Television standards conversion

Until the 1980s, standards conversion was so difficult that 24 frame/s 16 mm or 35mm film was the preferred medium of programming interchange.

Every second, an additional 10 fields must be generated—the converter has to create new frames (from the existing input) in real time.

With HDTV broadcasting, this is less of an issue, for the most part meaning only passing the captioning datastream on to the new source material.

The phenomenon is particularly apparent during slow, steady camera movements, which appear slightly jerky when telecined.

PAL material in which 2:2:2:2:2:2:2:2:2:2:2:3 pulldown has been applied, suffers from a similar lack of smoothness, though this effect is not usually called telecine judder.

Television systems converters must avoid creating telecine judder effects during the conversion process.

Robert Bosch GmbH's Fernseh division made a large three rack analog video standards converter.

[2] The Apollo Moon missions (late 1960s, early 1970s) used slow-scan television (SSTV) as opposed to normal bandwidth television; this was mostly done to save battery power (and transmission bandwidth, since the SSTV video from the Apollo missions was multiplexed with all other voice and telemetry communications from the spacecraft).

Later Apollo missions featured color field sequential cameras that output 60-frame/s video.

MUSE chipsets that can be used for systems conversion do exist, or can be revised for the needs of HDTV --> Analog TV converter boxes.

Moving pictures possess a lower resolution visually, based on complexity of interframe image content.

When one uses Nyquist subsampling as a standards conversion technique, the horizontal and vertical resolution of the material are reduced – this is an excellent method for converting HDTV to standard definition television, but it works very poorly in reverse.

To convert 24 frame/s film to 29.97 frame/s (presented as 59.94 interlaced fields per second) NTSC, a process called "3:2 pulldown" is used, in which every other film frame is duplicated across an additional interlaced field to achieve a framerate of 23.976 (the audio is slowed imperceptibly from the 24 frame/s source to match).

This produces irregularities in the sequence of images which some people can perceive as a stutter during slow and steady pans of the camera in the source material.

There are basically two ways to accomplish this: The framerate can be slowed from 25 to 23.976 frames per second (a slowdown of about 4%) to subsequently apply 3:2 pulldown.

To reduce conversion artefacts, more modern or expensive equipment may use sophisticated techniques.

The most basic and literal way to double lines is to repeat each scanline, though the results of this are generally very crude.

Interpolation can also be used to reduce the number of scanlines in the image by averaging the colour and intensity of pixels on neighbouring lines, a technique similar to Bilinear filtering, but applied to only one axis.

Some more advanced techniques measure the nature and degree of inter-frame motion in the source, and use adaptive algorithms to blend the image based on the results.

Adaptive interpolation requires that the converter analyzes multiple successive fields and to detect the amount and type of motion of different areas of the picture.

Consider a rotating object, where a simple straight line motion vector is of little help in predicting where the next block should match.

It can quickly be seen that the more inter frame motion introduced, the much greater the processing power required.

Block match converters can vary widely in price and performance depending on the attention to detail and complexity.

The background gets transported in the moved block as well, based on the motion vector of the baseball, What you might see is the ball with a small amount of outfield or whatever, tagging along.

Block matching requires a staggering amount of processing horsepower, but today's microprocessors are making it a viable solution.

When applied to a sample of finite values, a fast Fourier transform expresses any changes (motion) in terms of frequency components.

Since the result of the FFT represents only the inter-frame changes in terms of frequency distribution, there is far less data that has to be processed in order to calculate the motion vectors.

Very little is known about the specific conversion technologies used by these converter boxes in the PAL and NTSC regions.

Downconversion is usually required, hence very little image quality loss is perceived by viewers at the recommended viewing distance with most television sets.

Most modern DVDs are converted from 525 <--> 625 lines in this way, as it is very economical for most programming that originates at EDTV resolution.