PART 1 The Foundations of Television Production Although there are a number of different HD standards, the currently most popular are 720p, 1080i, and 1080p. All of these individual formats are compatible around the world. They are not limited to specific countries as are NTSC, PAL, and SECAM. THE TELEVISION PICTURE There are times when television engineers may seem to be obsessed with "picture quality"-- with color fidelity, definition, tonal gradation, gamma, and so on. The reason that the image quality of the pictures we produce is so important is that it--just like the accompanying sound--directly affects the viewer's enjoyment of the production. If a camera's picture is not sufficiently sharp, the viewer will not be able to see detail or texture clearly. If color varies from one camera to the next, changes will distract the viewer when cutting between the shots. If tones are not reproduced successfully, subtle variations will be lost, and surfaces will appear to be flat and unmodeled. Clearly, picture quality matters, but how good can a television picture be? Initially, it depends on the system used. At best, it can be superb. But there are inevitably various losses between the camera lens and the home screen that degrade the picture. Picture Detail All video systems have a maximum limit to the amount of detail they can convey. In television, the definition (resolution) is initially influenced by the number of picture lines the system uses. But it is also affected by system design. As the image of the scene is scanned into the camera, the video should ideally be able to change in strength to correspond with tonal dif- ferences. The faster it can change, the finer the detail that it can resolve. This rate of change is measured as frequency. 46 Apart from these technical parameters, many other factors can affect picture clarity, including the lens performance. It may be dirty or badly focused. Lighting may produce lens flares. The glass of a prompter attached to the camera can degrade picture quality. Or the viewer may be watching a poor video recording. There can be many reasons for low-quality images! Picture Tones Although it is not immediately obvious in most pictures, the range of tones that a television system can normally reproduce is quite restricted compared with those in the original scene. Our eyes appear to detect subtle tonal differences over a remarkably wide range--even when the lightest areas are as much as a thousand times brighter than the darkest (a 1000:1 contrast range). This impression, however, is largely due to the human brain's adaptation--that is, its ability to readjust instantaneously to the brightness of localized areas that we are looking at. Image reproduction systems have considerably less accommodation. Color negative film, for example, can handle a contrast range of only about 100:1 (10 stops) and still reproduce subtle half tones in between. If the subject contrast is greater than this range, it will result in tonal gradation and details being lost in the highlights and/or shadows. Most electronic sensor cameras can easily handle a 40:1 range. Home television receivers are more likely to be limited to a range of around 20:1. Any picture tones that exceed this range (e.g., bright highlights, deep shadows) will appear as detail-free white or black areas on the screen. If the television receiver itself has not been adjusted for optimum contrast/brightness, or light is falling on its screen and diluting darker tones, reproduced picture quality can be considerably impaired. Many televisions display little more than a 10:1 or 15:1 range. Whether such limitations matter in practice depends on how important tonal subtlety is in your shot. If a map that you are showing reproduces as a blank sheet because lighter tones have been blocked off, it is embarrassing! On the other hand, if dark clothing lacks subtle