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March 2008
When 'HD' isn't really high-def
Illustration by Jing and Mike Co.
Ever wonder why some HD programs seem, well, more high-def than others? It's because not all programs being billed as high-def
are of equal quality. Here's why:
Content might not be true high-def. Although more programming is being shot with high-definition video cameras or converted to high-def from movie film, there still isn't enough to fill every hour on many HD channels. No regulations require the TV stations to disclose whether you're watching true HD or converted, quasi-HD content.
A few networks, including HDNet, Universal HD, Discovery HD, and Mojo (InDemand), carry only programming shot in high-def or converted to HD from film. Others combine some native high-def content with material shot in standard-definition and "upconverted" to a quasi-HD resolution. For example, major broadcast networks shoot most prime-time series, sports, and talk shows in HD, but they shoot most news and reality shows in standard-def and convert them to quasi-HD. It falls short of true HD but can look better than standard-def converted by a 1080p set.
Standard-def programming has a squarish shape (a 4:3 aspect ratio), so it usually has bars or graphics on the sides to fill a wide screen. Stations occasionally stretch the image instead to eliminate those bars, but that distorts the proportions.
Bandwidth limits may degrade quality. HD programming requires much more data capacity than standard content, so the increase in HD content is straining TV providers, especially as many expand phone and Internet service. Providers compress the signals to varying degrees to squeeze more channels into the same bandwidth; heavy compression can reduce high-def picture quality. They might do so on the fly by "stealing" bandwidth from less data-demanding programming, such as a talk-show interview, and redistributing it to, say, a car-chase scene in an action movie on another channel.
Content might not be true high-def. Although more programming is being shot with high-definition video cameras or converted to high-def from movie film, there still isn't enough to fill every hour on many HD channels. No regulations require the TV stations to disclose whether you're watching true HD or converted, quasi-HD content.
A few networks, including HDNet, Universal HD, Discovery HD, and Mojo (InDemand), carry only programming shot in high-def or converted to HD from film. Others combine some native high-def content with material shot in standard-definition and "upconverted" to a quasi-HD resolution. For example, major broadcast networks shoot most prime-time series, sports, and talk shows in HD, but they shoot most news and reality shows in standard-def and convert them to quasi-HD. It falls short of true HD but can look better than standard-def converted by a 1080p set.
Standard-def programming has a squarish shape (a 4:3 aspect ratio), so it usually has bars or graphics on the sides to fill a wide screen. Stations occasionally stretch the image instead to eliminate those bars, but that distorts the proportions.
Bandwidth limits may degrade quality. HD programming requires much more data capacity than standard content, so the increase in HD content is straining TV providers, especially as many expand phone and Internet service. Providers compress the signals to varying degrees to squeeze more channels into the same bandwidth; heavy compression can reduce high-def picture quality. They might do so on the fly by "stealing" bandwidth from less data-demanding programming, such as a talk-show interview, and redistributing it to, say, a car-chase scene in an action movie on another channel.
