digital fact book, Apuntes de Comunicación Audiovisual

¡Descarga digital fact book y más Apuntes en PDF de Comunicación Audiovisual solo en Docsity!

The Digital Fact Book

Converged media

20th anniversary edition

Acknowledgements Mark Horton, Lenny Lipton, Steve Owen, Phil Streather, Dave Throup, Roger Thornton Quantel R&D for their co-operation and many contributions and to the many contributors and commentators from the industry around the world

Copyright Quantel Limited 1988, 1989, 1990, 1991, 1992, 1994, 1996, 1998, 2000, 2002, 2003, 2008

The Digital Fact Book

20th Anniversary Edition Converged Media

A reference manual for the television broadcast & post production industries includes stereoscopic 3D

Editor: Bob Pank

Index

Quantel and digital technology p

Introduction to the 20th anniversary edition p

Abbreviations p

TV standards descriptions p

Digital terms p

Tutorial 1 – Into digits p

Tutorial 2 – Film basics p

White paper – Stereoscopic 3D post p

Standards on-line p

Some general browsing p

Directory p

Quantel contacts and addresses p

This document is viewable as a standard PDF. However, it has been optimized for viewing in Adobe Acrobat 6.0 or later. Bookmarks have been included for added functionality, and can be found by clicking View > Navigation Panels/Tabs > Bookmarks. ‘See also’ references that have been included beneath entries can be clicked to view the associated information.

Quantel and digital technology

In 1973, the company now known as Quantel developed the first practical analog to digital converter for television applications. That innovation not only gave Quantel its name (QUANtized TELevision), it also started a process that has fundamentally changed the look of television, the way it is produced and delivered. Quantel’s contribution to the changes leading to the digital age is best traced through its products, which have extended to film and print as well as television.

1975 Quantel demonstrates the DFS 3000 , the world’s first digital framestore synchronizer. TV coverage of the 1976 Montreal Olympic games is transformed with synchronized shots from an airship ‘blimp’ freely used and quarter-sized picture inserts mark the genesis of digital effects.

1977 The first portable digital standards converter, the DSC 4002 heralds high quality and easily available conversion.

1978 DPE 5000 series, the first commercially successful digital effects machine, popularizes digital video effects.

1980 The DLS 6000 series introduces digital still storage for on-air presentation. The new DFS 1751 framestore synchronizer is just one rack unit in height.

1981 The revolutionary Paintbox®^ creates the market for video graphics

• and, thanks to continuous development, continues as the industry standard.

1982 Mirage introduces the TV page turn and is the first digital effects machine able to manipulate 3D images in 3D space.

1986 Harry®^ makes multi-layering of live video a practical proposition and introduces nonlinear operation and random access to video clips.

1988 Quantel publishes the first edition of the Digital Fact Book.

1989 V-Series , the second generation Paintbox, is faster, smaller and more powerful than its ‘classic’ predecessor.

1990 The Picturebox®^ stills store integrates the storage, presentation and management of stills. Harriet® , the dynamic graphics workstation manipulates still graphics over live video.

2003 QColor – powerful in-context color correction option for iQ and eQ is introduced, integrating colorcorrection into the heart of the mainstream post production process.

2005 Newsbox – a complete news system in a box, combining ingest, editing, playout and control within a single system that can be up and running within hours of unpacking. Quantel also introduced a novel approach to HD post production with its ‘Pay as you Go HD’ option for eQ – designed to give post houses and broadcasters a ‘soft start’ in HD production.

Pablo – complete color correction combining image-processing hardware with color correction software for quality, performance and interactivity for in-context color grading.

2006 Pablo HD – provides cost-effective Pablo power for HD and SD.

Marco – standalone desktop editing software with the Quantel editing interface that runs on a standard PC. Newsbox – complete self-contained news system available in ‘HD now’ and ‘HD upgradeable’ configurations.

Revolver – secondary color correction in Pablo without using keys. Colorists can work intuitively on multiple levels within a picture to produce natural looking results.

2007 Genetic Engineering – a teamworking infrastructure for post and DI enabling different suites to work on the same clips at the same time with no compromises.

Stereoscopic 3D – tools for efficient handling of 3D shot material in post.

For the latest developments please contact Quantel or visit our website www.quantel.com

The team researching and writing the first edition of the Digital Fact Book back in 1987, when digital technology represented but occasional islands in the analog sea in which we all swam, could not possibly have imagined what our industry would look like today. Back then, digital was going to make the world so simple – fixing all our problems and making our lives easy.

But no one could have expected the explosion of choice that digital would bring, nor the unbelievable opportunities that have been brought about by new media channels, the internet and the mighty computer. This kind of explosion – perpetually driven yet further forward at breakneck speed by an endless stream of digital innovation – is exactly why we still need a Digital Fact Book. Today it’s all about digital content for the whole universe – a world where the knowledge and skills of the traditional ‘broadcasting’ community has cemented a fruitful union with the new wave of ‘all media’ IT-based professionals. The result is a truly converged digital world – which is why this edition has ‘converged media’ as its subheading.

So what will the next 20 years bring? The team that put this edition together has absolutely no idea – but my goodness we know it’s going to be good and we’re looking forward to it! What is certain is that we will continue to track its unfolding with further editions of the Digital Fact Book.

We hope you find the new edition a useful source of reference in this exciting converged world. As ever, we welcome any comments or additions – email us at [email protected].

Bob Pank

Introduction to the 20th anniversary edition

TV standards descriptions

TV standards are written in many different ways. The method used in this book is shown below and follows how they appear in ITU-R BT 709: i.e. –

Number of pixels per line x number of lines per frame/vertical refresh rate (in Hz) progressive or interlaced (P or I). For example:

1920 x 1080/50I

Notes:

1. The vertical refresh rate shown for interlaced scans is twice the whole frame rate (two interlaced fields make up one whole frame). This assumes that interlace is only ever 2:1 (theoretically it can be greater but never is for broadcast purposes). So 1920 x 1080 50I has 25 whole frames per second.

2. Digital standards are usually quoted for the active lines and pixels only – so no blanking space is included

Examples: Digital SDTV in Europe 720 x 576/50I (analog equivalent is 625/50I that includes 49 lines of blanking)

An HD standard in USA 1920 x 1080/30P

Brief format Lines per frame/vertical refresh rate, progressive or interlaced e.g.: 1080/30P

See: Dual Link

The nominal 30 frames/60 fields per second of NTSC color television is usually multiplied by 1000/1001 (= 0.999) to produce slightly reduced rates of 29.97 and 59.94 Hz. This offset gives rise to niceties such as drop-frame timecode (dropping one frame per thousand – 33.3 seconds) and audio that also has to run at the right rate. Although having strictly analog origins from the very beginning of NTSC transmissions as a fix-it to avoid a clash of frequencies, it has also been extended into the digital and HD world where 24 Hz becomes 23.97 and 30 frames/60 fields per second are again changed to 29. and 59.94 Hz. Of course, as the frame/field frequency changes, so do the line and color subcarrier frequency as all are locked together. Note that this does not apply to PAL color systems as these always use the nominal values (25 Hz frame rate).

The reason for the 1000/1001 offset is based in monochrome legacy. Back in 1953, the NTSC color subcarrier was specified to be half an odd multiple (455) of line frequency to minimize the visibility of the subcarrier on the picture. Then, to minimize the beats between this and the sound carrier, the latter was to be half an even multiple of line frequency, and to ensure compatibility with the millions of existing monochrome TV sets, the sound carrier was kept unchanged – at 4.5 MHz – close to 286 times the line frequency (Fl). Then, in a real tail-wags-dog episode, it was decided to make this exactly 286 times... by slightly altering the line frequency of the color system (and hence that of the color subcarrier and frame rate). Interestingly it is said that the problem could soon have been solved with a little improved engineering, so avoiding the need for this awkward frequency offset and all the many thousands of hours of additional engineering and operational effort this has caused down the years.

Here’s the math.

Fl = frames per second x number of lines per frame Nominally this is 30 x 525 = 15,750 kHz But it was decided that: 286 x Fl = 4.5 MHz So Fl = 4,500,000/286 = 15,734.265 kHz This reduced Fl by 15734.265/15750 = 1000/1001 or 0.

As all frequencies in the color system have to be in proportion to each other, this has made:

NTSC subcarrier (Fl x 455/2) = 3.579 MHz 30 Hz frame rate (Fl/number of lines per frame) = 29.97 Hz

Digital terms

13.5 MHz

This is the sampling frequency of luminance in SD digital television. It is represented by the 4 in 4:2:2. The use of the number 4 is pure nostalgia as 13.5 MHz is in the region of 14.3 MHz, the sampling rate of 4 x NTSC color subcarrier (3.58 MHz), used at the very genesis of digital television equipment.

Reasons for the choice of 13.5 MHz belong to politics, physics and legacy. Politically it had to be global and work for both 525/60 (NTSC) and 625/50 (PAL) systems. The physics is the easy part; it had to be significantly above the Nyquist frequency so that the highest luminance frequency, 5.5 MHz for 625-line PAL systems, could be faithfully reproduced from the sampled digits – i.e. sampling in excess of 11 MHz - but not so high as to produce unnecessary, wasteful amounts of data. Some math is required to understand the legacy.

The sampling frequency had to produce a static pattern on both 525 and 625-line standards, otherwise it would be very complicated to handle and, possibly, restrictive in use. In other words, the frequency must be a whole multiple of the lines speeds of both standards.

The line frequency of the 625/50 system is simply 625 x 25 = 15,625 Hz

(NB 50 fields/s makes 25 frames/s)

So line length is 1/15,625 = 0.000064 or 64μs

The line frequency of the 525/60 NTSC system is complicated by the need to offset it by a factor of 1000/1001 to avoid interference when transmitted. The line frequency is 525 x 30 x 1000/1001 = 15,734.265 Hz. This makes line length 1/15,734.265 = 63.5555μs

The difference between the two line lengths is 64 – 63.55555 = 0.4444μs

This time divides into 64μs exactly 144 times, and into 63.5555μs exactly 143 times. This means the lowest common frequency that would create a static pattern on both standards is 1/0.4444 MHz, or 2.25 MHz.

Now, back to the physics. The sampling frequency has to be well above 11 MHz, so 11.25 MHz (5 x 2.25) is not enough. 6 x 2.25 gives the sampling frequency that has been adopted – 13.5 MHz.

Similar arguments have been applied to the derivation of sampling for HD. Here 74.25 MHz (33 x 2.25) is used.

See: 4:1:1, 4:2:0, 4:2:2, 4:4:4, 4fsc, Nyquist (frequency)

A picture aspect ratio that has been used as a preferred way to present 16:9 images on 4: screens. It avoids showing larger areas of black above and below letterboxed pictures but does include more of the 16:9 image than 4:3. It is commonly used for analog transmissions that are derived from 16:9 digital services.

Picture aspect ratio used for HDTV and some SDTV (usually digital).

See also: 14:9, 4:3, Widescreen

24P

Refers to 24 frames-per-second, progressive scan. 24 f/s has been the frame rate of motion picture film since talkies arrived. It is also one of the rates allowed for transmission in the DVB and ATSC digital television standards – so they can handle film without needing any frame-rate change (3:2 pull-down for 60 fields/s ‘NTSC’ systems or running film fast, at 25f/s, for 50 Hz ‘PAL’ systems). 24P is now accepted as a part of television production formats – usually associated with high definition 1080 lines to give a ‘filmic’ look on 60 Hz TV systems.

A major attraction is a relatively easy path from this to all major television formats as well as offering direct electronic support for motion picture film and D-cinema. However, the relatively slow refresh rate has drawbacks. For display it needs to be double shuttered – showing each frame twice to avoid excessive flicker, as in cinema film projection, and fast pans and movements are not well portrayed. Faster vertical refresh rates are preferred for sports and live action.

See also: 24PsF, 25P, 3:2 Pull-down, ATSC, Common Image Format, DVB, Versioning

24PsF (segmented frame) A system for recording 24P images in which each image is segmented – recorded as odd lines followed by even lines. Unlike normal television, the odd and even lines are from an image that represents the same snapshot in time. It is analogous to the scanning of film for television. This way the signal is more compatible (than normal progressive) for use with video systems, e.g. VTRs, SDTI or HD-SDI connections, mixers/switchers etc., which may also handle interlaced scans. Also it can easily be viewed without the need to process the pictures to reduce 24-frame flicker.

See also: Interlace Factor, Progressive

25P

Refers to 25 f/s, progressive scan. Despite the international appeal of 24P, 25P is widely used for HD productions in Europe and other countries using 50 Hz TV systems. This is a direct follow-on from the practice of shooting film for television at 25 f/s.

See also: 24P, 24PsF, Common Image Format, DVB

2K

See Film formats

3D (stereo)

In television, film or cinema, 3D may refer to material that is shot using a set of ‘stereo’ cameras and shown on the screen as a pair of superimposed stereo images (usually ‘decoded’ by the viewer with polarized spectacles). Also known as stereo3D and stereoscopic 3D.

See also: Stereoscopy

3G SDI

See: Serial Digital Interface

This is a set of sampling frequencies in the ratio 4:1:1, used to digitize the luminance and color difference components (Y, R-Y, B-Y) of a video signal. The 4 represents 13.5 MHz, (74.25 MHz at HD) the sampling frequency of Y, and the 1s each 3.75 MHz (18.5625) for R-Y and B-Y (ie R-Y and B-Y are each sampled once for every four samples of Y).

With the color information sampled at half the rate of the 4:2:2 system, this is used as a more economic form of sampling where video data rates need to be reduced. Both luminance and color difference are still sampled on every line but the latter has half the horizontal resolution of 4:2:2 while the vertical resolution of the color information is maintained. 4:1:1 sampling is used in DVCPRO (625 and 525 formats), DVCAM (525/NTSC) and others.

See also: 4:2:0, 4:2:2, DV (DVCAM and DVCPRO)

Raster line

Pixels • • • • • • • • • Y Y Y Y Y Y Y Y Y Cr Cr Cr Cb Cb Cb

A sampling system used to digitize the luminance and color difference components (Y, R-Y, B-Y) of a video signal. The 4 represents the 13.5 MHz (74.25 MHz at HD) sampling frequency of Y while the R-Y and B-Y are sampled at 6.75 MHz (37.125 MHz) – effectively on every other line only (ie one line is sampled at 4:0:0, luminance only, and the next at 4:2:2).

This is used in some 625-line systems where video data rate needs to be reduced. It decreases the overall data by 25 percent against 4:2:2 sampling and the color information has a reasonably even resolution in both the vertical and horizontal directions. 4:2:0 is widely used in MPEG-2 coding meaning that the broadcast and DVD digital video seen at home is usually sampled this way. 625 DV and DVCAM coding also use 4:2:0. However the different H and V chroma bandwiths make it inappropriate for post applications.

See also: 4:1:1, 4:2:2, DV (DVCAM), MPEG-

A ratio of sampling frequencies used to digitize the luminance and color difference components (Y, R-Y, B-Y) of an image signal.The term 4:2:2denotes that forevery foursamples of the Y luminance, there are two samples each of R-Y and B-Y, giving less chrominance (color) bandwidth in relation to luminance. This compares with 4:4:4 sampling where full same bandwidth is given to all three channels – in this case usually sampled as RGB.

The term 4:2:2 originated from the ITU-R BT.601 digital video sampling where 4:2:2 sampling is the standard for digital studio equipment. The terms ‘4:2:2’ and ‘601’ are commonly (but technically incorrectly) used synonymously in TV. For SD the sampling frequency of Y is 13.5 MHz and that of R-Y and B-Y is each 6.75 MHz, providing a maximum color bandwidth of 3.37 MHz – enough for high quality chroma keying. For HD the sampling rates are 5. times greater, 74.25 MHz for Y, and 37.125 MHz for R-Y and B-Y.

The origin of the term is steeped in digital history and should strictly only be used to describe a specific format of standard definition digital television sampling. However, it is widely used to describe the sampling frequency ratios of image components (Y, B-Y, R-Y) of HD, film and other image formats.

See also: 13.5 MHz, Co-sited sampling, Digital keying, ITU-R BT.601, ITU-R BT.709, Nyquist

This is the same as 4:2:2 but with the key signal (alpha channel) included as the fourth component, also sampled at 13.5 MHz (74.25 MHz at HD).

See also: Dual link

A

4K

See Film formats

5.1 Audio

See Discrete 5.1 Audio

50P and 60P

These indicate a video format that has 50 or 60 progressive frames per second and usually refers to high definition. The original digital television standards only included progressive frame rates above 30 Hz for image sizes up to 720 lines – thus limiting the total video data. More recently this has been expanded up to 60 Hz for the larger 1080-line television standards to provide the best of the best – the maximum HD image size with a fast rate for rendition of fast action and progressive frames for optimum vertical resolution (better than interlaced scans). The baseband signal produces twice the data rates of the equivalent interlaced (50I and 60I) formats, pushing up equipment specifications. See also: SDI (3G SDI)

See ITU-R BT.

See ITU-R BT.

See Discrete 5.1 Audio

8 VSB/16 VSB

See VSB

AAC

Advanced Audio Coding, a codec originally known as MPEG-2 NBC (non-backwards compatible), is considered the successor to MP3, with about 25 percent efficiency improvement. However this performance has more recently been considerably enhanced with aacPlus , also known as High Efficiency AAC (HE-AAC), and included in MPEG- and delivers CD quality stereo at 48 kb/s and 5.1 surround sound at 128 kb/s.

Websites: (AAC) www.audiocoding.com, (aacPlus) www.codingtechnologies.com

A

AAF

The Advanced Authoring Format – an industry initiative, launched in 1998, to create a file interchange standard for the easy sharing of media data and metadata among digital production tools and content creation applications, regardless of platform. It includes EBU/SMPTE metadata and management of pluggable effects and codecs. It allows open connections between equipment where video, audio and metadata, including information on how the content is composed, where it came from, etc., are transferred. It can fulfill the role of an all-embracing EDL or offer the basis for a media archive that any AAF-enabled system can use. Quantel products make extensive use of AAF.

In 2007 AAF Association, Inc. changed its name to Advanced Media Workflow Association (AMWA), with the tag ‘Putting AAF and MXF to work’, with direction and focus on file-based workflows including AAF, MXF and other formats. It is involved with the MXF Mastering Format Project that aims to provide real-world solutions for key workflows, focusing on creating a single MXF master file from which multiple versions of a program may be created.

Website: www.aafassociation.org

AC-

See Dolby Digital

Accommodation (Stereoscopic)

The ability of our eyes to refocus at a new point of interest.

In normal vision, the processes of focusing on objects at different distances (accommodation) and convergence/divergence (the angle between the lines of sight of our eyes) are linked by muscle reflex. A change in one creates a complementary change in the other. However, watching a stereoscopic film or TV program requires the viewer to break the link between these different processes by accommodating at a fixed distance (the screen) while dynamically varying eye convergence and divergence (something we don’t do in life and can quickly lead to headaches if over-used in stereo3D) to view objects at different stereoscopic distances.

Active line

The part of a television line that actually includes picture information. This is usually over 80 percent of the total line time. The remainder of the time was reserved for scans to reset to the start of the next line in camera tubes and CRT screens. Although the imaging and display technologies have moved on to chips and panels, there remains a break (blanking) in the sampling of digital TV as in ITU-R BT.601 and ITU-R BT 709. These ‘spaces’ carry data forthe start of lines and pictures, as well as otherinformation such as embedded audio tracks.

See also: Active picture