving aspect ratio differences between the NTSC and HDTV standards is to acquire images composed for both aspect ratios simultaneously during actual production, a solution made possible by the use of a combination ground glass. By incorporating frame lines for both TV 1.33:1 and HDTV 1.78:1 aspect ratios, a TV 1.33:1/HDTV 1.78:1 combination ground glass allows the cinematographer to actively frame the image for delivery on both video standards without any compromise of image quality or composition.

Available in both regular and super formats, TV 1.33:1/HDTV 1.78:1 combination ground glasses can be ordered in a variety of configurations including common center, common top, and TV reduction (with the TV 1.33:1 frame shrunk to fit inside the HDTV 1.78:1 framelines such that the two aspect ratios share the same top and bottom) to suit the preferences of the director and cinematographer. Not all camera rental companies stock every possible configuration, but most can special order ground glasses to meet their clients’ requirements if given sufficient advance notice. When in doubt, call the camera rental company regarding ground glass availability well in advance of commencing production to ensure that your needs can be accommodated.

Common HDTV 1.78:1 / TV 1.33:1 aspect ratio combinations in 35mm and Super35

Article and Illustrations © Schumacher Camera 2005