Barco Tech Tips: 220...240 -- Whatever It Takes! -

Barco Tech Tips: 220...240 -- Whatever It Takes!

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When you're tasked with selecting a frame rate for your seamless switcher's output, many people adopt the same attitude as Jack Butler (Michael Keaton's character in the 1983 film Mr. Mom). To paraphrase Mr. Butler's memorable quip, "59.94 Hz or 60 Hz...whatever it takes." In most professional seamless switchers, there's an excellent reason why a choice is provided between these two (seemingly close) frame rates -- and the reason is not quite as random as "whatever it takes."

Frame rate is the frequency at which imaging devices produce unique consecutive pictures, which we refer to as frames. This definition applies to images produced by video cameras, film cameras, computer graphics systems, and motion capture systems. In the film world, frame rate is expressed in frames per second (fps), while in the video and computer graphics realm, frame rate is expressed in hertz (Hz).

The 59.94 Hz frame rate comes from an NTSC (National Television Standards Committee) standard, and it's the refresh rate used for all standard definition video in the United States and numerous countries worldwide. Originally, back in "monochrome" days, the frame rate matched the power line frequency (60.00 Hz), but when color television came along, the frame rate was changed to 59.94 Hz. The FCC made this change in order to accommodate chrominance data within the interlaced video signal, to avoid interference with the audio signal, and, more important, so as not to anger consumers who had already purchased television sets. (If you'd like to get a headache and learn more about the FCC's decision back then, simply Google "Why is NTSC 59.94" and read all about it.)

While CRT (Cathode Ray Tube) television sets are now in their sunset years, we get to keep the legacy NTSC standard that was specifically designed for them.

When computer graphics cards and monitors were designed in the '80s, the available technology allowed for faster refresh rates and the use of non-interlaced (progressive) video. As technology advanced, progressive video formats migrated into projectors and large format display monitors.

The dilemma, when using a seamless switcher in a professional presentation system, is that the interlaced camera and other NTSC signals are routed to the switcher at 59.94 Hz, but the switcher's output is routed to a progressive

display. If the target display is set to 60 Hz, this seemingly small timing difference results in a "jutter" artifact -- clearly evident as a pulsating or stutter effect on screen, or as a line that moves vertically across the image.

The optimum way to deal with these artifacts is to set the switcher's output timing to match the refresh rate of the NTSC input

sources (at 59.94 Hz). The key is that this frame rate is independent of the target display's resolution. For example, you can set the output resolution to 1024 x 768 at 59.94 Hz or 1280 x 1024 at 59.94 Hz (rather than 60.00 Hz), and the display will automatically adapt to the incoming frequency. By using the NTSC refresh rate, the jutter artifacts are avoided.

To complete the equation, when selecting a seamless switcher, ensure that its output timing can be set to all combinations of frame rates to eliminate any potential issues with NTSC sources. This is not "whatever it takes," but rather a little bit of intelligent planning.


BARCO Tech Tip: Switch Hitter

During a recent meeting with a new client, I introduced our product line to the heads of their video department. While taking them through our seamless switcher product line, one of the team members expressed the lack of "quick switching" as the reason for not using that type of product in their workflow.  Their typical show solution was to sub-switch graphic sources "upstream" of a basic video production switcher.

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Barco Tech Tips

Tech Tips is sponsored by Barco, and offers insights into techniques and equipment employed by stagers working in the corporate and entertainment event market. For more information about Barco products, log onto the world of seamless switchers, the term KEY refers to a process in which part of one video image is mixed on top of another video image. Seamless switchers switch and convert multiple sources with various resolutions to a common resolution. The KEY effect in these devices is most commonly used to add titles to camera images. Another use of this effect is referred to as "Green Screen" in which an actor is filmed in front of a flat Green or Blue wall and then inserted into a virtual environment or in front of a weather map.

BARCO TECH TIP: Getting Graphical

The last couple of "tech calls" I've taken revolved around what type of graphics card the customer should select for some specific applications. When I answer these questions, I tend to take a "Switzerland" approach, and answer in very general terms and performance standards. The bottom line is that each graphics card manufacturer offers a unique spin on the same concept: delivering pictures from your PC to a display.

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BARCO Tech Tip: DVI Demystified

During one of my "dog and pony shows" last week, a question floated my way concerning the differences between the multiple DVI connectors out in the world. In answering this question - and cognizant of the fact that my deadline for this article was a mere three days away -- I chose to make this month's Tech Tip a discussion of the realities of DVI.

BARCO Tech Tip: Go Forth and Educate Thyself!

One of the best "tech tips" I can provide is to take a few hours each month and learn something new about our industry.  This education can take many forms.  For example, one could take a formal class, such as a manufacturer's training session, attend a meeting of one of the many professional associations that support the events market, or simply spend time on the web researching and browsing on various association web sites.

BARCO Tech Tip: The World in Color

In light of the convergence of Barco and High End Systems last month (pun intended), I thought it might be nice to review one of the key differences between the way the lighting and video guys look at color. These two visual mediums view the production of color in one of three main color spaces: CMY, RGB or YUV (SMPTE).

BARCO TECH TIP: Cable Wisdom: The Good, the Bad, the Repairable

It all started with a note from a friend. I received an e-mail last week from a longtime buddy about video cables. Specifically, he wanted to know if RG-59/ RGB cable ever goes bad. If so, when should he replace it? It was at this point that I wished I worked for one of the fine cable manufacturers we all know and love. Maybe that is why he asked me, instead of one of the fine cable manufacturers. In any case, I rattled off the answer that I imagine most of you are thinking right now: Cable does not go bad.