It's simple math. Let me show you what i mean. 480i = standard definition 480p = enhanced definition 1080i, 720p and 1080p = high definition Okay. i stands for interlaced, so only 1/2 of the lines appear at any given time. They alternate frames, between odd numbered lines and even numbered lines. Of course this is happening too fast for the human eye to see. You really only notice this with sporting events where items are moving very fast, like hockey pucks or soccer balls will look blurry if you pause live games. That's because the odd numbered and even numbered lines are one frame (1/60th of a second) apart. p, on the other hand, stands for progressive. A progressive scan uses all the lines all the time. So 720p shoots 720 lines of resolution all at once. 1080p shoots 1080 lines all at once. 1080p is very demanding on systems, that's why most cable companies won't broadcast in 1080p. To determine the true resolution and compare them on an even basis, whenever you see an i, divide the resolution by 2. That's how many lines are coming through at any frame rate. So 1080i means 540 odd lines are coming across, then 540 even lines. You could shoot a video in 720i, however, the resolution would not be good enough to be called "high definition". 720 / 2 = 360. So 720i would fall somewhere between standard and enhanced definition. Since it's not considered "high definition", there's absolutely no reason to broadcast in 720i at all.Why is only progressive?
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