Interactive Television (iTV) A service that may be enabled with DTV which allows viewers to participate or access more information about the program. The interactivity may be implemented by selecting different TV channels (unknown to the viewer) or by a return control path to the service provider. Besides using a phone line, DVB has devised return control paths for satellite (DVB-RCS), cable (DVB-RCC) and terrestrial (DVB-RCT). Some consider interactivity is the future of television – the ‘killer app(lication)’ that will make DTV a commercial success. Others talk of lean back (viewing) and lean forward (interaction) being very different attitudes of both body and mind and question whether the two belong in the same place. See also: Return control.
Inter-frame (compression)
Compression which involves more than one frame. Inter-frame compression compares consecutive frames to remove common elements and arrive at ‘difference’ information to describe frames between I-frames. MPEG-2 and MPEG-4 use two types of inter-frame processed pictures – the ‘P’ (predictive) and ‘B’ (bi-directional) frames. As ‘P’ and ‘B’ frames are not complete in themselves but relate to other adjacent frames, they cannot be edited independently. See also: Cut edit, MPEG-2, MPEG-4
Interlace Factor The reduction in vertical definition during vertical image movement due to interlaced (rather than progressive) scans. Experimentally it is found to be about 30%. Note that, when scanning film frame-per-frame (i.e. 24 or 25fps – not 3:2 pull-down to 60fps), or a succession of electronic frames each representing a single snapshot in time, there is no vertical movement between fields and the Interlace Factor has no effect. See also: 24PsF
Interlace (scan)
Method of scanning lines down a screen (vertical refresh) – as used in most of today’s television broadcasts and originally designed to suit the needs of CRT displays and analog broadcasts. Interlace is indicated in television scan formats by an ‘I’ e.g. 1080I, etc. Each displayed picture comprises two interlaced fields: field two fills in between the lines of field one. One field displays odd lines, then the other shows even lines. For analog systems, this is the reason for having odd numbers of lines in a TV frame e.g. 525 and 625, so that each of the two fields contain a half-line, causing the constant vertical scan to place the lines of one field between those of the other. The technique greatly improves the portrayal of motion and reduces picture flicker without having to increase the picture rate, and therefore the bandwidth or data rate. Disadvantages are that it reduces vertical definition of moving images by about 30% (see Interlace Factor) of the progressive scan definition and tends to cause some horizontal picture detail to ‘dither’ – causing a constant liveliness even in still pictures. Interlaced video requires extra care for processing, such as in DVE picture size changes, as any movement between fields has to be detected if the higher-quality frame-based processing is used. Also frame freezes and slow motion need ‘de-interlace’ processing. There is continuing debate about the use of interlaced and progressive scans for DTV formats. This has intensified now that the increasingly popular panel displays are all progressive. See also: Interlace Factor, Progressive
Internegative As a part of the chemical lab film intermediate process internegatives are created by contact printing from interpositives. These very much resemble the cut negative. The stock is the same as for interpositives: slow,
very fine grain with a gamma of 1, and the developed film is orange- based. To increase numbers, several internegatives are copied from each interpositive. These are then delivered to production labs for large scale manufacture of release prints. See also: Film basics (Tutorial 2)
Interocular distance (Stereoscopic)
The distance between the centers of the lenses of two recording cameras. A typical distance would be 63.5 mm (approximating average adult eye spacing). The term ‘interaxial’ is sometimes also used interchangeably with ‘interocular’ (when referring to eyesight, ‘interpupillary’ is often used).
Interoperability The ability of systems to interoperate – to understand and work with information passed from one to another. Applied to digital media this means video, audio and metadata from one system can be used directly by another. Digital signals may be originated in various formats and subjected to different types of compression so care is needed to maintain interoperability.
Interpositive This is a first part of the chemical lab intermediate process where a positive print of film is produced from the cut (edited) camera negative. Interpositives are made by contact printing onto another orange-base stock. In order to preserve as much detail as possible from the negative, including its dynamic range, interpositive material is very fine grain, slow and has a gamma of 1. During the copying process, grading controls are used to position the image density in the center of the interpositive material’s linear range. As a part of the process of going from one camera negative to, possibly, thousands of prints, a number of interpositives are copied from the negative. See also: Film basics (Tutorial 2)
Interpolation (spatial)
Defining the value of a new pixel from those of its near neighbors. When re-positioning or re-sizing a digital image, for dramatic effect or to change picture format, more, less or different pixels are required from those in the original image. Simply replicating or removing pixels causes unwanted artifacts. For far better results the new pixels have to be interpolated – calculated by making suitably weighted averages of adjacent input pixels – to produce a more transparent result. The quality of the results will depend on the techniques used (bi-cubic is generally accepted as being good) and the number of pixels (points) taken into account (hence 16-point interpolation), or area of original picture, used to calculate the result. See also: Anti-aliasing, Interpolation (temporal), Sub-pixel
Interpolation (temporal)
Interpolation between the same point in space (pixel) on successive frames. It can be used to provide motion smoothing and is extensively used in standards converters to reduce the judder caused by field rate changes – such as between 50 and 60 Hz. The technique can also be adapted to create frame averaging for special effects and slow motion. Various qualities of processing are used. It can be very complex, attempting to work out how each element in successive pictures is moving in order to synthesis ‘between’ images.
Intra-frame (compression)
Compression that occurs within one frame. The compression process only removes redundant and visually less significant information from within the frame itself. No account is taken of other frames. JPEG and the ‘I’ frames
A B C D E F G H I J
K L
M N O P Q R S T U V
73
W X Y Z
GLOSSARY OF TERMS
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99