Bridging the gap between computer screens and TV sets ... by Jim Kobylecky
The need is obvious. You might be a marketing guru with a conference room full of eager prospects. You're armed with up to the second computer charts, knockout presentation graphics and ... a tiny laptop. Or you might be an educator, striving to pique the slumbering interest of a class of Nintendo ninjas. Or you could be an elementary school Steven Speilberg, clutching your first multimedia project, wondering how to break it to your computer phobic parents.
All of you need an easier way to display your work. Something like a gigantic graphics monitor, only a bit less expensive. Some-thing that can be found in almost every motel, school or living room so you don't have to cart it around. Something remarkably similar to that big screen TV set next door. Egad! Why not use the TV? Maybe you wouldn't even need to haul the computer around. Maybe you could record your project on a VCR and slip it in Dad's Sunday Sports half time!
That rushing sound you just heard was all the old computer jocks running for the exits-an understandable, if antiquated, reaction. One that I, as an ex-corporate video producer, whole-heartedly agreed with. You see, once upon a time, during the early days of home computing, you seldom had a choice of displays. Most home computers depended on television sets for their output, and we couldn't wait until they stopped. After you've squinted at fuzzy, blocky, forty column letters and thin flickering graphics for a while, you yearn for a quill pen and parchment.
TVs were never meant to be computer terminals. Color television in North America is based on the NTSC (National Television System Committee) standard. Developed in 1953, NTSC had to be backwardly compatible with the black-and-white receivers the FCC authorized in 1941. Compare that to ENIAC, the world's first electronic digital computer. It wasn't operational until 1946 and used punched card output.
Early attempts to use televisions as output devices were fraught with technological terror. They also looked bad. There were three basic problems: Flicker, Fuzzies and Find-its (okay, it's really called Overscan).
Let's start with Flicker: motion pictures, television and computer terminals all depend on the eye's persistence of vision. The eye blends a succession of slightly changing still images to create a perception of one continuous motion. But, if those images appear a little too slowly, the eye perceives an annoying flicker. (There was a reason early movies were called flicks.)
For good 1940's technical reasons television operates at thirty frames, or complete pictures, of video each second. The eye's flicker rate, however, is about forty-eight pictures a second. To reduce flicker, television systems scan each image twice and create two fields for each frame. These fields are then interlaced (sixty fields a second) to form the frames (thirty frames a second). That's about the same as VGA displays, which refresh at sixty or seventy-two times per second. So what's the problem?
Interlacing means that only half of a television's 525 lines, 262.5, are scanned in a field. The second set of lines (the in between lines) are scanned in the second field. What happens to any detail in the picture that is, say, one pixel thick? Flicker City! The odd line blinks on in one field and off in the next, hammering at our attention. Even at sixty fields a second there is still some flicker in standard TV shows, but the comparative lack of detail hides it.
Which brings up the next problem, the Fuzzies. You pay big bucks for your PC's display to make it as sharp as possible, and your graphics card pumps the video information over hard wires. NTSC television's old broadcast philosophy doesn't have that advantage. Its picture is composed of luminance (brightness) and chrominance (color) signals shoved together with timing information into what is known as a Composite Video signal. There are technical trade-offs in this economy of bandwidth. Composite Video just can't deliver the horizontal resolution or bandwidth that VGA enjoys. Thus your crisp little graph lines, even the outlines of your font, appear smeared and second rate.
If you can find it at all. The third problem is Overscan. While the 525 lines in a complete television picture may seem impressive (after all VGA has only 480) there's a catch. Approximately 100 lines are lost to timing information and retracing. Only about 425 lines make it to the screen, and NTSC is not completely clear about which 425. Almost all TVs overscan the image, placing parts of the picture off the screen, and different manufactures have different ideas on how much of the top, bottom or sides should be kept. Television broadcasters (but not sub-titlers of foreign films) compensate by keeping important information in the central or "safe" area of the screen. Now look at your computer's screen, especially the top, sides and bottom. Most computer programs love to cram crucial information into every corner of the screen, information that presenters can't be sure any given television monitor will show.
Technology hates a good list of can'ts. If you travel with our marketing guru today, you'll see he or she is carrying a paperback-size device right alongside their laptop. By attaching this converter between a computer and the conference room's television, our guru can control the presentation directly from the laptop computer. Educators can use authoring tools to adapt video clips and games to their classrooms, then use the converter to illustrate their talk on screen with a software "marker." And our budding George Lucas? By using the converter to videotape her opus on the school's VCR, her multimedia extravaganza can be easily shown to her parents, friends and relatives.
What happened? From my point of view it's as if someone repealed the law of gravity. "Three things changed," explains Tom Hamilton, president of Consumer Technology Northwest, Inc., a local Beaverton company that's leading the revolution. "First, programs like Power Point and Harvard Graphics made it easy for anyone to create good presentations. Second, today's TVs have technological advancements that earlier TVs didn't have. And third, converter technology, both hardware and software, improved. In effect, people can now transfer presentations to television without sacrificing resolution and quality."
Consumer Technology's Presenter 3 Series represents a new generation of converters. The Presenter 3 is a small, black box that weighs under two pounds including cables and ac adapter. Basically, you just plug it in between your computer and your display monitor, run a cable to the television, turn it on and go.
What about flicker? Earlier converters reduced flicker by averaging lines or by drawing parts of two lines simultaneously. If it worked, the thin lines would either appear in both fields, or not at all. The Presenter 3 goes beyond that to use propriety algorithms called Video Stabilizer(tm) to draw a percentage of multiple lines simultaneously. No, I don't understand that either, but it seems to work. Presenter 3 screens look surprisingly stable.
Were they fuzzy? Steve Morton, Consumer Technology's Engineering VP, referred to their Sharp View(tm) circuitry as cleaning up any residual smearing that's caused by line averaging so that text is sharper, colors brighter and truer, and the resolutions higher. Again, the results bear him out. Some credit, however, needs to go to both presentation graphics and TV technology. Contemporary graphics use strong, large forms unlikely to be lost in a little smearing. And the newest TVs include S-Video ports that modern converters not only support but depend on. S-Video separates the chrominance and luminance information, eliminating the interference inherent in Composite Video. Any converter will suffer if forced to use Composite Video or, shudder, an RF connection.
Find-its? I was relieved to see that Overscan is still a problem; I was losing my faith in NTSC. The Presenter 3 Series uses directional buttons on the converter box to scroll hidden information back on the screen. Previous Presenters used software functions.
Let's say you take the plunge and bring your computer to your next class, business meeting or Toastmaster breakfast. Regard-less of the hardware or software you use, there are some general principles that will ensure the quality of your presentation:
Keep your screens simple and your characters and pictures large. Make
it easy for your audience to follow what you're saying.
Jim Kobylecky is a Beaverton-based media writer and consultant.