Are You Producing Legal and Valid Video?

By Paul Dubery, European Marketing Manager, Tektronix Video Business

Review contents:

Measure seven times Analog TV transmitters’ parameters measure Are You Producing Legal and Valid Video? “Beta TV Com” measuring equipment Measuring devices for terrestrial and cable television from Broadcast Arsenal Group of companies Measuring TV equipment from IMOS Company TV signals level measurers Measuring tools of Planar Company RAP-TV digital measuring system Kathrein TV signals measuring tools Leader Electronics measuring equipment for broadcast sphere Promax measuring equipment Recom-10 TV signal meter Sunrise Telecom’s measuring equipment for cable TV network analysis New devices from Tektronix Equipment from Wohler Company

Waveform monitors provide feedback on the fidelity of a video signal. They are the primary tools used for signal monitoring and maintenance of video systems and video equipment in post-production facilities and broadcast operations. Tektronix’ long history in the video industry and involvement in standards definitions has enabled us to providing efficient and reliable video and audio test equipment including a wide choice of waveform monitoring devices. Our comprehensive product portfolio supports multiple signal formats ranging from analogue composite to standard definition (SD) and high definition (HD) digital models and satisfies a broad range of applications throughout the programme production chain from camera line-up and colour balance to in-depth engineering measurements for service and maintenance.

Operational Needs

In a high-pressure creative environment, ease of use and clarity of display are essential. Telecine transfers and colour correction are examples of the processes involved in post-production of feature films, music videos, television or cinema commercials, all of which require quality, both creative and technical, to be extremely high. Production operations will also include camera shading and alignment, checking signal gamut for quality control and monitoring of colour correction operations. Anyone who performs technical or creative adjustments on cameras, for example, will be very aware of the potential problems that can occur when the RGB colour gamut is violated. Originally vibrant colours lose their brilliance when transmitted, destroying the visual impact first achieved on a computer display or studio monitor. Likewise a telecine operator will certainly need to ensure the colour rendition looks good subjectively but needs to know how to ensure that the technical quality is maintained within legal limits as well.

For the system designer, this means providing signal monitoring of video signals in editing or telecine transfer suites. This is the only way to provide continuous quality management and ensure programme material is not regularly rejected by clients.

Diamond, Arrowhead and Lightning Displays

For such operational monitoring, the Tektronix-developed Diamond, Lightning, and Arrowhead displays have become well accepted since they were first introduced in the industry-standard WFM601 Signal Monitoring family, now incorporated into latest product introductions such as the WFM700 SD/HD Signal Monitor and the recently-launched WVR600 Waveform Rasterizer. These unique displays are designed for use by non-technical personnel such as editors and colourists for monitoring technically complex signals in an easily understandable way, and are therefore equally suited for technicians and engineering staff. So how do the different displays work?

Diamond display — fitting the signal into legal RGB colour space

Tektronix’ Diamond display shows how a component signal fits into legal RGB colour space. Trigger alarms can be set to alert the operator if those RGB components would produce illegal colours when the video is converted to other formats.

Particularly in video graphics devices, the signal is created and finally displayed in an RGB format. If this format were maintained throughout the system, monitoring to detect an illegal signal would be quite straightforward — it would simply be a case of ensuring that the limits were not exceeded. Most studio systems, however, use colour difference Y’, C’b, C’r format for distribution and processing and the signal is finally converted to composite for transmission.

Diamond diagram on WFM700’s screen

The Tektronix Diamond display is produced by combining R’, G’ and B’ signals. If the video signal is in another format, the components are converted to R’, G’ and B’, which in turn can be converted into a valid and legal signal in any format that can handle 100% colour bars. The upper diamond is formed from the transcoded signal by applying B’+G’ to the vertical axis and B’-G’ to the horizontal axis. The lower diamond is formed by applying -(R’+G’) to the vertical axis and R’-G’ to the horizontal axis. The two diamonds are displayed alternately to create the double diamond display.

To display all three components predictably, they must lie between peak white (700 mV), and black (0V). Picture monitors handle excursions outside the standard range (gamut) in different ways. For a signal to be in gamut, all signal vectors must lie inside the G-B and G-R diamonds. If a vector extends outside the diamond, it is out of gamut. Errors in green amplitude affect both diamonds equally, while blue errors only affect the top and red errors only the bottom diamond. Timing errors can also be detected, using a colour bar test signal, as a bending of the bar transitions.

The Diamond display, equally suited to live signals or test signals, allows the operator to be certain that the monitored video signal will be translated into legal and valid signals in RGB colour space. Since the upper diamond in the Diamond display indicates levels of blue and green signal components and the lower diamond displays only red and green, it is easy to identify which channel or channels are in error when manipulating the RGB signal.

Also, it does not give false alarms or let severe gamut errors slip by without being displayed. The final advantage is its ability to be used as a subjective measure of the severity of a gamut violation.

Arrowhead Display — ensuring legal composite signals

In contrast to Diamond, the Arrowhead display is used for ensuring compliance with composite domain gamut limits. Alarms can be generated to warn the operator of invalid signals.

Arrowhead diagram for composite signals monitoring

Previously, the signal had to be encoded into composite and monitored in that format with an analogue waveform monitor. In contrast, the Tektronix Arrowhead display provides simulated composite gamut information directly from the component signal. The Arrowhead display plots luminance on the vertical axis, with blanking at the lower left corner of the arrow. The magnitude of the chrominance subcarrier at every luminance level is plotted on the horizontal axis, with zero subcarrier at the left edge of the arrow.

The upper sloping line forms a graticule indicating 100% colour bar total luma + subcarrier amplitudes. The lower sloping graticule indicates luminance + subcarrier extending towards sync tip. The electronic graticule provides a readable reference to measure what luminance plus colour subcarrier will be when the signal is later encoded into composite format.

An adjustable modulation depth alarm capability is provided to warn the operator that the composite signal may be approaching a limit. The video operator can now see how the component signal will be handled in a composite transmission system and make any necessary corrections in production.

Lightning Display — for VTR and system line-up

Recognising that a three-dimensional method would be desirable for monitoring the complete set of component signals, Tektronix developed a further display that provides both amplitude and interchannel timing information for the three signal channels on a single display. This is known as the Lightning display.

Lighting diagram for VTRs adjustment

The only test signal required for definitive colour measurements is the readily-available standard colour bar signal. The Lightning Display is generated by plotting luminance versus P’b or C’b in the upper half of the screen and inverted luma versus P’r or C’r in the lower half — like two vector displays sharing the same screen. The display also provides interchannel timing information by observing the green/magenta transitions.

Product Examples

Today’s video and audio production environments are increasingly hybrid, or mixed-format. As new facilities have been added to older analogue systems, serial digital component (SDI) “islands” increase in size and need to be integrated. Often, analogue and AES/EBU digital audio systems may also co-exist side by side. In addition, where post-production clients are from film, advertising or production environments, an increasing number of productions are being made in HD formats and therefore a growing number of European facilities are now adding HD capabilities to their existing SD installations.

In this increasingly complex environment, the most flexible solution is the modular approach. This allows facilities to start off with a simple set-up and add blocks of functionality as their needs grow. Tektronix’ TG700 Signal Generator platform is a good example of this approach, providing separate sync, analogue, digital, HD and audio modules which the system designer can mix and match according to the system timing and test signal needs. Anything from a simple, single-format SPG to a comprehensive service test signal generator can be achieved by choosing the appropriate modules. These modular “building blocks” can easily be added as additional facilities and signal formats need to be supported.

In a similar way, the WFM700 SD/HD Signal Monitoring platform can be configured as a simple SD/HD monitoring device or with an additional module provide full in-depth measurements of both SD and HD signals. A new module introduced very recently adds comprehensive analogue and digital audio monitoring and measurements, and upgrades are easily achieved by software downloads and/or module installation.

Making it still more user-friendly, the new platform comes with an integrated touch screen colour display, further enhancing the intuitive user interface and providing a display 50% larger than traditional cathode ray tubes (CRTs) while maintaining the expected high display quality. The familiar displays now incorporated into Tektronix’ WFM700 platform mean that anyone who has previously worked with other Tektronix signal monitors will have little difficulty in adapting to its combined SD/HD capabilities. The WFM700 is a powerful solution providing users with the functionality to manage their signal requirements today and the flexibility to cope with their likely needs in the future.

The WVR600 Waveform Rasterizer is our most recent signal monitoring product which provides the ultimate flexibility in displaying SD signals. Providing four simultaneous views of an analogue or SDI video signal on the four quadrants of a standard high-resolution SVGA display, the user can configure any view in any quadrant and immediately switch to full-screen at the push of a button. In addition to conventional waveform, vector and picture displays, the colour gamut displays described earlier are also selectable. Optional analogue or digital audio capabilities are available as well and extensive error alarms and logging capabilities make the WVR600 equally at home in edit suite or transmission playout areas. In a complex world, these products help make life more straightforward for broadcast and post-production facilities by streamlining the vital task of ensuring legal and valid signals.

For those who want to learn more about SD and HD video signal formats and digital audio, we have a growing range of educational literature available. This includes our SD/HD Primer, Colour Gamut Application Note and associated posters for ready availability of information as well as full product details. See http://www.tek.com/video_audio for full details.