Camcorder & Computer Video Magazine – April 2000

 

Computer to TV - Use a Scan Converter To Take Video From Your PC

 

By Ralph Skinner

 

Many of the articles in this magazine tend to deal with how to take video from your camcorder and put it into your computer.  But have you ever had the need to go the other way around?  Have you been in a situation where you had images on your computer screen and wished that you could display them on a regular TV or better still, record them to tape?  These situations come up more that you might think.

Here’s an example.  Many people – for a variety of reasons – use Microsoft PowerPoint, a software program that creates slide show-style presentations.  Pictures and text are combined to tell a story or communicate an important set of facts, usually about a company or an organization.  These various screens alternate from one to another with interesting wipes and transitions, text sliding in from the bottom or side, all in an effort to keep the viewer entertained and interested.

Now, imagine you had to give that presentation to a whole room bull of people.  You would need some way to take the images and place them on a larger screen, perhaps a 32-inch TV or a large-screen video projector.  The tool or device that you need to do the trick is called a scan converter.

 

NTSC and Interlaced Scan Lines

 

Computers and televisions, or video monitors, send their images to the video screen in two entirely different ways.  TVs use a system known as NTSC, which beams approximately 250 horizontal lines of video information from top to bottom across the screen, striking the pixels in the picture tube to illuminate the screen and create the picture.  It does this real fast – 30 times a second – which is what allows us to see the transmission not as beams of light and lines across the screen but as full-motion video.  However, there is one other catch.  NTSC also works by interlacing the lines.  Confused?  Let’s back up a bit.

In a single second of video there are 30 frames – or separate image screens – each one a representation of the 250 scan lines.  The 250 scan lines are spaced alternately and evenly down the screen so that in between each pair of scan lines there is room for another line.  It rakes 1/60th of a second for the first set of 250 horizontal scan lines to be beamed across the screen.  In another 1/60th of a second, a second set of scan lines is beamed forward, placed in between – or interlaced between - the first set, each one representing our two fields of video, that together make up one frame of video.  This interlacing action is almost invisible to the naked eye.  The key word here is “almost”. 

If you look closely, you can spot the interlace action as a flicker, indicating the shift from one scan to the next.  It is most evident when titling or graphics are displayed, especially if there is a border or some part of the graphic image that is only one pixel wide.  For example, consider a title with a one pixel wide black outline around white letters.  The first scan of lines hits our screen, and we see the works with their white faces and black border.  In the next fraction of a second, that black border shifts down to the line below, where it is represented on the next scan.  Sixty times a second the black edge moves up and down, first on one line, then another.  That is what our eye sees as flicker.

Why is it done this way?  Essentially, this was the system that was de eloped decades ago, agreed upon by the powers in the television industry, and established as a universal standard, at least in the U.S. and a few other countries.  Go to England and most of Europe, and they use a similar system, only with more lines per scan, called PAL.  That’s why you can’t play tapes from Europe on your VCR here in the U.S. or vice versa.

 

The Computer Monitor

 

The big difference in the way video information is sent to a computer monitor is that there is no interlacing.  All lines are beamed forward to the picture tube in one complete set.  Consequently, there is no flicker.  Each line can contain its own set of information so the computer image is capable of displaying more information, or a higher-resolution picture. 

These entirely different approaches to displaying video information are why you need a device like a scan converter to display computer-generated data on a TV screen.  It takes the computer RGB information as it goes to your computer monitor and alters it; turning it into the two sets of scan lines needed by your TV.

 

TV One and CORIOscan

 

One company that has addressed this need of consumers and business professionals is TV One.  It distributes a number of scan converters in a variety of price ranges and capabilities.  We received TV One’s mid-range unit, the CORIOscan Select (list price $495), for evaluation, and within minutes, we had our computer signal playing on a TV.  The Select package is roughly the same as TV One’s base model, the CORIOscan Connect (list price $295), with a few extra features.  The basic unit is compact and quite un-intimidating, measuring only 1.1 inches tall, 6.2 inches long and 3.8 inches wide, and weighs only 8 ounces.  CORIOscan Connect is white; CORIOscan Select is black.  Both units are supplied with the cables you need to do a basic hook-up.  CORIOscan Select also comes with a black carrying case for secure transport.  It’s the perfect package for the traveling salesperson or instructor who moves from location to location with their presentations in laptop computers.  Armed with CORIOscan, they’re ready to show their message on any available TV or video projector.

Installation of both units with a regular computer is easy.  On the back is a set of connectors.  For the basic set-up, simply take the cable going to your computer monitor and plug it in to CORIOscan at the connector marked PC In.  Take the supplied cable and go from the connector labeled PC Out and hook it up to your monitor.  The signal from your computer is looped through CORIOscan converter so that you still have your standard computer monitor as part of the system, functioning as it would normally.

Also on the back of CORIOscan are the video output connectors.  There are both composite, and RCA-style standard video output connectors, as well as those for S-Video Out.  This enables you to hook up more than one monitor at the same time or use the higher-resolution S format on compatible video monitors.

 

A Quick Explanation of S-Video

 

A number of years ago, video manufacturers were searching for a higher-resolution system for video recording.  This demand was driven by the camcorder revolution, which wanted better-quality video.  The solution was S, a video processing technology that uses the NTSC interlaced scan technology but does it with more horizontal lines, approximately 400 as compared with standard video’s 250.

Part of how this is accomplished is that the color, or chrominance, information is kept separate from the contrast, or luminance signal, not only in the circuitry but also even in the cable that feeds the monitor (unlike composite video, which is a mixture of both signals on a single cable).  Consequently you must have a video monitor that is capable of accepting an S-video input.  Most newer monitors do.  Even the majority of standard televisions these days will accept both composite and S-video, as well as traditional RF.

 

A Quick Explanation of RF

 

When television was being developed, engineers basically took the technology of radio and added video along with the audio to the radio frequency carrier.  A radio frequency that could be transmitted for miles and miles carried with it information for reproducing pictures and sound.

The same technology is still in use today.  An RF, or TV, tuner inside your television set receives the signal out of the air from an antenna or directly from your cable service and makes it available for you to see and hear broadcast transmissions.  You find each on the channel that the tuner has aligned to that specific radio frequency.

VCRs can send the video to your TV without the RF frequency as video and audio.  Unless your TV has video and audio inputs, it relies on an RF signal to display the signal from the VCR.  Because so many people only know how to hook up their TV to cable or an antenna, VCR manufacturers use an RF converter or modulator inside the VCR, which allows you to watch the video and hear the audio on channels 2, 3, or 4.  However, with the proliferation of a more video-savvy audience – video consumers familiar with high-tech toys, including camcorders, video games, DVD, and more – TV manufacturers now commonly include standard composite and S-video input connectors on most modern television sets.

 

More Features of CORIOscan

 

There are a couple of other output options provided by CORIOscan.  Often video projectors use an RGB connector as an Input, so CORIOscan makes an RGB output signal available.  Some CORIOscan models also include an RS232 connector (more on this later).

CORIOscan also allows you to choose between an NTSC or PAL output.  That’s right, the CORIOscan will output to either the U.S. NTSC or European PAL system, so no matter where you are, you’ll be ready to beam your message to the world.  Now, it’s time to look at some of the fine-tuning and other extra features that are included.

 

Underscan and Overscan

 

Let’s start out with Underscan and Overscan.  Another significant difference between the computer monitor and the television monitor is the amount of area utilized in the display.  TVs use an underscan system, with portions of the TV signal going beyond the borders that are visible.  Extra information is out there along the edges, relevant only to technicians and service people.

On a computer monitor the extra space is utilized and actually displayed on your screen.  Consequently an image created on a computer may appear cropped around the edges when displayed on the format of a standard TV screen.  When developing images for TV commercials and such, the graphics designer knows to keep all important imagery within the area known as “screen safe”, so that nothing important will be cut off when the images are seen on a TV screen.

If your presentation was not designed with “screen safe” in mind, when you hook up to CORIOscan you may find that important parts of your images disappear around the edges.  With CORIOscan, there is a simple solution.  Simply press a button on the front panel of CORIOscan to alternate between Overscan and Underscan.  Underscan will display a black border around your screen and make sure the entire computer screen is visible in the middle.

 

Autoset

 

This feature basically tells CORIOscan to analyze your computer signal and optimize it for display on the TV screen.  It looks for edges, and can be a way to fill your screen without adding the black borders of Underscan, yet it still insures that there is no information lost off the edges.  However this function can get fooled.

For example, we had a screen from a client that had a black background, with a bright picture inset.  Autoset assumed that the edge of the picture was the edge of our screen, but that was not the case.  To remedy the situation, we used the Reset to go back to the initial factory settings, then went into Manual Adjust mode to fine-tune our dimensions.

 

Freeze, Zoon and Pan

 

Pressing the Freeze button on the CORIOscan front panel or on the supplied infrared remote control freezes the computer image on the TV screen.  Zoom digitally magnifies the image by double, allowing you to show a close-up view of any portion of the image.  Pan left, right, up or down to move about the image while in the zoom mode.  These functions and others can also be activated by the supplied infrared remote control, giving the presenter freedom to move around a stage or through an audience while away from the base unit, giving access to all operations.

 

Other Models

 

As mentioned at the beginning of this article, the CORIOscan Connect is only one of several different models available.  The GL series adds a genlock, so an external video source like a camera can loop through the CORIOscan unit, allowing the computer graphics to be used as an overlay with live video. 

 

CORIOscan Select – Mouse Control

 

With the CORIOscan Select, the infrared remote can also be used to control the on-screen cursor just like a mouse.  Commands are fed to the computer through an RS232 output.  It works with the same mouse driver is your computer, so no additional software is needed.  This Select unit also provides tow composite and two S-video outputs for even more connection options.

 

CORIOscan Pro

 

This stand-alone, or rack-mount, model delivers the highest-quality output (list price $1,295) and a number of advanced features.  A six-line flicker reduction system insures that conversion from the computer video to NTSC is as smooth as possible.  YUV output allows you to send a component signal to a Betacam SP record deck.

 

VGA Theater

 

Okay, this is something different.  The VGA Theater accepts S- or composite video input from your camcorder, VCR, DVD or satellite receiver, and converts the signals so that they can be displayed on a VGA computer monitor.  There is even an RF input and built-in TV tuner, so you can watch your favorite broadcast stations on your computer.  It’s the perfect way to fit in a few minutes of the big football game or soap opera while stuck on a project at the computer.  List price on this one is only $199.

VGA In or Out, whichever way you decide to go, TV One has a solution.  In today’s multimedia world, you need to be ready for anything.  TV One’s job is to help you get there.  Enter www.tvone.com in your Internet browser’s address line and see for yourself.