Church Media Q & A

In Uncategorizedby tfwm


What is a scan converter, and what things should I look for when buying one?

A scan converter is a device that takes a computer signal (like PC or MAC) and converts the resolution (640 x 480 or 800 x 600 or higher) and the computer sync to NTSC video.

Once again, in layman’s terms: it makes a computer signal a video signal.

For some churches, using the VGA (computer) input on their projector in addition to the video (NTSC) input means that they can go direct without any external converters.

The upside to going directly in the VGA input is that computer resolution looks better than video. Also, many projectors can switch (usually with a glitch such as a few seconds of black on the screen) between video and computer through a remote control.
So what’s the downside? You can’t use a video switcher to take a computer as an input. It only accepts video. Therefore, the ability to mix, wipe, dissolve and cut seamlessly between computer and video comes when the computers’ signal is ‘scan converted’ into video.

When is that important? If you’ve ever watched a TV show where the computer screen was used directly, you saw a scan converter in action. A great channel to see this done well is on ZDTV.

Several things to keep in mind regarding scan converters:

Know the maximum resolution that you intend to send to the scan converter. If you use 1024×768, make sure the scan converter accepts 1024×768 at the refresh rate that you computer’s video card supports.

Make sure the video card on your PC can output at the resolution and refresh rate that you desire.

When sending the scan-converted image to a 13-inch TV, the detail may not be very important. However, when sending it to a 9-foot x 12-foot screen, the significantly larger image means that any artifacts or ‘soft edges’ will show up many times over. Therefore, the scan converters that a consumer retail store sells may not be suitable for large screen display.

How ‘crisp’ you need the image to be is a result of the horizontal & vertical anti-flicker processing in the scan converter. The nicer the scan converter, the more levels of anti-flicker it will have. I prefer at least four levels of horizontal and five levels of vertical.

Does the scan converter have Genlock? This allows for the black-burst (or reference video) to sync up with the rest of the video system. This is only important if you are switching the scan-converted image with video on a mixer (switcher) that uses a black-burst generator.

What type of output does the scan converter offer? If there is a need for composite, Y/C, YUV, RGBHV, D1, etc. then make sure the scan converter has that type of output.

If you plan on running the cable over 75 feet, a distribution amplifier is a good idea. This will ‘boost’ the signal with the correct attenuation over distances with no quality loss. It is a shame to see bad video when an expensive scan converter was purchased to maintain image quality.

Scan Converts are available in external models, or an internal (usually PCI) computer slot. This is really up to you and your needs and your computers’ open slot availability.