RAID Redundant Array of Independent Disks. A grouping of standard disk drives together with a RAID controller to create storage that acts as one disk to provide performance beyond that available from individual drives. Primarily designed for operation with computers, RAIDs can offer very high capacities, fast data transfer rates and much increased reliability of data. The latter is achieved through disk redundancy so that disk errors or failures can be detected and corrected. A series of RAID configurations is defined by levels and, being designed by computer people, they start counting from zero. Different levels are suited to different applications.
RAID levels
Level 0 No redundancy - benefits only of speed and capacity - generated by combining a number of disks.
Level 1 Complete mirror system - two sets of disks both reading and writing the same data. This has the benefits of level 0 plus the security of full redundancy - but at twice the cost. Some performance advantage can be gained in read because only one copy need be read, so two reads can be occurring simultaneously.
Level 2 An array of nine disks. Each byte is recorded with one bit on each of eight disks and a parity bit recorded to the ninth. This level is rarely, if ever, used.
Level 3 An array of n+1 disks recording 512 byte sectors on each of the n disks to create n x 512 'super sectors' + 1 x 512 parity sector on the additional disk which is used to check the data. The minimum unit of transfer is a whole superblock. This is most suitable for systems in which large amounts of sequential data are transferred - such as for audio and video. For these it is the most efficient RAID level since it is never necessary to read/ modify/ write the parity block. It is less suitable for database types of access in which small amounts of data need to be transferred at random.
Level 4 As level 3 but individual blocks can be transferred. When data is written it is necessary to read the old data and parity blocks before writing the new data as well as the updated parity block, which reduces performance.
Level 5 As level 4, but the role of the parity disk is rotated for each block. In level 4 the parity disk receives excessive load for writes and no load for reads. In level 5 the load is balanced across the disks.
RAM Random access memory - cost-effective memory chips (integrated circuits) used extensively in computers to give fast access (compared to disks, tapes etc. - RAM has no moving parts) and very high data rates. RAM is available in several different forms and has been subjected to Moore's Law for over three decades of digital 'video' formats now includes motion picture formats up to 4K and mobile TV operating in many formats down to 320x240, or 176x144 on phones. See also: Resolution co-existence
Raw data (a.k.a. source data) Data that has not been processed for use. Digital cinematography cameras can generally output raw data of images that includes the full brightness range it can extract from a scene, and a signal that has not been processed for color or to suit any target viewing conditions - such as cinema or gamma corrected for home TV viewing.
Resolution A measure of the finest detail that can be seen, or resolved, in a reproduced image. Whilst it is influenced by the number of pixels in the display (e.g. high definition 1920 x 1080, broadcast SDTV 720 x 576 or 720 x 487) note that the pixel numbers do not define the resolution but merely the resolution of that part of the equipment chain. The quality of lenses, picture displays, film processes, edit systems and film scanners, etc., in fact any element in the program stream (from scene to screen), must be taken into account in assessing overall system resolution. See also: Concatenation, MTF R
Resolution independent A term used to describe the notion of equipment that can operate at more than one resolution, though not necessarily at the same time. Historically, most dedicated television equipment was designed to operate at a single resolution although some equipment, especially that using the ITU-R BT.601 standard, could switch between the specific formats and aspect ratios of 525/60 and 625/50. More recently, the advent of the multiple formats of HDTV has encouraged new equipment able to operate with many, or all, of the video standards. In today's converged media world the gamut
Resolving power The resolving power of an imaging medium is a measure of its maximum spatial resolution. For digital media the pixel count dictates the maximum possible resolving power. For film it is assessed by exposing it to special test images comprising sine wave bars of successively higher frequencies. The results on the processed film are then judged by a panel of viewers - making them somewhat subjective. See also: MTF
Restoration Hiding or removing the defects acquired by old (archive) material and content. Digital technology has enabled many new and easy-to-use procedures to provide fast and affordable restoration. These range from fully automated systems - that depend on recognizing generic faults and treating them - to hands-on operations that offer access to appropriate toolsets - often presented as 'brushes'. These have been applied to both television and to film, and succeeded in making available many old archives for the ever-hungry TV channels.
Return control (path) Return control is needed for interactive television. It needs only to offer quite a low data rate but have little latency, as action should be followed as soon as possible by reaction. See also: WiMax
RGB The abbreviation for the Red, Green and Blue signals, the primary colors of television. Cameras and telecines have red, green and blue receptors, the TV screen has red, green and blue phosphors or LEDs. RGB is digitized with 4:4:4 sampling which generates 50% more data than 4:2:2.
Rotoscoping The practice of using frames of live footage as reference for painting animated sequences. Today, the meaning has extended to cover a whole range of manual retouching techniques. While the painting will always be down to the skill of the artist, modern graphics equipment integrated with a video disk or RAM store makes rotoscoping, or any graphical treatment of video frames, quick and easy. This has led to many new designs and looks appearing on television as well as the more mundane practices such as image repair.
RS 232 A standard for serial data communications defined by EIA standard RS- 232 that is designed for short distances only - up to 10 meters. It uses single-ended signaling with a conductor per channel plus a common ground, which is relatively cheap, easy to arrange but susceptible to interference - hence the distance limitation.
RS 422 Not to be confused with 4:2:2 sampling or 422P MPEG, this is a standard for serial data communications defined by EIA standard RS-422. It uses current-loop, balanced signaling with a twisted pair of conductors per channel, two pairs for bi-directional operation. It is more costly than RS232 but has a high level of immunity to interference and can operate over reasonably long distances - up to 300m/1000 ft. RS 422 is widely used for control links around production and post areas for a range of equipment - VTRs, mixers, etc.
RSN Real Soon Now. A phrase coined by Jerry Pournelle to satirize the tendency in the computer industry to discuss (and even offer for sale) things that are not actually available yet. See also: Vaporware
Run-length coding A system for compressing data. The principle is to store a pixel value along with a message detailing the number of adjacent pixels with that same value. This gives a very efficient way of storing large areas of flat color and text but is not so efficient with pictures from a camera, where the random nature of the information, including noise, may actually mean that more data is produced than was needed for the original picture.