A television standard defines the way in which different information, such as image and sound data, is transmitted from the transmitter to the receiver during television transmission . It makes sense to distinguish between three different levels of transmission:
- Definition of the picture and sound parameters
- Electrical signal transmission in baseband : either as analog video and audio signals or digitally coded
- Remote transmission: analog or digital RF - modulation types
History of the television standard
Similar to the worldwide expansion of radio , there was also a need for international regulation for television. With television, however, much more had to be determined than just bandwidth , station spacing and the broadcast frequencies to be allocated , because radio stations only transmitted sounds. When television broadcasting comes to sound , the image signal added.
Almost at the same time as the development of black and white television , there were also experiments with color television . In the first attempts several variants were developed. For example, television pioneer John Logie Baird tried a two-color system for his mechanical television . Others experimented either with three channels (in each channel a partial image was transmitted in one of the three primary colors) or the transmission via one channel and synchronized rotating color filters in front of the camera and receiver. Here, however, a significantly higher number of individual images had to be transmitted in order to create the impression of a flicker-free image. The American television station CBS introduced a color television system with rapidly rotating color filters in 1943.
In these early attempts at CBS color television, images were transmitted using the transmission standard of 405 lines and 144 frames per second. The picture was very good, but the color receivers with the color filter discs, for example, were very clunky, loud and incompatible with the system with 525 lines and 60 fields per second, which had been introduced in the meantime, due to these much larger discs in front of the small screen. In 1941, the US Federal Communications Commission (FCC) introduced its first black and white standard with a 525 line image and a sound-to-image interval of 4.5 MHz. (see also → National Television Systems Committee )
In Germany in 1935, with the introduction of television, 180 lines at 25 full frames per second were used as the norm, but only one year later they were replaced by 441 lines with 50 fields. When television was first introduced in Great Britain, experiments were initially carried out with 240 lines with 25 frames and 405 lines with 50 fields (broadcast on a weekly basis). There, too, a decision was made after only one year for the standard with 405 lines, later called "Standard A". In France, television was officially introduced with 453 lines, during the German occupation of France the standard was changed to 441 lines and temporarily retained even after the end of the war, temporarily in parallel with the new 819 line standard.
Post war norms
France introduced a new broadcast standard in 1948 with 819 lines per picture.
In September 1948, a 34-person group of experts in West Germany decided on a future broadcast standard under the direction of the technical director of the NWDR Werner Nestel, a line standard of 625 lines with a 2: 1 interlaced procedure and a picture structure frequency of 50 Hz, that means: 25 times per second, a successive film image is electronically broken down into 625 lines, whereby in the odd 50ths of a second only the lines with the odd line numbers 1, 3, 5, etc. of the respective image and in the even 50ths of a second then the lines with the even line numbers 2, 4, 6 etc., i.e. 2 * 25 = 50 fields per second, are transmitted. The two fields of an image are put together or interlocked exactly to form a full image on the screen (see animation below). These parameters resulted on the one hand from the traditional frequency of the mains alternating current in Europe of 50 Hz; on the other hand, the specification of 625 lines corresponded to an approximate conversion of the US American standard NTSC to these established European technical conditions: 30 images 525 lines result in a total of 15,750 to be formed Lines per second. 25 frames x 625 lines correspond to 15625 lines per second. The line frequency is 15,625 Hz. This proposed standard was then dealt with by the responsible committee CCIR ( Comité Consultatif International des Radiocommunications ) of the Geneva International Telecommunication Union (ITU) as the basis for a uniform western and southern European television broadcasting standard.
In 1961 this was then declared in Stockholm with certain changes (in particular the definition of the channel bandwidth at 7 MHz and a spacing of the audio and video carrier frequency of 5.5 MHz) as the official standard proposal, the so-called "Gerber standard" of the CCIR ( named after the chairman of the CCIR working group Walter Gerber ). In contrast, some Central European countries (such as the GDR up to 1956/57) and the majority of Eastern European countries used the frequency bands extended to 8 MHz and a sound / video carrier spacing of 6.5 MHz, although like the CCIR standard, a number of lines of 625. It is known as the OIRT standard . Some of the OIRT countries switched to the CCIR standard in the 21st century .
Analog television standards
In the early days of television (1930s to 1950s) broadcasting was only in black and white. During this time, the technical standards in different countries were already diverging. During the Second World War , many countries interrupted their television activities and some of them switched to a different standard when they resumed.
The standards still in use after this phase of change were designated by the ITU with Roman numerals and currently with capital letters and classified as follows:
|Norm code||Lines||Frame rate
|Sound / picture distance
|J||525||30th||+4.50||6.00||4.2||0.75||negative||FM||UHF / VHF||NTSC|
|525||30th||+4.50||3.58||6.00||4.2||0.75||negative||FM||UHF / VHF||NTSC|
|625||25th||+4.50||3.58||6.00||4.2||0.75||negative||FM||UHF / VHF||PAL|
Terminology and parameters
Examples of a combined designation from the ITU specifications with the capital letter codes for black and white standards and for a color television system used and applied are as follows:
- PAL J = PAL system with black and white standard J
- NTSC M = NTSC system with black and white standard M.
- Secam L = Secam system with black and white standard L
The most important parameters are the number of lines , image changes per second , image / sound spacing, sound modulation ( FM or AM ) and polarity of the image modulation (positive or negative). The remaining columns relate to the special bandwidth that a TV channel requires to transmit the audio and video signals in the spectrum .
All these TV-standards common to the interlaced ( interlaced ), d. H. each frame is transmitted in two successive fields, so that double the field frequency results.
Channel grid VHF
- System B: E-2… E-12 (CCIR except F, Monaco , Italy )
- System M: A-2… A-13 (FCC)
- System D: RI… R XII (OIRT)
- System A: B-1… B-14 (UK old)
- System I: IB, ID, IF, IH, IJ ( Ireland )
- System F: F-2, F-4… F-12, F-8 A (F)
- System B: A, B, C, D, E, F, G, H, H1 (Italy)
- System B ': 4… 10 ( Morocco )
- System B ": 0… 11, 5 A ( Australia )
- System B: 1… 9 (NZ)
- System M: J-1… J-12 ( Japan )
Channel grid UHF
- System G: E-21… E-72 (not FCC)
- System M: A-14… A-83 (FCC)
- System M: J-45… J-62 (Japan)
The color TV was added later, for the United States and Japan in the 1950s and for the rest of the world in the 1960s or later. Since it was to remain downwardly compatible with black and white television , the existing standards were retained and only a color signal was added in the form of an auxiliary carrier for coloring.
Black-and-white receivers cannot decode this additional carrier and therefore receive color transmissions as usual in black-and-white; this is how compatibility is established. Color receivers decode black and white and color signals and generate the color image from the two together. This procedure is common to all terrestrial analog standards.
The added color signal can be modulated in three different ways: PAL , SECAM or NTSC. In principle, any of the three color standards can be combined with any of the black and white standards A – N. In reality, however, PAL and SECAM are mostly used with one of the 625/25 standards and NTSC only with standard M. However, there are also “hybrids” such as B. PAL on Norm M in Brazil .
RF transmission (analog)
Antenna-specific parameters that are necessary to capture the signal, such as antenna direction, polarization, antenna location, are not taken into account in this consideration.
With classic terrestrial transmission, the parameters are:
- Video carrier frequency (there are fixed channel rasters for each standard, even if this is no longer relevant for modern receivers due to the continuous tunability),
- The size of the larger and the smaller collateral ligament and the position of the larger collateral ligament,
- Positive or negative modulation, black and white level,
- Distance and direction of the sound carrier,
- Modulation of the sound carrier ( AM or FM ), pre-emphasis used in FM
- various two-channel sound processes for the transmission of several audio channels.
Cable uses exactly the same parameters as classic terrestrial transmission. However, other frequencies are permitted that are reserved for non-television purposes in classic terrestrial transmission; these lie
- between Volume II and Volume III : lower special canal area ,
- between band III and 300 MHz: upper special channel area,
- between 300 MHz and band IV: extended special channel range, also called hyperband .
In classic, analog satellite transmission, the parameters are:
- Center frequency FM carrier,
- Nominal stroke,
- Video pre-emphasis,
- Stroke limitation,
- Distance between the sound carriers,
- Modulation of the sound carrier (FM or QPSK with ADR ), preemphasis used with FM.
RF transmission (digital)
- The modulation used is OFDM with QPSK, 16QAM or 64QAM on each individual carrier.
- DVB-H (mobile devices)
- The modulation used is also OFDM.
- DVB-T2 (not compatible)
- Different types of quadrature amplitude modulation are used (16QAM, 64QAM or 256QAM), depending on the required robustness.
- A COFDM method with quadrature amplitude modulation is used on each individual carrier (16QAM to 4096QAM). DVB-C2 is currently of almost no importance in practice (as of 2019), since the transmission of HDTV channels is already possible with the previous DVB-C standard.
Signal transmission in baseband (analog)
In the case of analog transmission in the baseband, the following image parameters are added:
- Color modulation ( PAL , NTSC , SECAM )
- Color carrier frequency (3.58 ... MHz: NTSC-3.58, 4.43 ... MHz: PAL-4.43 and NTSC-4.43, 4.25 and 4.406 ... MHz: SECAM)
- Size of the horizontal blanking interval (12 of 64 µs)
- Size of the vertical blanking interval (24.5 ... 25 lines for CCIR, 19.5 ... 22.5 for FCC)
Signal transmission in baseband (digital)
MPEG-2 (H.262) or MPEG-4 (H.264, H.265) is used for digital transmission of the picture (rarely also MPEG-1), for sound both MPEG-1 and MPEG-2 audio ( Layer 2 or AAC) as well as Dolby Digital (AC-3 or E-AC3) are used, whereby MPEG audio is mandatory. However, there are usually restrictions:
- certain image formats
- maximum data rate
- GOP length
- temporal image-sound offset
The following parameters are then the actual image parameters:
- Frame rate
- Use interlaced or progressive scan
- Number of lines
- Location of the primary colors in CIElab - color space
- Gamma value for the assignment between value and brightness
- With analog transmission: horizontal resolution
- With digital transmission: horizontal number of pixels
- Pixel geometry or ratio of image height and image width
Often in the digital sector, “PAL” is used as an abbreviation for “625 lines / 25 image changes per second with PAL color carrier” and “NTSC” as an abbreviation for “525 lines / 30 image changes per second with NTSC color carrier”. This is wrong, however, because component signals are used almost exclusively in digital technology, and the exact specification of a country's TV standard is black-and-white standard + color standard. So use z. B. the USA the standard M with NTSC, most of Western Europe standard B / G with PAL, the former GDR standard B / G with SECAM, most of Eastern Europe standard D / K with SECAM or PAL, France standard L with SECAM. Many former SECAM countries have now migrated to PAL, but generally retain the underlying black-and-white standard.
Furthermore, there are different standards for analog television
- Stereo sound : A2 , NICAM , MTS
- Text services: Teletext , Antiope , Closed Captioning
- Compatible widescreen transmission: PALplus
- PALplus : an extension of PAL, downward compatible
- D2-MAC : brought about a quality improvement primarily through separate ( time-division multiplexed ) transmission of the image signal, the color signal and the digital audio signal, was mainly transmitted via satellite, could not prevail.
- HDTV : Collective term for television standards with higher resolutions
- DVB : Digital Video Broadcasting, collective term for various digital television standards
The digital television standards are based on some characteristics of the analog television standards, such as the number of lines and frame rate. The MPEG-2 standard is generally used to compress the data .
In contrast to analog television standards, the number of columns in a picture is another feature of digital television standards. Together with the number of image lines, the so-called image resolution in image points (pixels) is obtained. The number of columns is ideally chosen so that the height of the individual pixels does not differ significantly from their width in the image display. Instead of the traditional 4: 3 aspect ratio, 16: 9 is being used more and more because of the changed display devices (flat screen TVs and video projectors) .
- Charles Poynton: Digital Video and HDTV Algorithms and Interfaces , Morgan Kaufmann Publishers, 2003. ISBN 1-55860-792-7
- Author collective Werner and Barth, television repair practice. VEB Verlag technology. Berlin, 1962.