Category Archives: R

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 can be 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.

Soft RAID
A RAID system implemented by low level software in the host system instead of a dedicated RAID controller. While saving on hardware, operation consumes some of the host’s power.

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. When RAM chips first arrived they had a huge impact and, as they have grown in capacity and speed while unit price remains reasonably stable, their applications and importance have multiplied.

DRAM – Dynamic RAM. DRAM chips provide high density memories which must be powered and clocked to retain data. DRAM offers very speedy access to data and is vital for the fast computer performance and there is a large industry dedicated to the development and manufacture of ever faster and bigger DRAM chips. Synchronous DRAM (SDRAM) is faster and DRAM, and now DDR SDRAM (Double Data Rate) technology is increasing the performance of many of the newer PC and graphics products. Currently DDR3 clocking at 100 MHz can achieve data transfer rates of 6400 MB/s and allows storage capacity of 8 Gb per chip. DDR4 is on the way. Along with these performance breakthroughs power consumption is being reduced.

There are many more variations and versions of RAM to suit specific applications.

SRAM – Static RAM memory chips in general behave like dynamic RAM (DRAM) except that static RAMs retain data in a six-transistor cell only needing power to operate (DRAMs require clocks as well). Because of this, current available capacity is lower than DRAM – and costs are higher, but speed is also greater. SRAM is becoming increasingly popular as an alternative to hard disk drives in computers to achieve faster operation.

See also: Flash Memory

Raw data (a.k.a. source data)

Data that has not been processed for use. It is often written as ‘RAW’, which may make you think it is an acronym. It is not.

Raw data usually applies to the output of digital cinematography cameras that can generally deliver images that include the full brightness range that its imager can extract from a scene. The data has not been tampered with, not processed for color or to suit any target viewing conditions, such as cinema or gamma corrected for home TV viewing. The raw data is as the imager saw it with debayering applied where needed.

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 480) 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, 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. Like a chain, it is only as good as its weakest link.

For decades television was only available in one analogue resolution in any one country. That improved with digital standard definition services (SDTV). Then HD at 1080 x 1920, with four-times the picture area, doubled the horizontal and vertical resolution. More recently 4K UHD doubles HD with 2160 x 3840 sized images. 8K UHD doubles those figures again.

See also: Concatenation, MTF, Viewing distance

Resolution co-existence

Term coined by Quantel to describe equipment able to operate with several moving image formats at the same time. For example, an editing system able to store and operate with any DTV production format material, making transitions between shots, composing layers originating from more than one format (resolution) and outputting in any chosen format.

Good equipment will be designed for fast operation at the largest specified TV format, e.g. 4K (3840 x 2160 UHD), and so may operate faster with smaller images, but also may be able to handle larger images.

See also: Resolution independent

Resolution independent

A term to describe 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 and UHD has encouraged new equipment able to operate with many, or all, of the video standards.

In today’s converged media world the gamut of digital ‘video’ formats now includes motion picture formats up to 4K and mobile TV operating in many formats down to 320×240, or 176×144 on some phones.

By their nature computers can handle files of almost any size so, when used for images, they can be termed ‘resolution independent’. However, as larger images require more processing, more storage and more bandwidth so, for a given platform, the speed of operation will slow as the resolution increases.

Other considerations when changing between video image resolutions may include the need to reformat or partition disks, check for sufficient RAM, allow extra time for RAM/disk caching and to select an appropriate display.

See also: Resolution co-existence

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 the result 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. Typically 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. DVB includes methods for return paths for cable, DVB-RCC; satellite-RCS; and terrestrial–RCT, services. While cable and terrestrial are devised to operate economically for individual viewers, the satellite solution is more appropriate for head-ends or groups – due to cost. Interestingly DVB-RCS has been adopted by many companies operating in the general telecoms world.

See also: WiMax

RGB

The abbreviation for the Red, Green and Blue signals, the primary colors of television. Cameras 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 depend on 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, relatively quick and easy. This has led to many new designs and looks appearing on television as well as 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 wide range of equipment including, mixers, lighting, 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 yet available.

Run-length encoding

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.