Interlaced vs. Progressive Scan - 1080i vs. 1080p
Techquickie
·Techquickie
·2017-05-06
·
979 words · ~4 min read
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if you subscribe to a cable or satellite TV service chances are there's a toggle
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somewhere on your set top box that allows you to switch between 720p or
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1080 I but you've also probably noticed
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that most TVs and monitors advertise
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themselves as 1080p these days which doesn't match up with either of those so
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what gives you see that P you always see
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at the end of 1080p stands for
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Progressive and no I'm not talking about the insurance company or Bernie Sanders
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I'm talking about progressive scan which means it will draw all of the lines in a
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single frame of video sequentially so that each frame contains a complete
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image that fills the screen by contrast
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the little I stands for interlaced in
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which only every other line of an image
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is displayed in one frame interlaced
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signals are common not only for 1920x 1080 TV channels but they were also
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dominant back in the day of analog television where almost everyone was
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watching at 480i or 576i on CRT
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displays but why wouldn't it be more
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straightforward to display one whole image per frame well part of the reason
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was bandwidth you see only so much much
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data can be flung over the airwaves or a
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co-axial cable at Once interlaced video
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saves on bandwidth by only sending half of a complete frame at once this allowed
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older TV sets to refresh more frequently
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for smoother motion as they could show 60 half frames per second instead of 30
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full frames but modern LCD flat panel
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TVs only support Progressive scanning so
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how do they work then with interlaced 108i signals provided by cable or
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satellite TV services well the signals
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have to be what is called deinterlaced this can be done by either
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the set top box or the TV itself but
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either way it's an imperfect science you
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see the two halves of a fully interlaced
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frame aren't two halves of the exact
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same image rather they are usually
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delivered as the halves of two separate slightly different frames so when you
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put them together they don't look quite perfect and on lowquality displays this
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can show up as what's called combing in places where the two half frames don't
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match up very well TVs use processing
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tricks to help avoid really bad artifacting in deinterlaced video and
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generally it works fairly well on displays that are worth their salt and
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although many cable boxes can also de interlay signals it's typically a better
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idea to let your TV do it as cable boxes are all too often made by the lowest
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bidder and the de interlacing logic inside them won't be as good as what
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your tv offers but even with a nicer TV
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it can still be possible to notice a reduction in picture quality when
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there's rapid movement on screen such as if you're watching a sporting event
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because two half frames in sequence
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during something like a hockey game can be way out of sync due to the fast
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motion of the players many sports networks like ESPN have actually chosen
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to broadcast in 720p instead of 108i sacrificing
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resolution for better movement but come
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on lonus this is 2016 why do we have to
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sacrifice anything well due to the cost
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of upgrading systems as well as the fact that most Bourgeois viewers seem to be
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content with 1080i service we probably won't see real 1080p at 60 frames per
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second over cable and satellite anytime soon however the good news is that
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computers have no problem outputting 1080p signals so if you're one of the
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many folks who are constantly using their rigs for everything from gaming to
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watching Netflix in HD or even 4K you won't have to worry about interlacing
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