January 02, 2009
| by Phil Lozen
For broadcast networks, there are two choices when it comes to HD telecasts: 720p and 1080i (the ATSC standard also covers 1080p but no one is broadcasting in that format currently). We breakdown the differences in the two formats and examine which TV networks use which format and why.
720p vs 1080i
720p displays 720 horizontal lines at the same time 60 times a second resulting in a progressive (hence the “p”) image display also known as 720p/60. 1080i puts 540 horizontal lines up at a time, first the even then the odd lines, resulting in an interlaced (there’s the “i”) 1,080-line picture 30 times a second, called 1080i/30. For a while before 1080p came into its own with HD DVD and Blu-ray, it was thought that 1080i was the king of the hill for HD resolution. However, 1080i is really best-suited for CRT-based HD sets that are designed for interlaced video and must be deinterlaced before being shown on a 1080p or 720p HD set.
So does that mean there’s no difference between the two since the image is being deinterlaced on nearly all HDTVs? If only it were that easy. Most of what ends up on TV is shot at 24 frames per second, except for sports and talk shows. People a lot smarter than I have done the math and for 24fps film, 1080i comes close to being a progressive image since it refreshed 30 times a second. However, for shows shot at 60fps such as live sports, there is a decided advantage to the progressive image that 720p offers.
As for deinterlacing, certainly some sets do a better job of handling the video processing than others, but in the end, there’s still 1,080 lines of resolution that are being painted on your screen. In many people’s minds - right or wrong - more pixels means a better image (think 8 megapixel digital cameras vs. 4 megapixel ones) with those extra pixels resulting in a crisper picture. Many networks seem to agree, including the one that generally showcases the best that HD has to offer: Discovery’s HD Theater.
720p is generally best suited for fast-moving action, such as sporting events. The ESPN family of networks bolsters that claim, as they broadcast in 720p. “Simply put, with 104 mph fastballs in baseball and 120 mph shots on goal in hockey, the line-by-line basis of progressive scan technology better captures the inherent fast action of sports. For ESPN, progressive scan technology makes perfect sense,” the network says on its Web site. 1080i, meanwhile, is generally thought to be ideal for shows where fast motion isn’t an issue, such as dramas and nature shows.
The vast majority of networks are broadcasting in 1080i. Our friends over at the AVS Forum have a running list of all the major networks and cable/satellite channels and their broadcast choices and as of this fall, only 22 of the listed 87 (not including PPV) have chosen 720p. A closer look reveals that of those 22, eight are owned by ABC parent Disney and nine by Fox parent company News Corp. That’s 77 percent of the channels broadcasting in 720p owned by two companies.
Here’s a look at the major broadcast networks and their choices: