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 Networks
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:
I always sigh when I’m anticipating a sports broadcast, and I find out that ABC or FOX is covering it...since they do it in 720p. Whenever I see sports on NBC or CBS, the broadcasts always look so much clearer. Now, I’ll flat-out state that ABC/ESPN puts on the best sports broadcasts period in terms of graphics, announcers, and so on. However, regarding the quality of the image, ABC/ESPN cannot hold a candle to NBC and CBS. I really wish ABC and FOX would switch to 1080i for all of their broadcasts, sports or otherwise.
Doesn’t your display device’s native resolution come into play here?
My 720P projector has to scale down the 1080i stations while the 720P stations are displayed without being scaled.
I would expect 720P signals being stretched to display on a 1080i (or even 1080P) displays would also loose some quality.
Shouldn’t this be a discussion of:
720P signal on a 270P display vs. a 1080i signal on a 1080i display?
Regards,
Brian
PS - I’m waiting for native 1080P broadcast and a 1080P LED based front projector :)
I’m glad that I’m not the only one who thinks that football on Fox and ABC/ESPN looks like garbage. The video quality for the BCS games has been astonishingly bad!! 1080i looks so much cleaner. I’m really glad the Superbowl is on NBC this year - their broadcast quality is glorious!
You got your math wrong. In a 1/30th time slice, you see 1920x1080 unique pixels in 1080i, and 1280x720 pixels in 720p. You do not double the number of 720p pixels in your equation.
See, the 720p/60 (or 1080p/60) math does not apply to filmed material. All that happens is in two 1/60th of a second slices, it displays the SAME FRAME twice… So you see the same amount of unique pixels in 720p/30 and 720p/60.
In reality, you get about 27 million pixels per second in 720p vs. the 62.2 million in 1080i.
As another example, film is shot at 24fps. But when it’s shown in the theater, it’s actually displayed at 48fps to eliminate flicker. All they do is duplicate each frame. But it’s still referred to as “24p” and not “48p.”
-Pie
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The author of this article has zero understanding of how the tech works.
Only SOME video games run at 1080p at 60fps.
All filmed content runs at 30fps or 24fps, so 720p is just less resolution, at the same frame rate, as de-interlaced 1080i. Some TVs do not de-interlace properly, and so on these 720p might look better, but assuming a quality TV, 1080i is higher resolution than 720p as an incoming signal, and will look better.
www.robertruffo.com/HDTV.htm