2 years ago

I bet a lot of people have heard terms like PAL, SECAM and NTSC. TVs and TV tuners in the process of tuning channels, often sin with questions about choosing one of them. The situation is aggravated when, in addition, it offers several subspecies of any of the three formats to choose from. And what to choose? And most importantly, how do all these formats differ from each other? In all this we will now understand.

There are three systems in the world analog color television - NTSC, PAL and SECAM, in many ways similar, and at the same time, differing in a number of parameters. This situation often requires the use of special decoders to convert video from one standard to another.

A television picture consists of lines (lines) displayed sequentially on the screen. A similar imaging method is called line scan, and the cycle of a complete change of the image (frame) - frame scan... The more lines on the screen, the better the vertical clarity of the image, and the higher frame rate eliminates the possible effect of flickering.

The figure shows the predominant use of color TV standards by region.

Basic parameters of TV signals

Due to the limited bandwidth of communication channels, each frame in all TV standards is transmitted in two receptions, or, as they say, consists of two fields. Initially (in the first field) even lines are displayed, then odd ones. Such scanning is called interlaced and, unlike horizontal, it somewhat degrades the image quality, but allows you to fit the TV signal into the standard bandwidth of communication channels.

The frequency spectrum of the full color TV signal is shown in the figure, from which it can be seen that the TV signal consists of luminance, color and sound signalstransmitted over communication channels using separate carrier frequencies. The main differences between the standards are in the methods of color coding based on modulation of the carrier frequency of the color signal.

When displaying the received TV signal, the color component is superimposed on the luminance component. Therefore, when using equipment that does not support this or that standard, usually it is possible to obtain at least black and white picture... The audio carrier frequency can be different even in variants of the same standard, which is sometimes the reason for the lack of sound during normal video playback.

NTSC

This color television standard ( NTSC) developed in the USA. The first version appeared back in 1941, and regular TV broadcasts began in 1954. NTSCthe largest, at that time, electronic companies that were members of the national committee on television systems (eng. National Television System Committee (NTSC)). The current standard NTSCused in most of the American continent as well as in Japan, South Korea, in Taiwan and the Philippines.

Two options are widely used NTSC, denoted by the letter indices M and N. Historically, the first was, and is now the most common variant, NTSC M. Then came NTSC N (sometimes called PAL N), today it is used in some countries in South America. True, NTSC J also works in Japan, but this option differs slightly from the main one - NTSC M.

Main characteristics of the NTSC format

The horizontal scan rate for NTSC M is 525 lines per screen, the frame rate is 30. The video signal bandwidth is 4.2 MHz. NTSC N uses slightly more lines at 625 and a lower frame rate of 25 Hz.

System based NTSC allows you to provide high quality color images, but imposes very stringent requirements for the receiving and transmitting equipment. Due to the peculiarities of the formation of signals of this format, during decoding it is not always possible to completely separate the signal into separate components, therefore color signals are mixed with luminance. And, depending on the brightness of the image area, it can slightly change its color tone.

Phase distortions of the signal, which sometimes occur during transmission, also contribute to a not entirely natural transmission of color tone, and amplitude-frequency distortions cause a change in color saturation.

PAL

Standard PAL (eng. Phase Alternation Line) was first used in 1967 in Germany and Great Britain. Broadcasting in these countries began in slightly different versions, of which there are now even more. PAL is widely used in most countries in Western Europe, Africa, Asia, Australia and New Zealand.

In fact, PAL is an advanced NTSC system in which the sensitivity of the transmitted signal to phase distortion is eliminated by changing the modulation method of the color carrier frequency. True, this led to some deterioration in clarity, which is partially offset (in some versions of the standard) by the increased number of lines.

The PAL standard has the largest number of used varieties.

SECAM

Standard SECAM(French. Sequential Couleur Avec Memoire) - Sequential color transfer with memory was developed in France. Regular broadcasting with its use began in 1967, in France and the USSR. IN SECAM 625 lines are used at 25 frames, or 50 fields per second. Now SECAM used in France and some countries of Europe, some countries of the former CCCP and Africa.

The peculiarity of the system is that color-difference signals are transmitted by means of frequency modulation. Whereas PAL and NTSC use quadrature amplitude modulation. Frequency modulation, as well as alternate (through a line) transmission of two color signals made it possible to get rid of excessive sensitivity to distortion, but slightly worsened the clarity, which, however, in the reception conditions terrestrial television not always fundamental and most noticeable in cable systems. SECAM allows to achieve more natural color reproduction due to improved separation of color signals from luminance.

For recording on magnetic tape, a variation of the standard was used - MESECAM, in which the subcarriers of the color-difference signals are transferred to lower frequencies (approximately 1.1 MHz), which made it possible to minimize the influence of the inconsistency of the ribbon speed on the color quality.

Comparison of formats

A list of the main differences between the standards is summarized in the table. As you can see, there are significant differences in carrier frequencies and the total frequency band occupied in communication channels.

However, today, readers are unlikely to have to suffer seriously because of problems, incompatibility of formats. Whichever way you output video from a computer, there will almost always be a choice of at least two formats PAL or NTSC.

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

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

To obtain color image, only three colors are enough: red , blue and green ... Therefore, the television signal must contain information about these three colors and the signal. brightness.

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

• NTSC
  As signals for transmitting color information in the system NTSC accepted color difference signals (R-Y and B-Y). These signals are transmitted in the spectrum of the luminance 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 frame rate 60Hz (more precisely: 59.94005994 Hz), number of lines: 525 (486 - active), and the numbers: 4.43 or 3.58 is the frequency at which color information is transmitted (modulation frequency)

  The main disadvantage of the system is the possibility of color distortions. They cause the color tone on the TV screen to change depending on the brightness of that area of \u200b\u200bthe picture. For example, human faces on the screen are painted reddish in shadows and greenish in highlights. To reduce this distortion, TVs NTSC equipped with color tone controls: TINT CONTROL... This control allows you to achieve more natural coloring of details with a single brightness, but the color tone distortion of brighter or darker parts of the image even increases.

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

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

  Since the number of full frames in PAL equally 25 (per second) is close to 24 -m standard frames of filming, therefore - the process of transferring film films to the PAL television standard is as simple and convenient as possible (you do not need to trick unnecessary 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 NTSC-encoded programs.

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

• SECAM
  The main advantage of the system SECAM is the absence of cross-distortion between color-difference signals, achieved due to 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 NTSC systems. Due to the use of frequency modulation, high resistance to changes in the amplitude of the subcarrier arising from the unevenness of the frequency response of the transmission path. NTSC system more sensitive to such distortions, manifested as changes in color saturation. For the same reasons SECAM less sensitive to fluctuations in the speed of the video tape.

  Several modifications of the standard are used in the world SECAM, not differing from each other in the method of transmission of color-difference signals, including the so-called predistortion. Only the carrier frequencies of the brightness video signal, sound accompaniment and the method of sound modulation differ. One of the important differences nowadays is the color recognition method. For this, they can be used as standard color identification signals SECAMand subcarrier bursts during horizontal blanking.

• MESECAM
  MESECAM - is a type of system SECAM and serves to enable video recorders operating in the PAL standard 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 video recorders in the countries of Eastern Europe (USSR) and Asia, which received a television signal 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).

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

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

The term "High Definition" appeared in the 30s of the 20th century. It was then that a qualitative leap took place 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 hindered development HDTV for decades. Rapid development HDTV began in the mid-2000s, concurrently 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 a standard for the EMU member countries);

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

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

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