Televised Surfing

Internet boxes that allow consumers to surf the World Wide Web and use e-mail on their TV sets first appeared in retail outlets this fall. But making computer images compatible with 50-year-old television technology was not easy. A look at how patent-pending TVLens technology developed by WebTV Networks Inc. uses a series of filters to make computer images readable on a TV screen:

Challenge: The TV screen flickers when web pages are downloaded. This flicker occurs because of the discrepancy between how a TV and a computer monitor generate a picture.

TV pictures are created with a technique called interlacing, which draws odd lines on the screen first and then fills in the even lines. It takes about 1/30 of a second to draw the entire TV screen. Although your eye can see a flashing image at this speed, natural images on the screen have fuzzy edges, tricking the TV viewer into thinking the picture is being drawn at 1/60 of a second.

Computers, on the other hand, use progressive scanning in which the computer draws every line in one sweep betweeen 65 and 75 times a second. Consequently, your eye detects the edge between the odd and even fields on the TV when computer graphics are beamed onto it, causing the image to flicker.

Solution: Using a series of filters that adapt to the size and other characteristics of the image going through them, WebTV transforms computer images to trick the human visual system into thinking they are being flashed 60 times a second rather than 30.

Challenge: Viewers will get a headache if if their eyes don’t see sharp images on the screen. Because the TV was designed 50 years ago to accommodate only natural images filmed in real-life scenarios, sharp computer graphics beamed onto a TV monitor end up looking blurry. Consequently, WebTV technicians had to find a way to enhance the perceptual resolution of the image.

Solution: If viewers using WebTV walk close to their TV screen they will notice that not all of the dots are there. The system filters graphics coming in through the telephone line using image enhancement techniques that make it appear sharper to the human eye than it actually is. WebTV’s picture looks better from six feet away (the normal TV viewing distance) than it does up close.

Challenge: The TV has a color system created based on studies done in the 1930s. The colors used in web pages are designed for the 1990s, making color on WWW pages on the TV screen look washed out.

Solution: WebTV technicians got around this by transforming color on the web pages to make it compatible with the TV screen. They did so by running the web page through a filter that picks up the color in graphics and enhances it so it appears brighter on the TV screen.

Source: Steve Perlman, ceo, founder and chief technology officer of WebTV; Times and wire reports