Digital TV for Dummies
Digital TV uses several resolutions to make pictures. The first is 480i. The same as analog but transmitted digitally. This is called SD or Standard Definition. It is not HD but it is digital. The next is 480p. Ahhh a new letter. The (p) stands for progressive scanning. Progressive scanning is a little different than interlaced scanning. With progressive scanning, the TV starts by painting line number 1. Then line 2, then line 3, then 4, 5, 6…and so on, until the 480th line is painted. Each line is painted progressively 1 through 480 in just 1 field to make 1 complete frame.
The advantage of progressive scanning is that it only needs half the time to make a full frame. That also means it can do it 60 times each second. That is twice as many frames per second as interlaced. In the time it takes an interlaced scan TV to make one frame, a progressive scan TV has made 2 frames. By filling in the gaps between the interlaced scan rate, you make the movement on the screen look smoother, and less jittery. Detail is clearer when anything moves fast on the screen. Perfect for sports and action movies.
Your computer screen has always used progressive scanning. That’s why computer pictures always looked better. 480p is used for standard DVD’s since the early 90’s. 480p was considered EDTV for Extended Definition TV because the progressive scanning increased the visible resolution. That’s why standard DVD’s look so much better than regular TV. They are both 480 lines, but the TV station is 480i, and the DVD is 480p.
Hi Definition Digital
Digital TV can also use 720p resolution. This means that there are 720 lines of pixels from top to bottom on the screen. It also means the pixels are smaller and closer together. This dramatically increases the details to provide full high definition. The 720 lines are scanned progressively (1 through 720 one time) at 60 frames per second.
Then you have 1080i TV’s. That means the TV scans 540 odd number lines for field 1, and then scans 540 even number lines for field 2. Then the two 540 line fields are interlaced to make 1 complete 1080 line picture. And again, the TV does this 30 times per second. Both 720p and 1080 i & p are considered full high definition video.
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