Category Archives: 0-9

1.125 MHz

This is a common frequency that can be derived from 625/50 PAL (and 525/60 NTSC) that runs through SD, HD and UHD digital television standards using 4:4:4 or 4:2:2 sampling, including 1080-line HD and UHD at 25, 30, 60 Hz frame rates. It can be created from the old analog (PAL or NTSC) black-and-burst signal. Because 1.125 MHz is a common frequency, black and burst was widely used as a timing reference signal in the early days of HD.

See also: 13.5, Tri-level sync

10-bit lin

A type of digital sampling of analog images that creates 10-bit (210, 1024 possible levels) numbers to describe the analog brightness levels of an image. Lin, short for ‘linear’ means the levels are assigned evenly to the levels of the analog signal they describe. So an LSB change describes the same change in level if it is in a bright area or a dark area of the picture. Most professional HD and some SD television is sampled this way according to ITU-R BT.601 and 709. 10-bit lin sampling allows good quality to be maintained through TV production and post production where the processes can make particular demands outside the range of normal viewing, and so produces good results for viewers. However if color grading is required then the wide dynamic range that can be described by 10-bit log would be more useful, or indeed one of the newer high dynamic range formats.

See also: 10-bit log, Gamma, Color Space

10-bit log

This usually refers to a 10-bit sampling system that maps analog values logarithmically rather than linearly. It is widely used when scanning film images which are themselves a logarithmic representation of the film’s exposure. This form of sampling is available directly from some digital cinematography cameras.

The 10-bit data can describe 210 or 1024 discrete numbers, or levels: 0 – 1023 for each of the red, blue and green (RGB) planes of an image. However, as all electronic light sensors have a linear response and so produce an output directly proportional to the light they see, when scanning film they represent the transmittance of the film. Usually it is negative film that is scanned and this means a large portion of the numbers generated describe the scene’s black and dark areas (representing bright areas of the original scene), and too few are left for the light areas (dark scene) where ‘banding’ could be a problem – especially after digital processing such as grading and color correction. Transforming the numbers into log (by use of a LUT) gives a better distribution of the digital detail between dark and light areas and so offers good rendition over the whole brightness range without having to use more bits. A minimum of 13-bit linear sampling converted to 10-bit log sampling means sufficient detail in the pictures is stored to allow headroom for downstream grading that is common in film production.

10-bit log is the basis for sampling in the Cineon and SMPTE DPX formats that are still widely used in the post production and DI industries.

See also: 10-bit lin, LUT

1000/1001

Historically 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 in step with the video. Although having strictly analog origins, dating from the very beginning of NTSC color transmissions in 1953 as a fix-it to avoid a clash of frequencies, the 1000/1001 offset has been extended into the digital, HD and UHD world where 24 Hz becomes 23.976 and 30 frames/60 fields per second are again changed to 29.97 and 59.94 Hz. Of course, as the frame/field frequency changes, so do the line and color subcarrier frequency as they all have to be 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 0.999

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

Following on, all digital sampling locked to video is affected so, for example, nominal 48 and 44.1 kHz embedded audio sampling becomes 47.952 and 44.056 kHz respectively.

As the reasons for ‘drop-frame’ were analog, it is not a requirement of digital television but still the frequencies appear in digital TV standards, and they are widely used, even though analog TV transmissions are now switched off in most countries.

See also: Drop-frame timecode, Embedded audio

13.5 MHz

This is the sampling frequency of luminance in SD digital television systems as defined by the ITU. 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 to 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 line frequencies 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 its offset 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 adopting sampling frequency for luminance of 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 for luminance sampling.

See also: 1.125 MHz4:1:1, 4:2:0, 4:2:2, 4:4:4, 4fsc, Nyquist (frequency)

14:9

A picture aspect ratio that has been used to present 16:9 images on 4:3 screens. It avoids showing larger areas of black above and below letterboxed pictures but does include more of the 16:9 image than displaying at 4:3. As the population of 16:9 TV screens increases and 4:3 declines, so the use of 14:9 continues to diminish.

2.25 MHz

This is a common frequency that can be derived from 625/50 PAL (and 525/60 NTSC) that runs through SD, HD and UHD digital television standards. It can be created from the old analog black and burst signal. 2.25 MHz, or multiples thereof, runs through all the major digital television standards. These can be locked to black and burst. They include 1080-line HD at 25, 30 fps.

See also: 13.5, Tri-level sync

2:2 F1/F2

A film frame being transported as 2:2 (pSF) is placed into two consecutive video fields. F1/F2 denotes that the film frame is carried in field one and the following field two. This is commonly referred to “normal dominance” or “perfect cadence”.

See also pSF

2:2 F2/F1

A film frame being transported as 2:2 (psf) is placed into two consecutive video fields. F2/F1 denotes that the film frame is carried in a field two and the following field one. This is commonly referred to “reverse dominance” or “reverse cadence”.

See also pSF

24P

Refers to 24 frames-per-second, progressive scan. 24 f/s has been the frame rate of motion-picture film since the ‘talkies’ arrived. It is also one of the frame 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 f/s ‘NTSC’ systems or running film fast, at 25f/s, for 50 Hz ‘PAL’ systems). 24P is now accepted as a television production format – usually associated with high definition 1080 lines to give a ‘filmic’ look on 60 Hz TV systems. Drop-frame frequencies (e.g. 23.976Hz frame rate) may be used in in North America and other previously ‘NTSC’ countries).

A major attraction of 24P is its 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 frame-refresh rate has drawbacks. For display it needs to be double shuttered – showing each frame twice to avoid excessive flicker, as in cinema projection, and fast pans and movements are not well portrayed. Faster vertical refresh rates are generally preferred for sports and live action.

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

3:2 Pull-down (a.k.a. 2:3 Pull-down)

A method used to map the 24 or 23.98 f/s of motion picture film onto 30 or 29.97 f/s (60 or 59/94 fields) television, so that one film frame occupies three TV fields, the next two, etc. It means the two fields of every other TV frame come from different film frames making operations such as rotoscoping impossible, and requiring care in editing. Quantel equipment can unravel the 3:2 sequence to allow clean frame-by-frame treatment and subsequently re-compose 3:2.

The 3:2 sequence repeats every 1/6th of a second, i.e. every five TV frames or four film frames, the latter identified as A-D. Only film frame A is fully on a TV frame and so exists at one timecode only, making it the only editable point of the video sequence.

Film-to-TV transfer

3-2pulldown

3:2 pull-down creates a field-based result in that every other frame contains frames comprising two different fields. This makes subsequent compression, which then has to be based on 60 fields/s, less efficient than working with 30 frames/s. This may affect delivery platforms from TV broadcast to DVDs.

3D (graphics)

Applied to graphics, this describes graphics objects that are created and shown as three-dimensional objects. As computer power has increased, so has the ability to cost-effectively produce more and more detailed 3D graphic results, as seen in feature length animations. For television presentation, live 3D computer graphics is now commonplace. The considerable computational power needed for this is generally supplied by GPUs.

3D (stereo)

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

See also: Stereoscopy

4:1:1

This describes 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. For SDTV the 4 represents 13.5 MHz (74.25 MHz for HDTV) sampling frequency of the Y (luminance) signal, and the 1’s are each 3.75 MHz for SD (18.5625 MHz for HD) for the R-Y and B-Y color difference signals (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 that may be used where smaller data rates are required. 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.

4-1-1

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

4:2:0

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 bandwidths make it inappropriate for post applications.

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

4:2:2

Refers to a ratio of sampling frequencies used to digitize the luminance (Y) and color difference components (R-Y, B-Y) of an image signal. The term 4:2:2 denotes that for every four samples of the Y luminance, there are two samples each of R-Y and B-Y color difference, allowing less chrominance (color) bandwidth in relation to luminance. This compares with 4:4:4 sampling where the same full 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 5.5 times greater, 74.25 MHz for Y, and 37.125 MHz for each of 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 (1080-line HD is 5.5x SD, so 22:12:12 would be appropriate) and many other image formats including UHD.

See also: 13.5 MHz, Co-sited sampling, Digital keying, ITU-R BT.601, ITU-R BT.709, ITU-R BT.2020, Nyquist

4:2:2:4

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

4:3

The aspect ratio of traditional PAL and NTSC television pictures, originally chosen to match the 35mm film format of the time. All broadcast television pictures were 4:3 until the introduction of high definition when a wider image was considered to be more absorbing for viewers. For display tube manufacturers the most efficient aspect ratio would be 1:1 (square) as this is inherently the strongest shape, uses less glass and weighs less. More glass is used in 16:9 tubes so they are more expensive to produce. Such restraints do not apply to today’s TV screens and monitors using LED and Plasma technology.

4:4:4

One of the sampling frequency ratios used to digitize the luminance and color difference components (Y, B-Y, R-Y) or, more usually, the RGB components of a video signal. It supports an equal number of samples for each of three components or as RGB 4:4:4. It is commonly used in standard computer platform-based equipment, and for the highest quality results in high-end post production as well as in the production of movies.
For movies, the images are kept in the RGB form all the way through the DI process to create the Digital Source Master (DSM) that can be used to produce a Digital Cinema Distribution Master (DCDM). For distribution the DCI recommends the use of X´Y´Z´ chromaticity which can be derived from RGB using a 3D LUT.

See also: 2K, 4K, DCI, Digital intermediate, Dual link, LUT, X´Y´Z´

4:4:4:4

As 4:4:4, except that the key (matte, or alpha channel) is included as a fourth component. All four components are sampled at the same rate.

See also: Dual link

4fsc

A sampling rate locked to four times the frequency of color subcarrier (fsc) of analog coded PAL or NTSC TV systems. It was used in D2 and D3 VTRs but it has long been superseded by component sampling systems such as ITR 601.

See also: Component Video

50P and 60P

These indicate a video format that has 50 or 60 progressive frames per second and usually refers to high definition 1920 x 1080 or higher resolutions. The original HD digital television standards only included progressive frame rates above 30 Hz for image sizes up to 720 lines. It was later extended to the larger 1920 x 1080 television standards to provide a fast frame refresh rate for the rendition of fast action and progressive frames for optimum vertical resolution (better than interlaced scans). The baseband signal produces twice the data rate of the equivalent interlaced (50I and 60I) formats, pushing up equipment specifications.

See also: SDI (3G 6G, 12G, SDI)

8P8C

Connector for the ubiquitous dual unshielded twisted pair (UTP) Cat 5 or Cat 6 Ethernet cable – A.K.A. RJ45. These are those extremely common connectors that, for instance, are used on the ends of the cable that plug between an internet modem and a computer. As the use of IT products proliferates in some areas of television such as program playout and services for the internet, so the use of Ethernet and 8P8C connectors grows. It could be said that they are the IT version of the still-widely-used BNC.

See also: 13.5, Tri-level sync