Decibel (dB)

Units of measurement expressing ratios of power that use logarithmic scales to give results related to human aural or visual perception. Many different attributes are given to a reference point termed 0 dB – for example a standard level of sound or power with subsequent measurements then being relative to that reference. Many performance levels are quoted in dB – for example signal to noise ratio (S/N). Decibels are given by the expression: 10 log10 P1/P2 where power levels 1 and 2 could be audio, video or any other appropriate values.

Defragmentation See Fragmentation

Deliverables Material that is delivered for use by customers – TV channels, agencies, Web, DVD, mobile phones, etc. The business of making deliverables has expanded with the widening of the scope of digital media. Today it is a considerable business in its own right. Traditionally deliverables have been made as copies from an edited master of programs and commercials. This process involves replaying the master and recording onto the customers’ required storage format D5, DVCPRO, HDCAM, etc. It may also involve other treatments such as pan and scan, color grading and standards conversion from say HD 1920 x 1080/60I to SD 720 x 625/50I. If going to mobile phones that have smaller screens with different aspect ratios and supplied by relatively low bandwidth links, then the treatments such as conversion to a lower frame rate, image re-framing and further removal of image detail may be used. The 1080/24P or 25 HD format can be used to make high quality versions for any television format, and even for film. This top-down approach preserves quality as the HD image size means any resizing will be downward, making big pictures smaller, rather than up-res’d blow-ups from smaller pictures. For frame rate conversion, over half a century of running movies on TV has established straightforward ways to fast play 24 f/s material to at 25 f/s and to map it to 60 Hz vertical rates using 3:2 pull-down for television.

For film output, a popular image size is 2K. This is only very slightly wider than 1080-line HD (2048 against 1920 pixels per line), and, for digital exhibition, the same 1080 lines is used. But that material may need further editing, for example, a commercial for showing in a different country may require a new soundtrack and text for pricing. There may be censorship issues so shots need adjusting or replacing. Also the growth of digital media platforms means that more work may be required for a wider deliverables market – with escalating numbers of versions required. Some scenes of a digital film master may need re-grading for domestic TV viewing or further processing to fit the bandwidth and screen limitations of mobile viewing. This type of work may be best undertaken with the finished program in uncommitted form, where the source material and all the tools and their settings are available, so that any part of the program can be re-accessed, changed and the whole program re-output exactly as required for the target medium and without compromising the quality of other deliverables. See also: 3:2 Pull-down, ARC, Down-res, Up-res

Densitometer

An instrument used to measure the density of film, usually over small areas of images. The instrument actually operates by measuring the light passing through the film. When measuring movie film density, two sets of color

DiBEG

Digital Broadcasting Experts Group, founded September 1997 to drive the growth of digital broadcasting and international contribution by promoting

filters are used to measure Status M density for camera negative and intermediate stocks (orange/yellow-based) and Status A for print film to correctly align with the sensiometric requirements of the stocks.

Density

The density (D) of a film is expressed as the log of opacity (O). D = Log10 O Using a logarithmic expression is convenient as film opacity has a very wide range and the human sense of brightness is also logarithmic. See also: Film basics.

Depth grading (Stereoscopic)

A post production process where negative and positive parallax convergence are adjusted. This is not only a creative tool used to place objects on the Z axis but also a way to ensure that stereoscopic content can be comfortably watched on the screen size it is intended for. For example, in a post suite the director may be viewing a film on a small projection screen but the final delivery format may be a large theatre or IMAX. In practice the eyes have little ability to diverge (up to one degree is considered the rule of thumb) and this is especially a consideration in depth grading for very large screens with positive parallax images, where the distance between the left and right representations of an image may be very widely spaced. Sometimes the term Depth Budget is used to refer to the combined value of positive and negative parallax and expressed as a percentage of screen width. See also: Parallax

DFS

Distributed File System – used to build a hierarchical view of multiple file servers and shared files on a network. Instead of having to think of a specific machine name for each set of files, users only need to remember one name as the key to a list of shared files on multiple servers. DFS can route a client to the closest available file server and can also be installed on a cluster for even better performance and reliability. Medium-to-large sized organizations are most likely to benefit from using DFS while smaller ones should be fine with ordinary file servers.

DI See Digital intermediate

Diagnostics Tests to check the correct operation of hardware and software. As digital systems continue to become more complex, built-in automated testing becomes an essential part of the equipment for tests during both manufacture and operation. This involves some extra hardware and software to make the tests operate. Digital systems with such provisions can often be quickly assessed by a trained service engineer, so speeding repair. Remote diagnostics can make use of an Internet connection to monitor and test a product at the customer’s site while working from a central service base. Thus expert attention can be used immediately on site. Interdependent multiple systems, such as a video server and its clients, may require simultaneous diagnostics of all major equipment. Here, combining data links from a number of pieces of networked equipment effectively extends the Remote Diagnostics to larger and more complex situations. See also: Diagnostics

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GLOSSARY OF TERMS