Trials of new system resulted in pictures less detailed than viewers expected.Many Korean viewers of the World Cup soccer tournament, which ended earlier this month, watched the games on digital high definition televisions.
There were, however, a number of complaints that the quality of image on the screen failed to meet viewers’ expectations.
Some griped that the color seemed hazy, as if a plastic bag was hanging over the screen, or fine details were blurry, or “black noise” ― a term for black square blocks ― appeared on the screen when the players were in motion.
Though the problems were real, broadcasters point out this was the first use of Multi Media System, or MMS, by the three major Korean television networks. Once these glitches are straightened out, broadcasters insist, the MMS service will prove to be a major improvement.
Digital images are transmitted in horizontal lines in either of two ways ― interlaced or progressive. The interlaced system transmits odd and even numbered lines separately and joins, or interlaces them, to make one image. The progressive system transmits the whole image at the same time. The 1,080i format has a picture with 1,920 horizontal pixels multiplied by 1,080 vertical lines. The 720p format has 1,280 horizontal pixels multiplied by 720 vertical lines. The 480p is 640 horizontal pixels multiplied by 480 lines.
A pixel is the basic unit of the composition of an image on a television screen, computer monitor or similar digital display. The higher the pixel count, the more detailed an image the viewer receives.
Using MMS, a broadcaster can transmit a single 1,080i signal within one channel or split it into two programs on the same screen, one with a 720p high definition signal and the other with a 480p standard definition signal.
Broadcasters say this provides viewers more benefits by allowing more selections to choose from. Unlike analog system broadcasting where one channel shows a single program, digital broadcasting can display several shows at the same time.
Since both 1,080i and 720p are high definition systems, the quality of image is not damaged, whereas with the 480p standard format, the quality of the image declines, causing various disturbances on the screen including the black noise.
All of this might be easier to understand when it is pictured as a flower garden being broadcast.
Let’s say the garden is 1,920 meters (2,100 yards) by 1,080 meters, the same width to height ratio as the 1,080i high definition system. The flowers on the odd lines and even lines change to new flowers in turns, giving the image more in-depth detail.
Flowers in the 1,280 by 720 garden all change at the same time in a single transmission.
Thus images that come from the 1,080i format offer better detail but are not immediate, whereas the 720p format is better for getting live feeds quickly, although details may fall a little shorter than the 1,080i.
The 1,080i format delivers information at 60 fields per second with an interlaced scan. A 720p format delivers 24 or 30 frames per second. The standard signal of 480p delivers at 24, 30 or 60 frames per second.
Both the 1,080i and 720p systems need a speed of 19-megabits per second (Mbps) to maximize the quality of their images.
It would be the same as sending a 19-ton truck of blooms to change the flowers in our imaginary garden.
On the usual high definition program, the entire 19 tons of flowers will go to the 1,080i flower garden.
The multi media system, however, splits that cargo, into two trucks carrying 13 and 6 tons of flowers.
The first 13 tons go to the 720p flower garden. The latter 6 tons goes to the standard garden.
Since the second garden is missing 13 tons of flowers, quality falls in the second bed. Even the first bed missing just under a third of its expected flowers will see the drop in quality of its images.
Yet the broadcasters say because technology is well advanced, especially in compressing techniques, viewers could enjoy a high quality show using only 13Mbps.
Instead of transmitting a single program filled with 19Mbps of data, broadcasters prefer sending two different shows at the same time on a single channel, even if the quality of the image drops. This is because broadcasters can then earn more from the commercials that run alongside the shows.
The Korea Broadcast Engineers and Technicians Association insist that the MMS system benefits viewers as it provides easy access to a range of information. Many customers counter that they bought digital televisions to enjoy a higher quality of image than analog television can provide. The viewers are not interested in watching several shows on a single program whose quality is bad. They say that although high definition transmitted programs only cover one-third of all shows shown on television, it is hard to understand why broadcasters want to increase the number of low quality channels.
Meanwhile, a digital cable television that started service last year is trying to change its transmission to high definition. During a Korean Cable Television Association conference on Jeju Island last month, participants said it would be difficult to see viewers who are accustomed to high definition transmitted shows going back to analog transmission. The cable television companies agreed that to compete with the major networks, it would be necessary to secure high quality image transmission.
by Kim Chang-woo