What does secam l search mean? Difference between PAL and NTSC formats


Chroma signal V SECAM standard transmitted in frequency modulation (FM), one color component in one television line, alternately. The previous signal is used as the missing lines R-Y or B-Y accordingly, receiving it from memory. So, when the transmitter transmits only the signal R-Y, serving to influence the red phosphors of one row, the memory drives the blue phosphors, transmitting to them the same color changes that were in the previous row when the signal was received B-Y. The storage duration is equal to the transmission time of one line. Consequently, in television with a 625-line decomposition, the storage duration is 64 μs.

In analog television receivers, memory is used to implement delay line. During the return stroke of the beam, after each line, double switching is performed to direct the incoming signal to the corresponding electron gun, and the signal leaving the delay line is directed to the electron gun, which directly received the forward signal during the transmission of the previous line. Since creating a delay line through which an electrical signal would pass is difficult due to the too long period of time - 64 μs, ultrasound is used instead of electrical signals. Signals with a frequency varying from zero to 1.5 MHz generate corresponding mechanical oscillations at the input of the delay line, which take 64 μs to pass through. They are then converted back into electrical signals. The first delay lines were a rod made of solid material, at the ends of which there were piezoelectric elements. The next generation of delay lines was made in the form of a rectangular plate, and piezoelectric elements were located at the corners. This made it possible to reduce the dimensions due to repeated reflection of vibrations from the edges of the rectangle. Electromechanical transformation is based on the phenomenon of piezoelectricity (the occurrence of vibrations in certain crystals, such as quartz or titanate, when changing electrical voltages are applied, and vice versa, the occurrence of electrical voltages when such crystals vibrate). That. in the delay line, a piezoelectric crystal is attached to each end of the steel rod. A crystal installed at the input converts electrical signals into mechanical vibrations. These oscillations propagate along the rod and after 64 μs reach the second piezoelectric crystal, where they generate electrical signals of the same shape as those applied to the input. Modern technology uses digital signal processing, which involves delaying the signal by storing it in the RAM of the signal processor.

Objectively, a color television image in the SECAM standard has half the vertical resolution of a monochrome image. Subjectively, due to the greater sensitivity of the eye to the brightness component, such deterioration is almost not noticeable in average pictures. The use of digital signal processing further mitigates this disadvantage.

The use of frequency modulation, alternating color signal transmission and the YDbDr color model is a distinctive feature of SECAM from other analogue television standards. The fact that in SECAM, unlike PAL and NTSC systems, color signals are transmitted alternately, modulating the subcarrier in frequency, allows the color background of the image to be preserved without changes due to phase or amplitude distortions.

According to comprehensive studies conducted in 1965–66 at OSCT-2 ( Experimental color television station) of both systems, when choosing the best one for its widespread implementation in the USSR, neither of the two systems showed decisive technical or economic advantages over the other. The advantage of the SECAM system was less sensitivity to distortion during transmission over long-distance lines and during video recording; The disadvantage is the complexity of the equipment when mixing signals.

SECAM versions

Several modifications of the SECAM standard are used around the world. The method of transmitting color difference signals is the same in all cases, including the so-called pre-emphasis, and they differ only in the method of encoding the monochrome video signal, audio encoding and spectrum width. In fact, the method of identifying color could also be different - since only one signal is transmitted in each line, the decoder must correctly determine which one. For this, a method similar to “flashes” in PAL and NTSC systems could be used - in the invisible part of the line, at the end of the blanking pulse, an unmodulated subcarrier was transmitted, in the case of SECAM, either 4.406 MHz or 4.25 MHz, based on the frequency value, and identification occurred. Another method is the transmission of specially modulated signals at the end of the vertical blanking pulse, where the subcarriers took the extreme possible values ​​across the line, which simplified identification, especially in conditions of interference. Currently, this method is either not used or is a backup method, for example, in Russia both signals are transmitted simultaneously, and in France only the first option. But initially the second option was the main one, and once upon a time in the USSR and the countries of northern Africa only it was used.

Currently, on-air broadcasting of television channels in Russia is carried out in the SÉCAM system, however, in cable broadcasting networks, the vast majority of analogue television channels, including those presented on the open air, are transmitted in the PAL system, which makes it impossible to view them on old Soviet televisions in color .

Backronyms

As a joke, it is customary to decipher the acronym SECAM as “System Essentially Contrary to American Method” (a system essentially opposite to the American one).

Notes

Standards television broadcasting
Analog
SECAM PAL NTSC
Multichannel audio BTSC (MTS) NICAM Zweiton (A2, IGR)
Additional signals Teletext Subtitles CGMS-A GCR PDC VBI VEIL VITC WSS XDS
Digital
HDTV DVB ATSC ISDB SBTVD
Multichannel audio AAC (5.1) MP2 (Musicam) PCM LPCM
Hidden signals Teletext Subtitles CPCM AFD EPG

Unlike the black-and-white image transmission standard, which was more or less uniform throughout the world (only the distance between the image and sound transmission frequencies differed), there are several color television standards. The main color television systems are SECAM, PAL, NTSC. System SECAM adopted in the countries of the former USSR, as well as in France. System PAL adopted in Western European countries, except France. System NTSC adopted on the American continent and in Japan. Standards PAL And SECAM were developed on the basis of a single standard for black-and-white images and with the ability to receive a new television signal on old televisions, therefore they are partially compatible with each other (the image scan and brightness are encoded in the same way, but the color balance is encoded differently). Standard NTSC was developed independently of the old standard. IN currently Refinement is underway, and in some countries the introduction of digital standards, the advantages of which are increased picture resolution, increased picture frequency, and also noise immunity of the signal. In Russia, the transition to digital broadcasting is planned for 2010.

NTSC standard

NTSC (National Television System Color) - the first color television system to find practical use. It was developed in the USA and already accepted for broadcasting in 1953, and currently broadcasting using this system is also carried out in Canada, most countries of Central and South America, Japan, South Korea and Taiwan. It was during its creation that the basic principles of color transmission in television were developed. This standard defines a method for encoding information into a composite video signal. According to standard NTSC, each video frame consists of 525 horizontal lines of screen along which an electron beam passes every 1/30 of a second. When drawing a frame, the electron beam makes two passes across the entire screen: first along the odd lines, and then along the even lines (interlacing). Supports 16 million different colors. New versions of the NTSC standard "Super NTSC" and "16 x 9" are currently being developed, which will be part of the MPEG standard and the DVD development standard

PAL standard

SECAM standard

System SECAM (SEquentiel Couleur A Memoire), like PAL, uses a 625-line screen image at 25 frames per second. This system was originally proposed in France back in 1954, but regular broadcasting, after lengthy modifications, began only in 1967 simultaneously in France and the USSR. Currently, it is also accepted in Eastern Europe, Monaco, Luxembourg, Iran, Iraq and some other countries. The main feature of the system is the alternate transmission of color-difference signals through a line with further restoration in the decoder by repeating lines. However, in contrast to PAL And NTSC frequency modulation of subcarriers is used. As a result, color tone and saturation do not depend on illumination, but color fringing appears at sharp transitions in brightness. Typically, after bright areas of the image, the border is blue, and after dark areas, yellow. In addition, as in the system PAL, vertical color clarity is halved.
Sources:
http://www.videodata.ru/palsecam.htm
http://ru.wikipedia.org/wiki/%D0%92%D0%B8%D0%B4%D0%B5%D0%BE

IEEE1394 interface

(FireWire, i-Link) is a high-speed serial bus designed for exchanging digital information between a computer and other electronic devices.

Various companies promote the standard under their own brands:

    Apple - FireWire

Story

    in 1986, members of the Microcomputer Standards Committee decided to combine the existing various options Serial Bus

    in 1992, Apple began developing the interface

    IEEE 1394 standard adopted in 1995

Advantages

    Digital interface - allows you to transfer data between digital devices without loss of information

    Small size - a thin cable replaces a pile of bulky wires

    Easy to use - no terminators, device IDs or pre-installation

    Hot pluggability - the ability to reconfigure the bus without turning off the computer

    Low cost for end users

    Various data transfer rates - 100, 200 and 400 Mbps (800, 1600 Mbps IEEE 1394b)

    Flexible topology - equality of devices, allowing various configurations (the ability to “communicate” devices without a computer)

    High speed - the ability to process multimedia signals in real time

    Open architecture - no need to use special software

    Availability of power directly on the bus (low-power devices can do without their own power supplies). Up to one and a half amperes and voltage from 8 to 40 volts.

    Connect up to 63 devices.

IEEE 1394 bus can be used with:

    Computers

    Audio and video multimedia devices

    Printers and scanners

    Hard drives, RAID arrays

    Digital video cameras and VCRs

IEEE 1394 Device Organization

IEEE 1394 devices are organized according to a 3-level scheme - Transaction, Link and Physical, corresponding to the three lower levels of the OSI model.

Transaction Layer - routing of data streams with support for an asynchronous write-read protocol.

Link Layer - forms data packets and ensures their delivery.

Physical Layer - conversion of digital information into analog for transmission and vice versa, control of the signal level on the bus, control of access to the bus.

Communication between the PCI bus and the Transaction Layer is carried out by the Bus Manager. It assigns the type of devices on the bus, numbers and types of logical channels, and detects errors.

Data is transmitted in frames with a length of 125 μs. Time slots for channels are placed in the frame. Both synchronous and asynchronous operating modes are possible. Each channel can occupy one or more time slots. To transmit data, the transmitter device asks for a synchronous channel of the required bandwidth. If the transmitted frame contains the required number of time slots for a given channel, an affirmative response is received and the channel is granted.

FireWire Specifications

IEEE 1394

At the end of 1995, IEEE adopted the standard under serial number 1394. In digital cameras Sony's IEEE 1394 interface appeared before the adoption of the standard and was called iLink.

The interface was initially positioned for transmitting video streams, but it also caught the fancy of external drive manufacturers, providing high throughput for modern high-speed drives. Today many motherboards, as well as almost everything modern models laptops support this interface.

Data transfer rates - 100, 200 and 400 Mbit/s, cable length up to 4.5 m.

IEEE 1394a

In 2000, the IEEE 1394a standard was approved. A number of improvements have been made to increase device compatibility.

A wait time of 1/3 second has been introduced for bus reset until the transient process of establishing a reliable connection or disconnection of the device is completed.

IEEE 1394b

In 2002, the IEEE 1394b standard appeared with new speeds: S800 - 800 Mbit/s and S1600 - 1600 Mbit/s. Also increases maximum length cable up to 50, 70 and when using high-quality fiber optic cables up to 100 meters.

The corresponding devices are designated FireWire 800 or FireWire 1600, depending on the maximum speed.

The cables and connectors used have changed. To achieve maximum speeds at maximum distances, the use of optics is provided, plastic for lengths up to 50 meters, and glass for lengths up to 100 meters.

Despite the change in connectors, the standards remained compatible, which can be achieved using adapters.

On December 12, 2007, the S3200 specification was introduced with a maximum speed of 3.2 Gbit/s.

IEEE 1394.1

In 2004, the IEEE 1394.1 standard was released. This standard was adopted to enable the construction of large-scale networks and dramatically increases the number of connected devices to a gigantic number of 64,449.

IEEE 1394c

Introduced in 2006, the 1394c standard allows the use of Cat 5e cable from Ethernet. It can be used in parallel with Gigabit Ethernet, that is, use two logical and mutually independent networks on one cable. The maximum declared length is 100 m, Maximum speed corresponds to S800 - 800 Mbit/s.

FireWire connectors

There are three types of connectors for FireWire:

    4pin (IEEE 1394a without power) is used on laptops and video cameras. Two wires for signal transmission (information) and two for reception.

    6pin (IEEE 1394a). Additionally two wires for power.

    9pin (IEEE 1394b). Additional wires for receiving and transmitting information.

Integration

Audio and video equipment (digital CD, MD, VideoCD and DVD players, digital STB and Digital VHS) can already be integrated with computers and thus controlled. From this equipment it is possible to create systems - simple connection devices to each other using a single cable. After this, using a personal computer acting as a controller, you can perform the following operations: record from a CD player to a mini-disc, store digital radio broadcasts received via STB, enter digital video to a personal computer for subsequent editing and editing. Of course, it remains possible to directly exchange data between audio and video equipment without using a computer or, conversely, exchange data between two computers without regard to audio or video, as in local networks based on traditional Ethernet technologies.

NEC recently announced the development of a chip designed to support hardware routing between two IEEE-1394-based networks and enable their interoperability in future IEEE-1394 broadband home multimedia networks. This dual-port chip also includes firmware that automatically configures the network and allows connections to other network devices, including mobile communications. Thus, the home network can be extended beyond the boundaries of a specific home for a distance of up to one kilometer. Meanwhile, Sony continues to develop the concept of a home network based on the IEEE-1394 standard, and intends to support developments with a practical focus by releasing even more capacious, high-speed, compact, low-power components for a wide range of applications and subsequent integration into system chipsets. Today Sony is showing off new consumer electronics that can form a home network using i.Link. All this architecture bears the proud name Home Audio/Video Interoperability (HAVi)). It seems that thanks to the efforts of Sony, we will soon really live, if not in a digital house, then at least in a digital apartment. However, the IEEE-1394 standard, which is increasingly attracting the attention of not only manufacturers of audio and video devices, but also developers of equipment for personal computers, will no doubt soon become a new network standard ushering in the coming digital era.

In the operating system released in the fall of 2000 Microsoft Windows Millennium Edition For the first time, built-in support for local networks based on IEEE-1394 controllers appeared. Such a network has a data transfer speed four times greater than Fast Ethernet and is very convenient for a home or small office. The only inconvenience when building such a network is the short maximum length of one segment (cable length up to 4.2 m). To eliminate this drawback, signal amplifiers - repeaters, as well as multiplier-hubs for several ports (up to 27) are produced. With IEEE-1394 interface Lately The new USB interface (version 2.0) is actively competing, which provides data transfer at speeds of up to 480 Mbit/s versus the old 12 Mbit/s, that is, 40 times faster than the existing USB standard! The USB bus has become widespread due to its low cost and powerful support in the form of a controller built directly into chipsets for motherboards. At the same time, it was stated that high-speed USB 2.0 would also be implemented in the form of a controller built into the chipset (Intel ICH3). However, Microsoft has announced that it will prioritize support for the IEEE-1394 interface rather than USB 2.0, and, in addition, the asynchronous nature of USB transmission does not allow it to seriously compete with FireWire in the field of digital video.

Thus, IEEE-1394 remains the international standard for a low-cost interface that allows you to integrate all kinds of digital entertainment, communications and computing devices into a consumer digital multimedia system. In other words, all IEEE-1394 devices, such as digital photo and video cameras, DVD devices and other devices, are perfectly connected to both personal computers, equipped with a similar interface (both Mac and PC computers support it), and among themselves. This means that users can now transfer, process and save data (including images, sound and video) from high speed and virtually no degradation in quality. All these distinctive features of IEEE-1394 make it the most attractive universal digital interface of the future.

http://www.videodive.ru/scl/ieee1394.shtml http://www.youtube.com/watch?v=3fLggMWeiVQ(video about how to remake an IEEE 1394 connector) http://www.youtube.com/watch?v=xrJA54IdREc(video about a laptop with IEEE 1394 connectors)

PAL, SECAM and NTSC- these are systems in which a signal is broadcast from an antenna, cable receiver, satellite receiver or DVD.

PAL, SECAM and NTSC- These are systems of chromaticity or color transmission. If they are incompatible between the signal source and the TV, the picture on the screen will be black and white, or may be narrowed or have stripes without standard image. The signal itself, which the TV circuit processes, contains information about brightness And chromaticity. Color information is encoded into one of the systems PAL, SECAM...

To get a color image, only three colors are enough: red , blue And green. That's why, television signal must contain information about these three colors and the signal brightness.

Knowing the brightness information Y, as well as the blue signal IN colors and red R, you can, through a simple calculation, find out information about the color green G.

  • NTSC
    As signals for transmitting color information in the system NTSC accepted color difference signals (R-Y And B-Y). The transmission of these signals is carried out in the spectrum of the brightness signal at one color subcarrier frequency, with a phase shift of 90 degrees.

    There are several standards NTSC, the most popular of which are: NTSC 4.43 And NTSC 3.58. They all have a half frame rate 60Hz(more precisely: 59.94005994 Hz), number of lines: 525 (486 - active), and the numbers: 4.43 or 3.58 - this is the frequency at which color information is transmitted (modulation frequency)

    The main disadvantage of the system is the possibility of distortions in color transmission. They cause the color tone on the TV screen to change depending on the brightness of a given area of ​​the image. For example, human faces on screen appear reddish in the shadows and greenish in the highlights. To reduce this distortion, TVs NTSC equipped with color tone regulators: TINT CONTROL. This control allows you to achieve a more natural coloring of details with a certain brightness, but the distortion of the color tone of the brighter or darker areas of the image even increases.

  • PAL
    PAL- an analog color television system, developed by an engineer from a German company and presented as a television broadcasting standard. System PAL is the main color television system in Europe.

    Main characteristics: half-frame change frequency - 50 Hz, number of lines - 625 (576 active), color subcarrier (color information) modulation frequency 4.43 MHz

    Since the number of complete frames in PAL equals 25 (per second) - this is close to 24 - standard filming frames, therefore, the process of transferring film films to the PAL television standard is as simple and convenient as possible (no need to trick extra non-existent frames, as for NTSC)

    Adding the voltage at the input of the delay line with the inverted voltage at its output eliminates the phase error (failure) and the color gamut on the TV screen looks more natural than when watching programs encoded in NTSC.

    Variety of standard PAL-60, supports a field change frequency of 60 Hz, adopted in the NTSC system, so it can work on equipment and televisions that have this frame rate.

  • SECAM
    The main advantage of the system SECAM is the absence of cross-distortion between color difference signals, achieved through their sequential transmission. However, in practice, this advantage may not always be realized due to the imperfection of the color signal switches in the decoding device. System SECAM practically insensitive to differential phase distortion, especially critical for the NTSC system. Due to the use of frequency modulation, there is high resistance to changes in the amplitude of the subcarrier that arise due to the unevenness of the AFC response of the transmission path. The NTSC system is more sensitive to such distortion, which manifests itself as a change in color saturation. For the same reasons SECAM less sensitive to variations in video tape speed.

    Several modifications of the standard are used around the world SECAM, which do not differ from each other in the way they transmit color difference signals, including so-called pre-emphasis. The only differences are the carrier frequencies of the luminance video signal, audio, and the method of sound modulation. One of the important differences now is the method of color recognition. For this purpose, they can be used as standard color recognition signals SECAM, and bursts of subcarrier pulses during horizontal blanking.

  • MESECAM
    MESECAM- is a type of system SECAM and serves to ensure that VCRs operating in the PAL standard have the ability to record programs broadcast in the SECAM system. It was not the best, but a fairly simple and inexpensive development, the need for which arose with the massive distribution of VCRs in the countries of Eastern Europe (USSR) and Asia, which received television signals in the SECAM system
  • HDTV
    HDTV (High Definition Television) is a new direction in the development of television in the world. Name in Russian - high definition television (HDTV).

Regular television assumes an image resolution of 720 by 576 pixels, and HDTV allows you to watch television programs with a resolution of up to 1920 by 1080 pixels. So the image size HDTV 5 times more than in regular television, or we can say that HDTV five times clearer than regular TV.

Another feature of the standard HDTV is that it regulates 60 progressive frames per second, while conventional TV provides only 24 (25) frames per second. This number of frames allows you to get a much softer and more natural image on the screen, especially in dynamic scenes.

The term “High Definition” appeared in the 30s of the 20th century. It was then that a qualitative leap occurred in television: systems began to be used that made it possible to abandon images with a resolution of 15 - 200 lines. In the mid-50s, the first prototypes were created. However, in order for high-definition television to become visible to the naked eye, a display with a large screen diagonal is required. The high cost of such displays hampered development HDTV for decades. Rapid development HDTV began in the mid-2000s, simultaneously with the widespread adoption of plasma and liquid crystal displays.

· 720p: 1280×720 pixels, progressive scan, aspect ratio 16:9, frequency - 24, 25, 30, 50 or 60 frames per second (this HDTV format is recommended as standard for EBU member countries);

· 1080i: 1920×1080 pixels, interlaced scanning, aspect ratio 16:9, frequency - 50 or 60 fields per second;

· 1080p: 1920x1080 pixels, progressive scan, 16:9 aspect ratio, 24, 25 or 30 frames per second.

To view HDTV movies you need HDTV TV. It could be HDTV plasma, LCD TV or HDTV projector. You can also watch on a monitor (LCD or CRT), but of all quality HDTV You won't see. Also, you need a player with support HDTV, or a powerful computer. If you want to enjoy HDTV television at home, you need to purchase a special receiver and satellite dish.

Probably no one needs to explain what place television occupies in our lives. News, entertainment and educational programs, reports from hot places, films, TV series, children's programs, advertising, finally... But as you know, you get used to good things quickly, and imagine a world without television programs (terrestrial, cable, satellite or video recordings) and even television game shows consoles are simply no longer possible. The producer (broadcaster) cares about the content of the programs, the viewer consumes - it would seem that what else is needed... But if the broadcaster thinks about who to transmit, and the viewer - what is transmitted, then there is also a third “participant” of TV communication - the TV, to whom What matters is how it is conveyed.
People remember this most often when they get their hands on a cassette with a recording in a standard that your pet doesn’t want to see point-blank, or rather, show, and if it shows, it’s in black and white. That’s when the words PAL, SECAM and NTSC come to light.
Until recently (approximately the end of the 80s), the average untrained television viewer was completely unaware of the existence of a great variety of television broadcasting systems, and the terms (abbreviations) NTSC, PAL or SECAM were used exclusively by television professionals. Only specialists and radio amateurs knew about the only SECAM system in the Soviet Union.
But with the massive appearance on our market (late 80s - early 90s) of imported VCRs, and later video cameras, the question of compatibility of imported equipment (working, as a rule, in the PAL standard, less often in NTSC) with domestic SECAM arose. -television receivers. In those years, the demand for VCRs gave rise to an entire underground industry for the production and distribution of PAL decoders. The number 4510 (the name of the PAL decoder chip made by Philips) is known and remembered by all radio amateurs who in one way or another had a hand in the “scorching” of our country. And by the mid-90s, even a schoolchild knew “who SECAM is,” and many probably remember KVN’s phrase “How low is SECAM’s PAL...”
In today's article we will try to lift the curtain and introduce the reader to the whole variety of television broadcasting systems and standards. But before we begin to present the essence, advantages and disadvantages of each of the systems, let us recall the basic principles underlying the formation of television images in general and color images in particular. (Here it makes sense to clarify what is meant by a standard and what is meant by a system. A standard means a set of technical characteristics of a video signal: frame frequency, line frequency, broadcast frequency range (MV, UHF), audio subcarrier frequency, color subcarrier frequency (4, 43 or 3.58 - only for NTSC).The color system determines only the method of encoding color information - this is PAL, SECAM, NTSC)
Perhaps it would be worth starting with cinema, which largely left its mark on the development of television. The operating principle of film projection is the sequential change of image frames on film and is based on the inertia of human vision, which does not notice the change of still images on the screen at a certain frequency (24 frames per second and higher) and perceives this discrete process as smooth. The same approach is used in television - motionless image frames replace each other on the screen with a frequency that “deceives” the viewer’s eye into believing that all movements on the screen are continuous. But then the discrepancies begin. If in cinema each frame is formed at once, in its entirety, then in television line scanning is used - each frame is divided into successive horizontal lines, from which an image is formed on the TV receiver screen. Unlike a movie screen, on which an image is projected from the outside, a TV screen reproduces an image from the inside.

Color on screen

The electron beam moves along horizontal lines from left to right and from top to bottom. The number of lines on the screen determines the vertical resolution of the kinescope. When the beam reaches the end of the line, it is extinguished and returns to the beginning. Then the process is repeated. This is how the image frame is formed.

A cathode ray tube (CRT) is the main element of any CRT television. This is essentially a glass flask from which the air has been pumped out. There is a screen on the front surface, a deflection system on the neck, and an electron gun inside the neck. The gun generates three electron beams, which scan the screen using a deflection system.


The surface of the screen is covered with photosensitive dots of red, green and blue phosphors. The points are combined into triads that form image elements - pixels. These are then used to create an image.


Each beam in a kinescope hits phosphors of its “own” color. For this, a shadow mask is used - a thin metal plate with holes. Each hole has its own triad. The electron beams are converged exactly where they pass through the shadow mask.


Interlace scanning
In a TV image, the image is formed by scanning first the odd (1, 3, 5, etc.) lines, and then the even (2, 4, 6, etc.) lines. One scan forms a half-frame. On 50 Hz TVs it takes 1/50 of a second, respectively, a full frame is formed in 1/25 of a second, i.e. Every second, 25 full frames are formed on the screen (for PAL, SECAM systems). This is enough for movements on the screen to be perceived as smooth. The line frequency is 25і625=15.625 Hz. In this case, the flickering of the image is less noticeable than with progressive scanning, but the edge shifts of the lines are noticeable during fast movements.

The figure clearly shows how color is formed on a color TV screen. Basic (primary) colors R, G and B when mixed form 7 basic ones. By controlling the brightness and ratio of primary colors, you can get any intermediate color shade on the screen.

The need to combine synchronization signals, information about color and brightness, as well as identification signals (a kind of “passport” for each system) into one channel led to the creation of a video signal standard that was very complex in structure. The bold line in the figure highlights a black-and-white TV signal, and frequency attachments (subcarriers) allow you to transmit information about color and belonging to a specific color system. At the same time, the scan synchronization signal is transmitted. In the figure this is what the TV line signal looks like for NTSC and PAL systems.

This is what color moire looks like in an image.


The frame obtained from the air clearly demonstrates what cross-distortion looks like. Large colored fields are covered with a fine mesh. Not only does it introduce color distortions, but it continuously shifts during viewing, distracting the viewer’s attention.


Features of television broadcasting systems

Distribution of color systems in different countries

The screen of a black-and-white TV has an internal phosphor (phosphor) coating of only one color, and its kinescope contains only one electron gun. Changing the beam current determines the intensity of the phosphor, resulting in different shades of white.
The inner surface of the color picture tube screen is covered with dots of three types of phosphors of primary colors - red, green or blue (R, G, B). From these three primary colors all colors and shades are formed. The brightness ratio of the phosphors determines the color individual elements Images. If, for example, the beam that illuminates the blue phosphor is turned off, and only red and green are illuminated, they are perceived by the eye as yellow. By changing the intensity of a particular electron beam, you can change color scheme Images. A color picture tube has three electron guns and, accordingly, three electron beams - one each for red, blue and green. Three electron beams scan the screen similar to one in a black and white kinescope. How the eye sees color

It can be assumed that in color television, “white” consists of equal parts of primary colors. Unfortunately, it is not. The human eye does not see all colors with equal brightness. The eye is much more sensitive to yellowish-green than to blue or red light. Due to the greater sensitivity of the eye in the green-orange part of the color spectrum, an equal percentage of red, green and blue colors will not appear white.
The phosphorus used in television screens is a color compound with 30 percent red, 11 percent blue and 59 percent green.

Luminance and Chroma Signals

At the dawn of the era of color television, it was decided to make color television programs compatible with existing black-and-white television (the existing stock of black-and-white televisions in the world simply did not allow doing otherwise). Black-and-white televisions must be able to receive color broadcasts and reproduce them as normal black-and-white ones. To achieve this, the structure of the color television signal completely repeated the black and white one, only adding additional signal color (and its recognition signals), which were easily filtered out in a black and white TV without (almost) affecting the image quality.
So, in color television there are two components of the video signal - luminance (luminance or Y) and chrominance (chrominance or C). The luminance (Y) signal is transmitted in the normal way, with full bandwidth, allowing a black-and-white TV to display a normal black-and-white picture. The chrominance signal (C) has a much smaller bandwidth allocated to it. This became possible due to the fact that the human eye has low color resolution and is not able to distinguish small colored image elements with the same accuracy as white ones.

Image brightness and saturation

Speaking about the perception of color, we must understand that the brightness signal carries information about the brightness of the object and its intermediate values, while the chrominance signal conveys information about the color hue and density (depth) of color or saturation of the image. A less saturated image looks faded on the screen, a more saturated image looks bright and juicy.

Color rendering

When transmitting a color TV signal, the chrominance (C) signal is converted into special color difference signals. Since brightness information is already transmitted, the color signal no longer needs it. This produces three color difference signals: red minus luminance (R–Y), green minus luminance (G–Y), and blue minus luminance (B–Y).
But there is no need to transmit all three chrominance signals because if two components of the complete chrominance signal are known, the third can be calculated. For example, when there is a signal consisting of 50% blue and 40% red, green should be 10% (50%+40%+x=100%; x=10%). Therefore, two color difference signals are chosen to transmit color information: R–Y and B–Y. The G–Y signal is omitted not only for reasons of economy (the number of transmission channels is reduced), but also to improve signal quality. Since the luminance signal is 59% green, G–Y should have the most low level. It would be more vulnerable to noise in the transmission system than larger R-Y and B-Y.

Crosstalk

In a TV receiver, the mutual influence of the brightness and color signals on each other is inevitable, because For full compatibility with black and white TV, you need to mix them with each other. This process leads to the appearance of colored moire and so-called crosstalk distortion. They come in two types. If the chrominance signal penetrates the luminance channel, a regular grid structure with a checkerboard pattern appears in the image. In another case, when the luminance signal penetrates the chrominance channel, it results in the appearance of colorless fringing (similar to a string of pearls) in the colored areas of the image. To eliminate or reduce crosstalk, comb filters are used to improve the separation of luminance and chrominance signals. The digital comb filter is an improvement on the analog comb filter and allows you to almost completely eliminate the interpenetration of Y- and C-signals. So far such filters are used only in NTSC and PAL.

TV broadcast systems

We have come to the moment when it is time to talk about color television broadcasting systems and standards. So, after receiving the color difference signals, they are converted into one signal at the transmitting center. How to encode color signals has been decided in various countries different ways. So different that it has led to the emergence of three main standards that are incompatible with each other.

The appearance of each new color system in the world was accompanied by humorous comments from the “public.” We present the most
known concerning the decoding of abbreviations and system names:
NTSC - Never Twice the Same Color (never the same color twice);
SECAM - System Essentially Contrary to the American Method (a system essentially opposite to the American method)
PAL - Picture At Last (finally a picture), Pay for Added Luxury (pay for additional luxury).

Reasons for incompatibility

For the TV receiver to operate, it needs a source of frame synchronization signals, which indicate to it the moment of the beginning of the frame in the TV signal. At the initial design stages, it was decided to use the mains frequency as such a source for two main reasons. Firstly, when using previously created TV power supplies, the problem of a “moving stripe” in the image could arise in the event of an inaccurate match between the frame rate and the power supply. And secondly, television studios would have big problems with flickering when creating TV programs.
Further variations of systems appeared in both camps with the advent of color broadcasting. Most countries with a 60 Hz network use the NTSC color television system developed in the United States.
Soon after NTSC its modification appeared, which was called PAL. It is adopted in most "50Hz" countries, including Western Europe (except France), as well as in some "60Hz" countries (eg Brazil).
In the late 60s, the SECAM system was developed in France, largely for political reasons (protection of domestic producers). It was widely adopted in the Eastern European bloc of countries mainly to encourage incompatibility with Western transmissions - again a political reason. The frame rate in SECAM is 50 Hz (with the exception of some of its exotic variations, which have died out for a long time today).

50 or 60? There are two main power supply frequencies used in the world - 50 Hz and 60 Hz. This immediately divided the world into two unequal camps: 25 frames per second (50 Hz) and 30 frames per second (60 Hz). Later, with the advent of color, the “60-Hz” countries made a slight adjustment and moved to a frequency of 59.94 Hz. Unfortunately, different frame rates are not the only reason for TV system incompatibility.

Features of color systems

NTSC
The NTSC color television system was developed in 1953 in the USA by the National Television Standards Committee. NTSC has also been adopted as the standard DTV system in Canada, Japan and a number of countries on the American continent. Color difference signals are used as signals for transmitting color information in the NTSC system. The transmission of these signals is carried out in the spectrum of the luminance signal on one color subcarrier.
In addition to the operational disadvantages associated with the complex principle of transmission and separation of color signals - quadrature modulation and synchronous detection, it is necessary to point out the greater susceptibility of the NTSC system to distortions of the "differential phase" and "differential gain" types. The first leads to distortions in the color tone, which changes depending on the instantaneous value of the brightness signal. The second, due to the nonlinearity of the amplitude characteristics, leads to saturation distortion.
NTSC options
In addition to the so-called “basic” NTSC M (525 lines/30 fps/3.58 MHz color subcarrier frequency), there are three more variants of this system.
The first is called NTSC 4.43 and is used in multi-standard VHS video recorders. The timing parameters of the video signal are the same as in basic NTSC M. The difference is that color coding and decoding is performed in the “PAL format”, i.e. The color subcarrier frequency is the same as in PAL (4.43 MHz). Almost no one in Russia has heard of the second, NTSC-J. This option is used in Japan. It differs from the basic NTSC M in the absence of support for blanking intervals in the active part of the line. Accordingly, its amplitude is 0.714 V instead of the 1 V accepted in NTSC (as in PAL and SECAM). The third, called "noninterlaced NTSC"

PAL
This system (Phase Alternation Line - a line with a variable phase), developed in Germany, basically contains all the ideas of the American NTSC. The peculiarity of PAL is the original way eliminating phase distortions inherent in the NTSC system.
In the PAL system, the subcarrier phase of a single color difference signal changes 180 degrees from line to line. In addition, the receiver uses a delay line for the time of one line (64 μsec). Those. There are two color signals with a relative delay of one line. A 180° change in phase from line to line leads to the fact that phase errors, identical in magnitude, have different signs. Adding the voltage at the input of the delay line with the inverted voltage at its output eliminates the phase error (failure).
Despite its obvious advantages, the main disadvantage of the PAL system is the significant complication of the TV receiver due to the introduction of additional nodes into its circuit to delay the color signal for the duration of one line and periodically change the phase of the color difference signal. It should also be noted that differential gain distortion is not compensated for in PAL.

SECAM
In 1958, the French engineer Henri de France invented a new system called SECAM (SEquential Couleur Avec Memoire), which did not have the main disadvantage of NTSC - color tone distortion caused by the nonlinearity of the frequency, phase and amplitude characteristics of the television path nodes. In SECAM, hue information is not determined by the phase relationships of the chrominance signals. In the first versions (the Henri de France system), information about the color tone was transmitted by amplitude modulation of the subcarrier. In the more advanced SECAM system, color information is transmitted using frequency modulation of the color subcarrier.
Color difference signals in SECAM are transmitted alternately: during one line - the R–Y signal, during the next - B–Y, etc. Color information for both R–Y and B–Y is “removed” through the line. It is assumed that the color information in the missing lines is identical to the neighboring ones. In other words, for color signals, a full frame contains half as many lines, which leads to a corresponding increase in the vertical size of colored small details. This will not reduce visual clarity vertically, because finer details are conveyed by the Y luminance signal with a full number of scan lines.
Thus, when sequentially (through a line) transmission of color signals in the receiver, as a result of using a memory element (delay line), three initial color signals are formed. Therefore, the system under consideration is often called sequential-simultaneous (or in French Sequential a memoire - sequential with memory).

"Political" SECAM
It is known that one of the reasons for the adoption of SECAM in France was to protect the domestic market from the “invasion” of the alien NTSC. Although the novelty of solutions and obvious advantages were also taken into account when creating the system. And in the USSR this system was adopted not least for political reasons - as long as it was not the American NTSC and the German PAL. Naturally, the Warsaw Pact countries “voluntarily” accepted SECAM (perhaps only the GDR managed to defend “its” sound standard - 5.5 MHz instead of the Soviet 6.5). In 1966, the political "feature" of SECAM came to light when the Soviet government used an agreement with France (to distribute only the SECAM system in the USSR) as an excuse to ban the American broadcaster NBC from videotaping demonstrations in Moscow. At the last minute, the USSR government demanded that NTSC recording be stopped, explaining that otherwise it would violate the agreement.

Comparison of SECAM, NTSC AND PAL systems

When comparing color television systems, the following qualitative and technical and economic indicators are usually taken into account.
1. Sensitivity to distortion
2. Color image quality
3. Compatible with black and white TV
4. Assessment of system features
5. Possibility and features of video recording
Based on these indicators, let us briefly compare existing systems.

1. The unevenness of the frequency and phase characteristics of the transmission path in the frequency range where the components of the color signal spectrum are located leads to image distortion in the NTSC system. These distortions appear on the screen in the form of fringes at the boundaries of areas that differ sharply in color. Such color fringing becomes noticeable even with small frequency distortions, despite the fact that these distortions are much less than those permissible in black and white television. For this reason, very stringent requirements are imposed on the frequency and phase characteristics of various equipment elements in the NTSC system. The above fully applies to the PAL system. The use of frequency modulation in the SECAM system for the transmission of color signals makes it possible not to require uniformity frequency characteristics more stringent requirements than for black and white television systems. All color signal distortions that arise due to uneven frequency characteristics are eliminated in the amplitude limiters of the receiver. In this respect, the SECAM system has significant advantages over the NTSC and PAL systems. And although gradation distortions in the brightness signal remain, they are no more noticeable than in black and white television. The PAL system has no advantages over NTSC in terms of differential gain distortion, since it also uses the same subcarrier modulation method.

2. When evaluating color television systems in terms of image quality, two circumstances must be taken into account. On the one hand, it is possible to compare the image quality obtained on television receivers of different systems under ideal conditions of signal transmission and reception. On the other hand, an assessment can be made by comparing images under real transmission conditions, when signal distortion occurs in the transmission path, and when the TV receiver is tuned by a TV viewer who does not have a special radio engineering education.
In the first option, we actually evaluate the potential capabilities of a color television system. In the second, we compare the quality of the images that TV viewers can see on their screens. Both assessment options are equally necessary. If we approach the evaluation from the standpoint of an ideal signal, then potentially the highest image quality is provided by NTSC. At the same time, its main disadvantage remains the reduced vertical resolution (only 525 lines) and the inability to transmit over long distances and over radio relay lines.
In real conditions of television reception, when the airwaves are replete with interference, and the remoteness of the television center only contributes to the growth of noise, priority will be in favor of SECAM - due to the fact that color signals are transmitted alternately at different times, there is almost no crosstalk distortion. Conventional radio relay lines can be used to transmit SECAM signals.
For the average ordinary user, in conditions of sufficient TV signal strength and a minimum of interference, there is almost no difference in image quality on the screens of NTSC, PAL and SECAM television receivers.

3. If earlier, when introducing color television systems, it was necessary to take into account the presence of an existing fleet of black-and-white receivers, now this point is not so relevant. There are practically no black-and-white broadcasts in the world (even old black-and-white films are broadcast with color recognition signals), and the number of black-and-white televisions produced is uncontrollably declining. A more significant reason for today's incompatibility is rather the existing fleet of color TV receivers, which are mostly adapted to work in one of the standards. It is clear that this will continue for many years, unless at one point the broadcasters who have agreed among themselves switch to a single standard (digital?), as happened not so long ago with the exotic French standard of 819 lines. Then it was simply decided to refuse to support this standard, and viewers who were left in the cold were forced to save money for new TVs. However, it is too early to ignore the “black and white” park.
Color signals form interference on the screen of a black-and-white receiver in the form of a fine grid. In NTSC its interfering effect is least noticeable, because When transmitting black and white areas of the image to NTSC, there are no color signals at all.
In SECAM, due to the use of frequency modulation, the chrominance subcarrier cannot be completely suppressed. To eliminate the interfering effect of color signals, the SECAM system uses subcarrier phase switching. This did not lead to the complete elimination of interference, but the use of color signal predistortion can significantly reduce its noticeability.
PAL, like the SECAM system, uses subcarrier phase switching. However, this measure does not completely eliminate interference, and as a result PAL system by this indicator it ranks lower than SECAM.

MESECAM - standard or system?
The abbreviation MESECAM is widely deciphered as Middle East SECAM (Middle Eastern SECAM). It was implied that it was common in the Near and Middle East. But SECAM broadcasting in these regions is no different from standard. In fact, several Arab countries accept normal SECAM (625 lines/50 Hz). The term “MESECAM” appeared in the years when the demand for VCRs began to grow sharply in the Arab region. Having the ability to not only receive native SECAM, but also PAL from neighboring countries, Arab viewers literally forced manufacturers to develop a cheap way to record SECAM programs. MESECAM was born - a way to record SECAM programs on PAL video recorders. To do this, there was no need to include a separate SECAM path in the tape recorder, which would significantly increase the cost. The price of a cheap solution was low recording quality (noise, interference, moire in the image).

4. Next, using the example of advantages and disadvantages, we will talk about technical features standards.
NTSC/525
Advantages
Higher frame rate - Using a frame rate of 30 Hz (actually 29.97 Hz) results in less noticeable image flicker.
High precision color editing - it is possible to edit any 4 fields without affecting the color.
Noise in the image is less noticeable - a better signal-to-noise ratio is achieved than in PAL/625.
Flaws
Smaller number scan lines - reduced vertical clarity, the line structure is more noticeable on screens with a large diagonal.
More pronounced moiré, dot interference, and crosstalk are due to the greater likelihood of interference with the monochrome image signal at the lower subcarrier frequency.
Tint Variation - Variations in the phase of the color subcarrier cause shifts in the color display, forcing receivers to be equipped with a Tint adjustment. Many NTSC TVs have circuits automatic adjustment shade. But by reducing its fluctuations, they bring all the colors that make up the flesh color to a certain standard value. However, some part of the color range may not be displayed correctly. Top models usually have the ability to turn off these circuits, cheaper ones do not.
Lower contrast compared to PAL - the gamma correction value is 2.2, while in PAL/625 it is 2.8.

PAL/625
Advantages
More detailed picture- a larger number of scan lines, as well as a wider bandwidth of the brightness signal.
Color stability - thanks to subcarrier phase inversion on each subsequent line, any phase distortion will be suppressed.
More high level contrast - gamma correction value 2.8 versus 2.2 in NTSC/525.
Flaws
More noticeable flicker - lower frame rate (25fps)
Noise is more noticeable - the requirement for a higher subcarrier frequency results in a worse signal-to-noise ratio in PAL/625 compared to NTSC/525.
Loss of color editing accuracy - due to the alternating phase of the color signal, editing can be carried out with an accuracy of ±4 frames (8 fields).
Reduced color saturation while hue remains the same - color accuracy is achieved by losing information about the phase difference of the hue and saturation signals (fortunately, the eye is less sensitive to changes in saturation compared to changes in hue, so this is the lesser of two evils).

SECAM/625
Advantages
Stability of shade and consistency of saturation.
Higher vertical resolution - SECAM uses a higher number of scan lines than NTSC/525.
Flaws
Flicker is more noticeable - see PAL/625.
It is not possible to mix two synchronous SECAM color signals - most TV studios in SECAM countries work in PAL and convert programs to SECAM only for broadcasting. In addition, advanced home equipment S-VHS, Hi8 records in PAL and only transcodes to SECAM during playback.
Regular noise structures in the image (mesh, etc.) - frequency modulation leads to the appearance of regular noise structures even on non-colored objects.
Reduced quality of monochrome signal - because one of the color subcarriers has a frequency of 4.25 MHz, a smaller bandwidth can be used for a monochrome signal.
Incompatibility between different versions of SECAM - some of the SECAM variants (broadcast and video) are incompatible with each other. For example, between the original French version of SECAM and the so-called Middle East SECAM. You will find a mention of this in the description of the VCR.

5. All support video recording basic systems. To record them, both single- and multi-system video recorders are produced. For example, in the States, NTSC models are widespread and multisystem models are much less common. In France, only SECAM models are still available. But the PAL system is not only widespread throughout the world, but is also necessarily recorded by any multi-system video recorder.
The peculiarity of recording in NTSC lies primarily in the speed of tape pulling, it is 33.35 mm/sec., while for PAL, SECAM this value is 23.39 mm/sec. Those. Tape consumption for NTSC recording is noticeably higher. In Russia, despite SECAM's monopoly, at least dual-system videos have been common since the advent of imported and domestic models. It’s paradoxical, but true - “pure” SECAM models have not only never been produced in Russia, there are very few of them even on sale. All the counters were filled with that same cheap MESECAM. Only in the last year or two did Thomson, and after it Samsung, begin to import “real” SECAM to Russia. It must be said that the difference in recording quality between SECAM and MESECAM is visible to the naked eye. You just need to take into account that if the records in MESECAM are more or less universal (in practice, there is incompatibility between different videos appears extremely rarely), then recording in SECAM is only compatible with a SECAM video recorder.
As for NTSC in Russia, it seems that this system is experiencing a rebirth here. With the proliferation of DVDs, NTSC recording has become relevant, despite the security of the content on the disc. The demand for multi-system video with NTSC recording began to grow. There are also videos with NTSC playback mode on a PAL TV, but due to the lack of replication in NTSC, they are less in demand.
Conclusion - the most common system for video recording in Russia is PAL (everything that is replicated in our country is recorded only in PAL). The second reason is video cameras sold in Russia that record exclusively in PAL; even digital camcorders have a built-in PAL encoder.

Interoperability of systems and transcoding

When talking about the intercompatibility of systems, one should keep in mind full or partial compatibility, i.e. the ability to receive a TV signal from one of the systems to a receiver designed for another, or a video recording of a TV program in one of the systems to a VCR designed to work in another.
In principle, since the frame rate and number of image lines are the same, when viewing an image recorded in SECAM on PAL equipment, it is possible to obtain a black and white image, and vice versa. Only transmission frequencies and differences in color coding make the systems incompatible from a broadcasting point of view. However, transcoding between PAL and SECAM is less complex than with NTSC.
Generally speaking, the possibility of obtaining a color image in one of the systems on a TV receiver designed for another is practically zero. Only partial compatibility remains, i.e. ability to view black and white images on a color receiver. In this case, it is enough that the receiver “understands” the frame rate of the original signal. The PAL/625 and SECAM/625 systems are partially compatible with each other - on any SECAM receiver you can reproduce a PAL program in black and white and vice versa. NTSC programs cannot be played on PAL and SECAM TVs, and vice versa. The exception is PAL60 mode in VCRs, in which case you can play a program recorded in NTSC 4.43. Varieties of the SECAM system (say, L and D) are incompatible with each other.

Solving the compatibility problem

There are three existing ways to “build bridges” between global television broadcasting standards.
The first is limited transcoding. You've probably already come across strange names like "NTSC Playback", "NTSC Playback on PAL TV" or "PAL60". These modes only allow you to play back the video on your TV, but you cannot copy it to another VCR. Something like defective transcoding.
The second method is full-fledged multi-system transcoding. Such transcoders allow recording and playback in any color system, regardless of the standard of the original program. In relation to a TV receiver, multisystem means nothing more than the ability to reproduce a signal encoded in any of the PAL, SECAM, NTSC systems. It often happens that one of the systems (we usually have NTSC) can only be played through the video input. A multi-system VCR must be able to play back a PAL recording as a standard PAL signal, and also record the PAL signal fed to it as a standard PAL recording. Naturally, he should be able to do the same with SECAM and NTSC.
Finally, the third way is to convert standards. Here we're talking about about transcoding, but only systems of one standard, say. For example, PAL (625/50) to SECAM or vice versa. Either NTSC 4.43 (525/60) to NTSC 3.58 or vice versa. This is the only way when video material is recorded with a complete guarantee against errors, while multi-transcoders when translating, say, 625-line PAL to 525-line NTSC extra lines they cut it out, and if it’s the other way around, they add it, that is, they distort the information.
It should be noted here that in consumer electronics, multi-system equipment has become very widespread, while the number of models of equipment for signal conversion can be counted on one hand. Such models are produced, for example, by Panasonic and Samsung. JVC also equips some of its VCRs with a transcoder, but only from SECAM to PAL during recording and vice versa during playback.

Letters and numbers...

Each of you has at least once seen TV boxes with the inscription Multisystem and a list of these systems in the form of letters: B, G, I, M, L, D, K, as well as fractional numbers 4.5, 5.5, 6.0, 6.5. What do they mean? And where does Multi come from as many as 28 systems, if there are only 3 of them?
Everything is very simple. As already mentioned, the three main systems have variations, differing in frame rate, number of lines, radio frequency range (for broadcast), the intermediate frequency of the sound and its position relative to the image carrier, the method and polarity of modulation of the image carrier. For those who want to figure it out on their own, we publish tables of systems.
As an example, let's take our native SECAM D, K: SECAM color system, frame frequency 25 Hz, number of lines 625, audio IF - 6.5 MHz, shift above the image carrier, image carrier modulation polarity is negative, used for broadcasting in the meter range (D), and decimeter (K), are currently used (in Russia and the CIS countries primarily).

What's next?

And further on the horizon are high-definition television and digital broadcasting. For the first, the considered color systems are still relevant. For digital TV, the fundamental colors (R, G, B) no longer require analog coding systems, which lead to quality degradation. The digital encoder is capable of transmitting the full spectrum of color TV signals without loss. At the receiving end, digital decoding of the primary signals occurs, which, bypassing the conversion systems, go straight to the kinescope guns. Such an image is not characterized by distortion, beating, interference of RGB channels, as well as doubling, tripling and outlining. And it doesn’t matter whether it’s satellite or cable reception. With the general introduction of digital broadcasting, the distortions inherent in the described systems and susceptibility to atmospheric and industrial interference will disappear into oblivion. In the meantime... We are forced to take into account the features of broadcasting and video recording, choosing what is better and more convenient.

| PAL(abbreviated from Phase Alternating Line) - analogue television standard. Color coding system used in television systems many countries of the world. This system has a resolution of 625 lines at 25 frames (50 fields) per second.

History of PAL

In the 1950s, with the mass production of color televisions in countries Western Europe, developers encountered a problem discovered in the NTSC standard. The system exhibited a number of shortcomings, the main one being image color shifts under poor signal reception conditions. Subsequently, alternative standards PAL and SECAM were developed to overcome the shortcomings of NTSC. The new standard was intended for color television in European countries, had a frequency of 50 fields per second (50 hertz), and did not have the disadvantages of NTSC.

The PAL standard was developed by Walter Bruch at Telefunken in Germany. The first broadcasts in the new standard were made in the UK in 1964, then in Germany in 1967.

Telefunken was later acquired by the French electronics manufacturer Thomson. The company also acquired the founder of the European SECAM standard, Compagnie Générale de Télévision. Thomson (now called Technicolor SA) holds the RCA license from the Radio Corporation of America, founder of the NTSC standard.

In television systems, the term PAL is often interpreted as 576i (625 lines/50 Hz) resolution, NTSC as 480i (525 lines/60 Hz). The markings on PAL or NTSC standard DVDs indicate the method of color transfer, although the composite color itself is not recorded on them.

Color coding

Like NTSC, the PAL system uses amplitude modulation with a balanced chroma subcarrier added to the luminance of the video signal in the form of composite video. The subcarrier frequency for PAL signal is 4.43361875 MHz, compared to 3.579545 MHz for NTSC. On the other hand, SECAM uses frequency modulation with two lines of alternative colors whose subcarriers are 4.25000 and 4.40625 MHz.

The very name of the standard " Phase Alternating Line" means that the phase portion of the color information in the video signal is restored from each line, which automatically corrects errors in signal transmission, canceling them, due to vertical resolution. Lines where color is restored are often called PAL or phase interleaved line, while as other lines are called NTSC lines.The first PAL TVs were very irritating to the human eye due to the so-called comb effect in the picture, also known as Hanover bars, which occurs due to errors in the phase.Thus, most receivers began to use chroma delay lines, storing information about the received color in each line of the picture tube.The disadvantage of the PAL system is the vertical color resolution, which is poorer than in NTSC, but since the human eye has the same color resolution, this effect is not visible.

A typical subcarrier frequency is 4.43361875 MHz and consists of 283.75 color clocks per line plus a 25 Hz offset to avoid interference. Since the line frequency is 15625 Hz (625 lines x 50 Hz / 2), the carrier color color is calculated as follows: 4.43361875 MHz = 283.75* 15625 Hz + 25 Hz.

The original color subcarrier is required for the decoder to correct for differences in color signals. Since the color subcarrier is not transmitted along with the video information, it must be generated in the receiver. In order for the phase of the generated signal to correspond transmitted information, 10 subcarrier “color flash” cycles are added to the video signal.

Advantages of PAL over NTSC

On NTSC receivers, color adjustment can be done manually. If the color is not adjusted correctly, the color display may be incorrect. The PAL standard automatically changes color. Color phase errors in the PAL system were eliminated using a 1H delay line, resulting in a reduction in color saturation that is less noticeable to the human eye than in NTSC.

However, even on PAL systems, color striping (Hanover bars) can result in grainy images due to phase errors if first generation decoders are used. Often, such extreme phase shifts do not occur. Typically, this effect is observed when obstacles arise during the passage of the signal, and is observed in heavily built-up areas. The effect is more noticeable at ultra high frequencies (UHF) than at VHF.

In the early 1970s, some Japanese manufacturers developed new decoding methods in order to avoid paying royalties to Telefunken. The Telefunken license covered any decoding method that would reduce subcarrier phase distortion. One development was to use a 1H delay line to decode only even or odd lines. For example, chrominance on odd lines was turned on directly at the decoder, preserving the delay lines. Then, on the even lines, the stored odd lines were decoded again. This method effectively converts the PAL system to NTSC. Such systems also have their disadvantages associated with NTSC and require the addition of manual control of color shades.

The PAL and NTSC standards have several different color spaces, but the color differences are ignored by the decoder.

Advantages of PAL over SECAM

The first attempts at compatibility with color televisions were made in the SECAM standard, which also had the problem of NTSC shades. It was achieved by using various methods of color transmission, namely alternative transmission of U and V vectors and modulation frequencies.

The SECAM standard is more reliable for long-distance signal transmission than NTSC or PAL. However, due to its nature, the color signal is only stored in a distorted form due to a decrease in amplitude, even in the black and white part of the image (the effect of color overlap occurs). Also PAL and SECAM receivers need delay lines.

PAL signal characteristics

The PAL-B/G signal has the following characteristics.

Types of PAL systems

PAL B PAL G, H PAL I PAL D/K PAL M PAL N
Bandwidth VHF UHF UHF/VHF* VHF/UHF VHF/UHF VHF/UHF
Number of fields 50 50 50 50 60 50
Number of lines 625 625 625 625 525 625
Active lines 576 576 582 576 480 576
Channel Bandwidth 7 MHz 8 MHz 8 MHz 8 MHz 6 MHz 6 MHz
Video bandwidth 5.0 MHz 5.0 MHz 5.5 MHz 6.0 MHz 4.2 MHz 4.2 MHz
Subcarrier color 4.43361875 MHz 4.43361875 MHz 4.43361875 MHz 4.43361875 MHz 3.5756110 MHz 3.58205625 MHz
Sound frequency 5.5 MHz 5.5 MHz 6.0 MHz 6.5 MHz 4.5 MHz 4.5 MHz

*PAL I system has never been used on VHF frequencies in the UK

VHF - Very High Frequency (VHF)

UHF - Ultra High Frequency (UHF)

PAL-B/G/D/K/I

Most countries using PAL standards broadcast at 625 lines and 25 frames per second. The systems differ only in the carrier frequency of the audio signal and the channel bandwidth. PAL B/G standards are used in most countries in Western Europe, Australia and New Zealand, Great Britain, Ireland, Hong Kong, South Africa and Macau. PAL D/K standards in most countries of Central and Eastern Europe, PAL D standard in China. Analog CCTV cameras use the PAL D standard.

The PAL B and PAL G systems are very similar. System B uses 7 MHz and wide channels on VHF, while system G uses 8 MHz and UHF. Also, systems D and K are similar: system D is used only on VHF, while system K is used only on UHF.

PAL-M (Brazil)

In Brazil, the PAL system uses 525 lines and 29.97 fps of the M system, while using an NTSC color subcarrier. The exact PAL-M color subcarrier frequency is 3.575611 MHz.

The PAL color system can also match NTSC; a 525-line (480i) image is often called PAL-60 (sometimes PAL-60/525, Quasi-PAL or Pseudo PAL). PAL is a broadcast standard, not to be confused with PAL-60.

PAL-N (Argentina, Paraguay, Uruguay)

This version of the system is used in Argentina, Paraguay and Uruguay. It occupies 625 lines/50 fields per second, the signal is from PAL-B/G, D/K, H, I. And the 6 MHz channel with a color subcarrier frequency of 3.582 MHz is very similar to NTSC.

VHS tapes recorded with PAL-N or PAL-B/G, D/K, H, I are not distinguishable due to down-conversion of the subcarriers on the tape. VHS recorded from a TV in Europe will be played back in PAL-N color. Additionally, any tape recorded in Argentina or Uruguay with a PAL-N television broadcast can be played in European countries that use PAL (Australia, New Zealand, etc.)

Typically, people in Uruguay, Argentina and Paraguay own televisions that also display the NTSC-M standard, in addition to PAL-N. Live television is also used in NTSC-M for North, Central and South America. Most DVD players sold in Argentina, Uruguay and Paraguay only play PAL discs (4.433618 MHz color subcarrier).

Some DVD players using a signal transcoder can encode NTSC-M, with some loss of image quality due to system conversion from 625/50 PAL DVD to NTSC-M format (525/60 output).

Extended features of the PAL specification, such as teletext, are implemented in PAL-N. PAL-N supports 608 closed captioning, which is designed to facilitate NTSC compatibility.

PAL-L

The PAL L (Phase Altered Audio L) standard uses the same video system with PAL-B/G/H quality (625 lines, 50 Hz, 15.625 kHz), but with throughput 6 MHz, not 5.5 MHz. This requires an audio subcarrier of 6.5 MHz. The channel spacing used for PAL-L is 8 MHz.

PAL standards compatibility

The PAL color system is typically used with video formats that have 625 lines per frame (576 visible lines, the rest used for overhead, data synchronization, and subtitles) and a refresh rate of 50 interlaced fields per second (that is, 25 full frames per second), such as B, G, H, I, and N.
PAL guarantees video compatibility. However, some of the standards (B/G/H, I and D/K) use different audio frequencies (5.5 MHz, 6.0 MHz and 6.5 MHz respectively). This may result in video without audio if the signal is transmitted via cable television. Some Eastern European countries that previously used SECAM D and K systems have switched to PAL, thereby focusing more on the video signal. As a result, it became necessary to use various sound media.


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