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WRS MOTION PICTURE AND VIDEO LABORATORY |
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1000
Napor Boulevard,Pittsburgh Pa 15205 |
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WRS MOTION PICTURE AND VIDEO LABORATORY |
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1000
Napor Boulevard,Pittsburgh Pa 15205 |
International Standards Conversion
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Standards Conversion at WRS WRS offers Multi-standard Broadcast quality 5-field standard conversions with Deft Motion Interpolation. True Component Signal Inputs for the highest quality - True PAL / SECAM Waveform/Vectorscope Setup and Monitoring - Ideal for Broadcast, Editing, and Distribution Purposes worldwide.
Video Conversion Standards - Alphabetical by Country
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International Television Standards Not all the worlds TV receivers work in the same way. Different countries use different types of broadcast TV system, most of which are to varying extents incompatible with each other. Why Did This Happen?In order to work TV receivers require a source of field timing reference signals. These are signals that tell the TV receiver to be ready to receive the next picture in the stream of images. Early set designers decided to use the Mains power supply frequency as this source for two good reasons. The first was that with the older types of power supply, you would get rolling hum bars on the TV picture if the mains supply and power source were not at exactly the same frequency. The second was that the TV studios would have had enormous problems with flicker on their cameras when making programs. There are two Mains power frequencies widely used arround the World, 50Hz and 60Hz. This immediately divided the worlds TV systems into two distinct camps, the 25 frames per second camp (50Hz) and the 30 frames per second camp (60Hz). Later the 60Hz camp made a small adjustment and changed the field rate to 59.94Hz when they added color to the signals. The issue of field frequency remained sufficently deep rooted in both TV standards that the vested interest remained long after the original technical justification had gone. The biggest compatibility problems between TV standards remain related to the field rate; these are also the hardest problems to solve. Compounding The ProblemBeyond the initial divide between 50 and 60Hz based systems, further sub-divisions have appeared within both camps since the inception of Color broadcasting. The majority of 60Hz based countries use a technique known as NTSC originally developed in the United States by a committee called the National Television Standards Committee. NTSC works perfectly in a video or closed ciruit environment but can exhibit problems of varying hue when used in a broadcast environment. This hue change problem is caused by shifts in the color sub-carrier phase of the signal. A modified version of NTSC soon appeared which differed mainly in that the sub-carrier phase was reversed on each second line; this is known as PAL, standing for Phase Alternate Lines . PAL has been adopted by a few 60Hz countries, most notably Brazil. Among the countries based on 50Hz systems, PAL has been the most widely adopted. PAL is not the only color system in widespread use with 50Hz; the French designed a system of their own - primarily for political reasons to protect their domestic manufacturing companies - which is known as SECAM, standing for SEquential Couleur Avec Memoire. SECAM was widely adopted in Eastern Block countries to encourage incompatibility with Western transmissions - again a political motive. In general, since the field and scan rates are identical, you can expect to get a monochrome picture from a PAL video recording replayed on SECAM equipment, and vice versa.
The presence of different broadcast TV standards means that the exchange of international programming is made more difficult. Videotape made in the U.S. cannot be played in England, for example, without going through electronic standards conversion. This used to be a major problem. But with today's digital technology the process of converting from one international standard to another is rather simple. Standards conversion centers on changing the 60-fields per second (NTSC system) to the 50 fields per second ( PAL and SECAM systems) and vise versa. The solution is either to repeat or skip fields at regular intervals. The only way to effectively perform such a conversion is to be able to freeze a frame and hold it until it's the right time for it to start in the other TV system. The only viable way to hold such a large lump of signal electronically is to digitise it and store into a large block of fast computer memory. This is exactly what a digital standards converter does, with the picture quality of the converter governed by the amount of memory used and the resolution of the digitisation process. The biggest single problem to contend with when doing standards conversion is that of making the motion in the finished image look as smooth as possible. This is an extremely difficult thing to do. The solution to true motion tracking involves storing a sequence of frames for processing and extremely fast micro-processors to try and analyze the motion. Today, there are also multi-standard TV sets and VCRs available that switch from one standard to another. Converter boxes are available that translate the new digital broadcast standards to SDTV signals that can be received by non-digital TV sets. |
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