• Home
  •  > 
  • Questions
  •  > 
  • All about video standards NTSC, PAL and SECAM. PAL or NTSC - which is better, what's the difference? Television broadcast standards

All about video standards NTSC, PAL and SECAM. PAL or NTSC - which is better, what's the difference? Television broadcast standards

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. At the moment, digital standards are being refined, 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 application. 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 every 1/30 of a second passes electron beam. 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, through line, transmission of color difference signals from further recovery in the decoder by repeating the 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. Usually, after the bright areas of the image, the fringing has blue, and after dark ones - 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

    adopted in 1995 IEEE standard 1394

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 - transformation digital information to 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 a standard under serial number 1394. In Sony digital cameras, the 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 all 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. This equipment can be used to create systems by simply connecting 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 onto a mini-disc, store digital radio broadcasts received via STB, enter digital video into 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. In the meantime, Sony continues to develop the concept of a home network based on the IEEE-1394 standard, and intends to support developments with a practical orientation by releasing even more capacious, high-speed, compact components with low power consumption For wide range applications and subsequent integration into system chipsets. Today Sony demonstrates new samples consumer electronics, capable of forming a home network based on 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 home, then in 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.

Published in the fall of 2000 operating system Microsoft Windows Millennium Edition built-in support for the first time local networks based on IEEE-1394 controllers. 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.

So IEEE-1394 remains international standard inexpensive interface that allows you to connect all kinds of digital devices for entertainment, communication and computer technology into a household multimedia digital complex. 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 store data (including images, sound and video) at high speeds and with virtually no degradation in quality. All these distinctive features IEEE-1394 makes 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(abbreviated from Phase Alternating Line) - standard analogue television. A color coding system used in television systems in many countries around the world. This system has a resolution of 625 lines at 25 frames (50 fields) per second.

History of PAL

In the 1950s, during the mass production of color televisions in Western Europe, developers were faced with 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 chrominance 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" says 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 image, also known as Hanover bars, which occurs when there are 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, then 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 frequency 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 color signal differences. 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 manual control shades of color.

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 to combine with color TVs 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 signal transmission to long distances 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 frequencies(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 Western European countries, 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. Systems D and K are also 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, a signal 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. In addition, any tape recorded in Argentina or Uruguay from a PAL-N television broadcast can be played back 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

Standard PAL L (changed phase sound system L) 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.

Today's TV broadcasts offer the latest playback formats, but you still regularly hear about standards such as PAL or NTSC. Which is better and what is the difference between them? To understand this, you need to gain an understanding of each of these standards.

What is NTSC?

So, many American video recording media are in NTSC format. What is it? Today it is the color encoding system used by DVD players. Until recently, it was used by broadcast television in North America, Japan and much of South America.

As color televisions began to replace black-and-white televisions, developers began using several different methods to encode color for broadcast. However, these methods conflicted with each other and with old black-and-white televisions, which could not interpret the color signals transmitted to them. In 1953, the National Systems Committee adopted the NTSC standard, which was developed and implemented as a single standard. From that moment on, it became possible to use it throughout the country, as it became compatible with a large number various TVs. Nowadays you can still find NTSC. What does it mean? Even though modern TVs no longer use this format, they can still receive and recognize it.

What is PAL format?

Before deciding which is better - PAL or NTSC, you need to understand how they differ from each other.

The PAL format is a color encoding system used by DVD players and broadcast television in Europe, much of Asia and Oceania, Africa and parts of South America.

Phase Alternating Line or PAL formatting, along with the SECAM standard (previously used in Russia and the CIS, the image in this method is translated as sequential color with memory), was developed in the late 1950s to circumvent certain shortcomings of the NTSC system.

Since NTSC encodes color, this means that the signal may lose clarity in poor conditions, so early systems, created on this format were vulnerable to bad weather, in large buildings, and under the influence of several other factors. To solve this problem, the PAL video format was created. It works as follows: during broadcast, it changes every second line in the signal, effectively eliminating errors.

Unlike NTSC, PAL is still often used for over-the-air broadcasting in the regions in which it was adopted.

PAL or NTSC: which is better to use?

Many video editing programs, such as VideoStudio, allow you to choose what format to save your work in when burning to DVD.

Which format you should use mainly depends on your location. If you are creating videos that will be displayed around the world, NTSC by choice is safer and more comfortable. Most DVD players and other PAL-based devices can play NTSC video, but NTSC-based players usually do not support PAL.

Why are these formats still used?

The basic answer is that they are not today what they were originally created to be. It's obvious that technical problems problems that these coding systems were created to address in the 1950s are not applicable to the modern world. However, DVDs are still labeled as compatible with NTSC or PAL (see above for which one to buy and why), and the timings, resolutions, and refresh rates set on those systems are still used in modern TVs and monitors.

The main reason for this is the regionalization of content. Using different video formats acts as a layer physical protection to strengthen national copyright laws, and prevent the distribution of films and television programs in different countries without permission. In fact, this is the use of formats as a legal method of copyright protection. This phenomenon is so common that areas of distribution for video games and other interactive electronic media are often referred to as NTSC and PAL regions, although such software works fine on any type of display.

PAL, NTSC formats: what is the difference from the technical side?

Televisions display their images line by line and create the illusion of movement by displaying them slightly altered, many times per second. The broadcast signal for black and white television simply indicated the brightness level at each point along a line, so each frame was simply a signal with brightness information for each line.

Initially, televisions displayed 30 frames per second (FPS). However, when color was added to widescreen broadcasts, black-and-white TVs were unable to distinguish color information from luminance information, so they attempted to display the color signal as part of the picture. As a result, it became meaningless, and the need arose to introduce a new TV standard.

To display color without this problem, the broadcast needed to add a second chrominance signal between the luminance signal fluctuations, which would become ignored by black-and-white TVs, and color devices would look for it and display it using an adapter called a Colorplexer.

Because this extra signal was added between each frame update, it increased the amount of time it took for them to change, and the actual FPS on the display was reduced. Therefore, NTSC TV plays 29.97 frames per second instead of 30.

A PAL signal, on the other hand, uses 625 lines, of which 576 (known as a 576i signal) appear as visible lines on the TV, while a formatted NTSC signal uses 525 lines, of which 480 appear visible (480i). In PAL video, every second line has a phase change in the color signal, which causes them to equalize the frequency between the lines.

What does it mean?

In terms of effect, this means that signal corruption appears as a saturation (color level) error rather than a tint (color tone) error, as it would in NTSC video. This resulted in a more highly accurate picture of the original image. However, the PAL signal loses some vertical color resolution, making colors at line junctions appear slightly washed out, although this effect is not visible to the naked human eye. On modern DVDs, the signal is no longer encoded based on connecting lines, so there are no frequency or phase differences between the two formats.

The only real difference is the resolution and frame rate at which the video is played.

Convert from NTSC to PAL and vice versa

If PAL video is converted to NTSC tape, an additional 5 frames per second must be added. Otherwise, the image may appear choppy. For an NTSC movie converted to PAL, the opposite rules apply. Five frames per second must be removed or the on-screen action may appear unnaturally slow.

PAL and NTSC on HDTVs

For television there is a wide analog system, therefore, despite the fact that digital signals and high definition (HD) become the universal standard, their variations remain. The primary visual difference between NTSC and PAL systems for HDTV is the refresh rate. NTSC refreshes the screen 30 times per second, while PAL systems refresh the screen 30 times per second. For some types of content, especially high-resolution images (such as those generated by 3D animation), HDTVs using the PAL system may exhibit a slight tendency to "flicker". However, the picture quality is NTSC and most people won't notice any problems.

It is not encoded on a carrier wave basis, so there are no frequency or phase differences between the two formats. The only real difference is the resolution and frame rate (25 or 30) at which the video is played.

Systems NTSC, PAL, SECAM

As you know, people of different nationalities speak different languages. So with the advent of color television, “television languages” arose, that is, color television systems. There are only three of them NTSC, PAL and SECAM. The NTSC system has become widespread in countries with an alternating current frequency of 60 Hz (USA, Japan), the PAL and SECAM systems - in countries with an alternating current frequency of 50 Hz. Accordingly, the vertical scan frequency (field frequency) was chosen in such a way as to reduce the noticeability of interference from the electrical wiring of the primary network: for NTSC - 60 Hz, for PAL and SECAM - 50 Hz.

As soon as they were developed various systems color television, there was a need to transfer video materials from one system to another - transcoding, and if we talk about transcoding from a 50 Hz to 60 Hz system or vice versa - standard conversion.

The basis of analog color television is the PCTS - a full color television signal (or composite video signal), which contains information about brightness and color. In the English-language literature, the abbreviations CCVBS and CCVS are used to designate it (each company calls the signal in its own way and each believes that it is right).

It is known that any color can be obtained by “turning on” red (Red), green (Green) and blue (Blue) light sources (or RGB for short) in the required proportion. They are called primary colors for additive color synthesis. A television screen is made up of small RGB elements. But RGB signals were not chosen for color television transmission. Instead, all systems are based on the transmission of brightness signals Y and color difference signals U and V. Strictly speaking, for each system color difference signals have their own letter designations, for example, for PAL - V and U, for NTSC - I and Q, for SECAM - Dr and Db. But, as a rule, all original articles on television equipment, microcircuits, etc. use the term RGB to refer to primary color signals and YUV to refer to color difference signals. The RGB and YUV signals are interconnected by a unique relationship (system of equations), which is called a matrix. It looks like this:

R

G

B

Y

0,299

0,587

0,114

R-Y

0,701

0,587

0,114

B-Y

0,299

0,587

0,114

Moreover, the multipliers (normalizing coefficients) for U and V in each system are different:
PAL: V = 0.877 (R-Y), U = 0.493 (B-Y);
NTSC: I = V cos 33° - U sin 33°, Q = V sin 33° + U cos 33°;
SECAM: Dr = -1.9 x (R-Y), Db = 1.5 x (B-Y).

So why didn’t any of the developers of television systems follow the seemingly natural path and begin transmitting signals from the main RGB colors? There are several reasons for this, but perhaps the main two:

First, color television systems must remain compatible with the original black-and-white television systems so that color programs can be viewed normally (or nearly so) on a black-and-white television;

Secondly, the color television system should not have required a wider bandwidth for transmission than the original black-and-white television system.

How was it possible to transmit additional color information without expanding the video signal bandwidth (that is, without increasing the amount of transmitted information)? Is this possible? Strictly speaking, no. Each color television system is an example of a more or less successful compromise between trade-offs in the quality of luminance signal transmission and gains from the skillful use of the resulting bandwidth for color signal transmission. Obviously, the PCTS must carry information about brightness and color. But if you simply add Y, U and V to introduce color difference signals, then it will be impossible to separate them in the future. The main task is to mix the brightness and color signals without mutual interference and separate them without error. But by what criteria can you distinguish brightness from color in a video signal?

The peculiarity of human vision made it possible to solve this problem. It turned out that information about brightness is perceived by some photoreceptors of the eye - rods, and about color by others - cones (in television terminology, in YUV format). Moreover, the resolution of rods is much higher than that of cones. That is, if in the image the brightness contours are clearly marked, but the colors are “smeared,” then the human eye is guided by the brightness component, without noticing the “smear.” For example, cartoon characters in children's coloring books, even painted over by an unsteady child's hand, look quite neat and delight the parent's eye. But the typographic black outline gives this neatness to the drawing!

So, the brightness signal Y must be transmitted clearly, the color difference signals UV can be transmitted somewhat “smeared” (in a smaller frequency band) - the image will not suffer from this (or rather, the human eye will not notice it). To do less damage to clarity transmitted image, it was decided to use part of the high-frequency spectrum of the brightness signal to transmit color difference signals. A special notch filter attenuates the brightness signal at the selected frequency and forms a “gap” in its frequency response. Often in specialized literature such a filter is called notch, which translated from English means “notch”. And the color-difference signals go to a low-pass filter, which limits their spectrum, then to a modulator, which shifts them to a given area of ​​the frequency range (the modulation result is called the “chrominance subcarrier”), and then to the mixer, where the subcarrier fits into the “slot” prepared for it " in the spectrum of the brightness signal. The described method of luminance signal rejection, low-pass filtering and modulation of color-difference signals and addition of luminance and chrominance signals is the same for all color television systems. However, this is where the similarities end, and further each of the standards and their inherent advantages and disadvantages will be considered separately.

NTSC system

The NTSC standard was designed for a frame rate of 60 Hz (more precisely 59.94005994 Hz), 525 lines. To transmit chrominance, quadrature modulation with subcarrier suppression is used (that is, there is no chrominance subcarrier in uncolored areas). For modulation, a color subcarrier frequency of 3579545.5 Hz is used, which allows you to “place” 455 (odd number) half-cycles of the subcarrier frequency in one television line. Thus, in two adjacent NTSC lines, the chrominance subcarriers are in antiphase, and on the TV screen, the interference from the subcarrier looks like a small chessboard and is relatively unnoticeable. It should be noted that if the television line had an even number of subcarrier half-cycles, the interference would look like a stationary vertical grid and its visibility would be much higher. The applied method of reducing the noticeability of interference (each “bright” point on the screen is surrounded by “dark” ones and vice versa) is also based on the properties of human vision: from a certain distance the eye stops perceiving each point, but sees a uniformly luminous screen - this is called “averaging” or “filtering” ". Since each point is surrounded by others not only from the sides, but also from above and below, such filtering is called “two-dimensional”. Note that a notch filter (which selects a "notch") or a low-pass filter (which rejects all frequencies above the cutoff frequency), which is typically used to separate luminance and chrominance signals, performs only one-dimensional (horizontal) filtering. A feature of the NTSC system is that color information is transmitted not in the coordinate system (R-Y), (B-Y), but in the I, Q system, rotated relative to (R-Y), (B-Y) by 33°. In addition, the bandwidths for the I and Q signals were chosen differently - American engineers took into account that the human eye distinguishes small blue-green details worse than red ones, and decided to further save on color and gain on brightness.

Now - about quadrature modulation: what is it good and what is bad? As already mentioned, we cannot simply add the signals Y, U and V - we will not be able to separate them later. Therefore, it is first necessary to obtain a chrominance subcarrier by modulating the sinusoidal signal in such a way that its amplitude depends on the values ​​of the signals U and V, and the phase (relative to the original sinusoid) depends on the ratio of the values ​​of U and V to each other. Such a signal can already be added to the brightness signal, and then separated again. To do this, frequencies close to the frequency of the original sinusoid must first be attenuated in the brightness signal using a notch filter.

The luminance/chrominance separation in the NTSC system deserves special attention. It is noted that in one NTSC television line there is an odd number of half-cycles of the chromaticity subcarrier and, therefore, in two adjacent lines the subcarrier is in antiphase. Now let's assume that the image does not contain clear horizontal boundaries, that is, two adjacent lines are not very different from each other. In reality, this is a very loose assumption, which is not always true. Then, as a result of the summation of two adjacent lines, mutual suppression of the chrominance subcarriers will occur and, as a result, only a luminance signal of double amplitude will remain. By subtracting two adjacent lines, the lumina signal will be suppressed (we previously assumed that the adjacent lines are "almost the same") and will leave a double-amplitude chrominance subcarrier. Thus, as a result of addition and subtraction operations, it was possible to absolutely correctly extract the brightness and color signals from the complete NTSC signal. This method of separating brightness/chrominance is called comb filtering. The comb filter allows you to obtain a brightness signal in the full frequency band, that is, it does not require rejection of the brightness signal during encoding! It should be noted, however, that the vertical resolution of the image deteriorates by a factor of two (!), since the brightness/color signals in each line are replaced by the average value over two adjacent lines. In addition, if there are horizontal boundaries in the image, the described method of separating brightness/chrominance simply stops working, which leads to a loss of vertical clarity, accompanied by the appearance of interference from the unfiltered chrominance subcarrier (the so-called “hanging dots”). Effective filtering is possible only with ideal timing characteristics of the video signal (adjacent lines must be located exactly one below the other without horizontal bounce, called “jitter”) and have an ideal dependence of the frequency and phase of the color subcarrier on the frequency and phase of the horizontal sync pulse. The comb filter is completely inapplicable for filtering recordings played back from a VCR (Philips Data sheet Product specification SAA7152 Digital Video Comb Filter (DCF) August 1996), and even the requirements of the Russian broadcasting standard are insufficient for it. Therefore, it is impossible to use a comb filter in its pure form for processing real signals, and it will be possible to observe the ideally flat frequency response of the brightness signal that it produces only by connecting it to a television signal generator. Typically, a comb filter is always supplemented with a notch filter and an intelligent device for selecting the filtering method, depending on the quality of the video signal and image features. A notch filter for the NTSC system (as well as for the PAL system, which also uses phase modulation) can be relatively narrow-band, since with constant U and V signals the frequency of the chromaticity subcarrier is equal to the frequency of the unmodulated subcarrier and differs significantly from it only at sharp chromaticity transitions.

A few words should be said about the development of comb filters. Above we considered a two-dimensional (operating within one television field) comb filter. Two decades ago, a broadband television line delay device (namely, it is the basis of the comb filter) seemed to be the crown of scientific and technical thought. And now the existing frame memory blocks and the subcarrier phase alternation provided in NTSC not only in adjacent lines, but also in adjacent frames, make it possible to filter the image both vertically and horizontally, and in time. Note that time filtering is resistant to sharp boundaries in the image, but is sensitive to movement of boundaries in adjacent frames (motion).

Let's move on to decoding. The chrominance subcarrier, separated from the complete signal, is sent to the decoder to restore the values ​​of U and V. Let us imagine a method of quadrature modulation with subcarrier suppression in the form of some “device” with an arrow, the length of which depends on the sum of the squares of U and V, and the deviation angle depends on the ratio of the values U and V to each other. In the special case when U=0 and V=0, the length of the arrow is also zero - this is called “subcarrier suppression”. Both the “device” and its pointer rotate with the frequency of the subcarrier, and in this rotating form they arrive at the decoder. The scale by which the deviation and arrow length (U and V) are determined is located in the decoder itself. In order for the speed of rotation of the scale to coincide with the speed of rotation of the “device”, a special reference burst of pulses is transmitted at the beginning of each line - a “burst”. In this way, the decoder adjusts the rotation speed and the starting angle of the scale during the flash and reads the values ​​for U and V during the active part of the line.

What is good and what is bad about quadrature modulation? The good thing is that in bright and lightly colored areas of the image (where the eye is most picky), the interference from the chromaticity subcarrier is small, since its span is small (the length of the arrow is short). The bad thing is that the transmission path of the television signal affects the rotation speed of the “device”, and in different parts of the line - in different ways. As a result, the initial correspondence (phase) between the angle of deflection of the “device” needle and the “precise time” signals is disrupted, which leads to a violation of the color tone of fragments of the transmitted image (for example, bright fragments acquire a reddish tint, and dark ones become greenish). In addition, the image as a whole may take on a tint. In this regard, NTSC is said to be sensitive to differential phase distortion. These are distortions that occur during the transmission of a television signal. In addition, the color tone is determined by the angle of deviation of the “device” needle relative to the dial, which rotates along with the “device” and is adjusted once at the beginning of the television line. If the dial lags or rushes, error accumulates toward the end of the line, causing the right side of the television screen to turn red or blue. Here are the main advantages and disadvantages of NTSC - a system built on precise mathematical calculations, which turned out to be the most vulnerable in real-life conditions.

PAL system.

The method of transmitting color in the PAL system is not much different from NTSC and is essentially an adaptation of NTSC for the 625 line/50 field frame format. The main difference (and significant improvement) in the PAL system is the Phase Alternating Lines. To decode chrominance in the PAL system, a chrominance decoder with a one-line delay line was developed. The peculiarity of a decoder with a delay line is that the color signals are reconstructed from the sum and difference of the subcarriers received in the current and previous lines. In this case, the error accumulated in the current line is equal in magnitude and opposite in sign to the error accumulated in the delayed line. The disadvantage of such a decoder is that the chrominance signal lags behind the luminance signal vertically (chrominance creep). In addition, the chrominance spectrum in PAL is much more complex than in NTSC, making the PAL comb filter much more complex. Typically, a notch/bandpass filter is used to separate luminance/chrominance in the PAL system. The PAL system is insensitive to differential phase distortion.

The desire to improve the quality of PAL and NTSC systems led to the development of equipment in which the luminance signal and the chrominance subcarrier are transmitted over two separate wires, are not mixed anywhere and do not require separation. This two-wire method of transmitting a video signal is called S-Video or Y/C. S-Video allows you to use the full luminance frequency band (provides high horizontal resolution) and abandon the filtering that is inevitable for a composite signal when separating luminance/chrominance. Thus, the two-wire transmission method eliminates the frequency and phase distortions that accumulate during filtering. S-Video signals are not capable of over-the-air broadcasting. This is an in-studio standard with a wired connection method. It houses most studios using S-VHS equipment. We will consider the features of transcoding S-Video signals separately below.

SECAML system.

SECAM color television system is fundamentally different from NTSC and PAL systems. Just like in NTSC and PAL, chrominance information is transmitted to a subcarrier that fits into a “slot” in the luminance signal. But to transmit color information, frequency modulation of the subcarrier is used. This means that each pair of U and V values ​​corresponds to a pair of subcarrier frequencies. But if you mix (sum) two subcarriers, it will be impossible to separate them later. Therefore, assuming that the color in two adjacent lines is approximately the same, the subcarriers are transmitted in turn: in the current line - U, in the next line - V, then again U and so on. The chrominance decoder contains a delay line - a device that delays the subcarrier by one line, and during decoding, two subcarriers are received at the frequency discriminator: one related to the current line directly, and the second from the previous line through the delay line. Hence the name of the system - SECAM (Sequence de Couleur A Memoire), that is, alternating colors with memory. The consequence of this color transmission mechanism (with decimation) is half the vertical color resolution and a downward shift of color relative to brightness. In addition, at sharp horizontal color boundaries (transitions from color “a” to color “b”), “false” colors appear, since the values ​​of U and V are not averaged during transmission, but rather are thinned out. The reason for this effect is as follows: when transmitting color “a”, the RaGaBa values ​​are restored from the YaUaVa values, respectively, when transmitting color “b”, the RbGbBb values ​​are restored from the YbUbVb values. At the border of colors (more precisely, on the first line of another color), due to the delay of one of the chromaticity components in the decoder, RGB values ​​are restored from the triple YbUaVb - for one field and (due to the alternation of U and V in the fields) from the triple YbUbVa - for another field. Note that the colors UaVb and UbVa are absent in both color "a" and color "b". On a monitor screen, these distortions are clearly visible when examining horizontal color stripes, and on television broadcasts they are often visible in computer graphics, titles, etc. and have the form of individual lines flickering at a frequency of 25 Hz. To improve the transmission of small color details, differentiation (sharpening) of the edges of the U and V signals is applied (the so-called SECAM low-frequency correction), and in order to avoid excessive expansion of the frequency band of the low-frequency subcarrier, the corrected color-difference signals pass through a limiter. Thus, the SECAM system is fundamentally unable to correctly convey sharp color transitions. On the "vertical color bars" test signal, this effect appears as "gaps" between the bars and is especially noticeable between the green and magenta bars. To improve the signal-to-noise ratio of the chroma signal and optimize chrominance/luminance crosstalk, the modulated SECAM subcarrier is passed through a frequency-dependent circuit (called SECAM RF equalization or "bell"). In an RF-corrected signal, chroma edges (changes in color) are transmitted with more energy and therefore a better signal-to-noise ratio. However, this increases the visibility of the chrominance subcarrier, which appears as a characteristic “boiling” in the image immediately after the vertical color boundaries. You should pay attention to the features of the brightness/chrominance separation for the SECAM system. In the NTSC and PAL discussed above, the chrominance subcarrier is transmitted at the same frequency (for NTSC - 3.58 MHz, for PAL - 4.43 MHz). It is enough to install a filter tuned to this frequency to separate brightness and color. Moreover, in uncolored areas of the image (where the eye is most sensitive to interference), the subcarrier is suppressed and interference is fundamentally eliminated. The situation in the SECAM system is much more complicated. Firstly, there is no subcarrier suppression, that is, there is always interference from the subcarrier and it always needs to be filtered. Secondly, there is no way to isolate yourself from interference at any one frequency: SECAM frequency modulation occupies a band from 3.9 to 4.75 MHz, and the subcarrier frequency in a line of an image fragment depends only on the color of this fragment. In addition, the so-called "zero frequencies" for the U and V lines are different: 4.250 and 4.406 MHz, respectively. Thus, for reliable filtering of the brightness signal, it would be necessary to cut out a band from at least 3.9 to 4.75 MHz from the complete signal, and in fact, taking into account the finite steepness of the filters, much wider. With this approach, it would be necessary to give up the ability to transfer to full signal SECAM small details images. As a compromise, and also taking into account the different null frequencies in the SECAM decoder, a tunable filter was used that switched the notch frequency between 4.250 and 4.406 MHz from line to line and thereby cleared the uncolored (most critical) areas of the image from the chrominance subcarrier. It was assumed that in the remaining areas of the image the unsuppressed subcarrier would be masked by intense coloring. In addition, the “brightness” details of the image that fall into the delay band of the tunable filter in one line will be missed by the filter in the next line and, therefore, the viewer will see them on the TV screen.

In the process of encoding/decoding a video signal, distortions and losses inherent in one of the systems inevitably arise. Even single transcoding, and even into the same system, already requires two encodings and two decodings - distortions and losses accumulate. When transcoding from one system to another, effects of the second kind begin to appear: the advantages that one system provides cannot be transferred and used in another. The simplest example is to make a composite PAL-YUV-PAL converter to overlay titles. If you extract information about the subcarrier phase of the original signal and use it in secondary encoding, then such transcoding (both theoretically and practically) can be done without loss.

To narrow the range of tasks under consideration and be closer to practice, let’s consider what needs to be transcoded in Russia.

Conversion from/to NTSC.

NTSC signal sources are: video discs, satellite broadcasts, broadcasting Japan (in the Far East). There are practically no NTSC consumers in Russia. The amount of video that is transcoded (or perhaps more accurately "standardized") from/to NTSC to/from PAL and SECAM is small. Converting a sixty-hertz standard to a fifty-hertz standard and vice versa is a complex task, the difficulty of which lies in the need to change the decomposition standard. The newly received television signal must contain an image in those places of the television frame and at those points in time that were missed in the original signal. The simplest solution is to borrow the nearest raster line of the original signal, but this leads to “kinks” of object boundaries and “jerky” movements. Another solution is interline (two-dimensional) and interframe (three-dimensional, time) interpolation. It is free from "kinks" and "jerking", but leads to blurring of the boundaries of fast moving objects. The newest approach is the use of transducers with motion detectors. Such smart devices use algorithms to select areas in the frame and associate them with objects. From a sequence of frames, the direction, velocity, and acceleration of an object are calculated, and interpolation or predictive extrapolation is applied to the velocity and acceleration vectors. However, the described motion compensation algorithms only work in sufficiently simple cases, for example, with uniform rectilinear motion. And how will they behave when processing the scene “a ball hitting a wall” (the magnitude and direction of the object’s speed, the acceleration of the object, and at the moment of impact as a result of deformation, the shape of the object changes abruptly) or the scene “flight and rotation of a children’s ball” (one half which is painted in green, and the other - in red)?

Transcoding SECAM to PAL and PAL to SECAM..

In this case, a change in the decomposition standard is not required and the tasks of ensuring the widest bandwidth in the luminance and chrominance channels, the best signal-to-noise ratio, and the least luminance/chrominance crosstalk come to the fore. Secondary tasks include compensation for distortions introduced previous system, and treatments that subjectively improve visual perception.

Transcoding SECAM to PAL is required, as a rule, for processing and editing archives recorded in the SECAM system on PAL standard equipment. There are studios that use SECAM to PAL conversion, PAL processing, and PAL to SECAM conversion to integrate local programming into national broadcasts, although this is not a successful solution. As noted above, when decoding SECAM in television receivers a tunable “zero-frequency” notch filter SECAM is used. This filtering is acceptable for a TV, but for a transcoder it is completely insufficient. The fact is that the eye does not notice on the TV screen the fine chaotic residual grid of the unsuppressed SECAM subcarrier, but if a brightness signal of such a “degree of purification” is applied to the PAL encoder, then as a result of beating of the remnants of the SECAM subcarrier and the “new” PAL subcarrier in the colored areas of the image the interference in the form of a diagonal grid will be clearly visible. It is noteworthy that by manually rebuilding the SECAM notch filter, you can choose to clear one or another color in the transcoded image from interference. It is possible to filter the SECAM brightness signal (the subcarrier attenuation required during transcoding must be at least 40-42 dB) with traditional LC filters only by using a low-pass filter with a cutoff frequency of no higher than 3.2 MHz and a high steepness. However, with such a bandwidth, fine image details are lost forever. Digital signal processing technologies have made it possible to create a tunable filter that effectively rejects the chrominance subcarrier in SECAM. Such a filter cuts out not only “zero frequencies”, but also constantly monitors the distribution of energy in the subcarrier band and cuts out the frequency where the energy is maximum, that is, the chrominance subcarrier. It should be noted that the technique for determining the bandwidth of a SECAM decoder with a digital tracking filter using a sweep generator is not applicable. When the sweep generator frequency falls within the expected range of SECAM subcarriers, it will be completely suppressed, and when leaving this range, the filter will be continuously tuned in the 3.9-4.75 MHz band. The brightness signal obtained after digital filtering is suitable for subsequent encoding in PAL. In this case, additional rejection of the brightness signal by a notch filter is not required, since the “extra” frequencies in the signal obtained as a result of decoding are already attenuated.

Transcoding PAL to SECAM is required in the following cases: when rebroadcasting a composite PAL signal received from a satellite; when broadcasting a VHS-quality composite signal from a PAL studio; when broadcasting an S-VHS-quality signal from a PAL studio (in the first two cases, the PAL composite signal is decoded, in the third - S-Video. In the first and second cases, special attention should be paid to the method of separating the brightness/chrominance of the composite signal and its additional filtering, in the third - to reject the color signal during encoding.

To separate the brightness/chrominance of a PAL signal received from a satellite, it may be justified to use a comb filter. In this case, the widest frequency band of the brightness signal can be obtained. However, such a filter is very sensitive to the temporal instability of the video signal. For example, with an acceptable difference in the duration of adjacent lines in broadcasting of 32 nanoseconds and a period of 225 nanoseconds of the PAL color subcarrier, the phase error in two adjacent lines will be 360°/225x32=51°. Thus, instead of the expected suppression of subcarriers in antiphase sin(a)+sin(a+180°)Ї0, the remainder of the unsuppressed subcarrier will be equal to sin(a)+sin(a+180°+51°). In other words, the comb filter will lose its functionality. The traditional notch filter works stably as when processing highly stable on-air reception, and when filtering a “boosted” video signal received from a VHS video recorder, and easily provides suppression of the chroma subcarrier no worse than 40-42 dB. It is best if the transcoder provides the ability to select a filtering method depending on the quality (time characteristics) of the transcoded PAL signal. As a rule, the luminance signal obtained after filtering already has attenuation in the vicinity of the frequency of 4.4 MHz, and when SECAM encoding, additional notch may not be required. When transcoding a component S-Video signal, you do not have to worry about interference from subcarrier penetration, but you need to pay close attention to forming the correct frequency response of the luma SECAM signal before summing it with the chrominance subcarrier in the encoder. The same attention should be paid to the brightness frequency response when transcoding a composite PAL signal if titles, logos, etc. are inserted into the transcoder. in YUV or RGB components, as well as if image enhancement/restoration mechanisms are used. The requirements for the frequency response of the brightness channel of the SECAM encoder are set out in OST 58-18-96 and are intended, on the one hand, to attenuate high-frequency brightness components so that they do not “obscure” the chrominance subcarrier, on the other hand, to bring fine details to the screen images, even in a weakened form.

In addition to the necessary properties and qualities described above, the transcoder can perform some additional functions, for example:

Separate gain control in RGB or YUV components for color correction;

Aperture one- or two-dimensional correction of brightness and chrominance signals to sharpen the vertical and/or horizontal boundaries of brightness and chrominance;

Adjusting the combination of brightness and color signals horizontally and vertically, which will allow you to “put in place” the color that has “moved out” as a result of multiple transcoding;

Noise reduction: median filter - to eliminate satellite "sparks", recursive - to suppress magnetic film noise, etc.

On Russian market transcoders and converters of standards of both domestic and foreign production are presented. Among the companies specializing in their development and production, one cannot fail to mention: Snell&Wilcox, FOR.A, Vistek, JSC VNIITR, Profitt, ITM. Transcoders differ significantly both in price and in the capabilities they provide. In general, there is a clear relationship: the higher the price, the more opportunities. But it is impossible to give universal advice on which transcoder to choose “so that it suits us all,” as one of the advertisements says. For each specific case, you should choose a transcoder based on budget and the principle of minimal redundancy.

Video standards

Since we are talking about video formats has already been raised and quite a lot has already been said about it, including about analog And digital video recording formats, so I decided to talk directly about such common video standards How: NTSC, PAL And SECAM. Let's figure out how they differ from each other.

If you decide to purchase a camera abroad, especially in the US and Japan, be extremely careful. Prices in these countries are extremely attractive, only all video equipment is designed to work in NTSC(however, especially for Russian tourists there are stores selling electronics in the system PAL, but here you need to be doubly vigilant).

In this regard, it makes sense to delve deeper into the concept of such abbreviations as NTSC, PAL, SECAM.

What does "NTSC" mean?

NTSC- this is abbreviated. English National Television Standards Committee - National Television Standards Committee - standard analog color television, developed in the USA. On December 18, 1953, color television broadcasting was launched for the first time in the world using this particular systems. NTSC adopted as a color television standard ( video) also in Canada, Japan and several countries of the American continent.

Technical features NTSC:

  • number of fields - 60 Hz (more precisely 59.94005994 Hz);
  • number of lines (resolution) - 525;
  • subcarrier frequency - 3579545.5 Hz.
  • number of frames per second - 30.
  • Beam scanning is interlaced (interlacing).

What does "PAL" mean?

PAL- this is abbreviated. from English phase-alternating line - standard analog color television, developed by the engineer of the German company “Telefunken” Walter Bruch and presented as standard television ( video) broadcast in 1967.

Like all analog television ( video) standards, PAL is adapted and compatible with older monochrome (black and white) television broadcasting. In adapted analog standards In color television, an additional color signal is transmitted at the end of the monochrome television signal spectrum.

As is known from the nature of human vision, the sensation of color consists of three components: red (R), green (G) and blue (B). This color model is denoted by the abbreviation RGB. Due to the predominance of the green component of the color in the average television picture and to avoid redundant coding, R-Y difference and B-Y (Y is the overall brightness of the monochrome TV signal). In the system PAL use a color model YUV.

Both additional chrominance signals in PAL standard transmitted simultaneously in quadrature modulation (a variation of AM), the typical frequency of the subcarrier signal is 4433618.75 Hz (4.43 MHz).

In this case, each color difference signal is repeated in the next line with a phase rotation with a frequency of 15.625 kHz by 180 degrees, due to which the decoder PAL completely eliminates phase errors (typical of the system NTSC). To eliminate the phase error, the decoder adds the current line and the previous one from memory (analogue television receivers use a delay line). Thus, objectively, color television images in video standard PAL has half the vertical resolution of 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.

What does "SECAM" mean?

SECAM- this is abbreviated. from fr. Séquentiel couleur avec mémoire, later Séquentiel couleur à mémoire - sequential color with memory - standard analogue color television, first used in France. Historically, it is the first European color television standard.

Color signal as standard SECAM transferred to frequency modulation(World Cup), one color component in one television line, alternately. The previous ones are used as the missing lines R-Y signal or B-Y, respectively, receiving it from memory (in analog television receivers a delay line is used for this). Thus, objectively, color television images in the standard SECAM 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.

It is customary to decipher the abbreviation as a joke SECAM as “System Essentially Contrary to AMerican” (a system essentially opposite to the American one).

By the way, videotapes marked NTSC The quality and duration of recordings do not meet the standard PAL.