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How does 1080i/p really work?

Discussion in 'DIRECTV General Discussion' started by mrfatboy, Nov 19, 2009.

  1. mrfatboy

    mrfatboy Godfather

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    For the question below please assume I'm watching true 1080i content.

    I have a 55" 1080p LED tv with an HR23. If the HR23 is set to 1080i am I seeing content at 540 lines(alternating odd/even) @30fps. Or is the HR23 displaying the full 1080 with line doubleing? Or is the hr23 displaying the 1080p with, for example, the old odd frame (540) with the new frame (540) and then alternation as such?

    I asked several people and I get different answers. What do you guys say?
     
  2. P Smith

    P Smith Mr. FixAnything

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    "I seeing content at 540 lines" - nope, it's 1080 different lines.
     
  3. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    1080i comes out with 540 lines [odd or even] followed by the other 540 lines.
    Your 55" 1080p LED tv will "buffer" these and output 1080p to the screen.
     
  4. mrfatboy

    mrfatboy Godfather

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    Does it buffer up the Odd/Even fields as a pair and then display or does it cycle thru Old Odd/New Even then Old Even/New Odd? so you are basically always looking at an old field (odd or even) pair with a new field (odd or even)?

    I hope that is clear :lol:
     
  5. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    "I think" [I should stop here :lol:] both odd & even are "grouped" [fields combined] and then displayed.
     
  6. mrfatboy

    mrfatboy Godfather

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    I would think that it would be the old/new pairing otherwise wouldn't it be 1080p. Sorry, it's cocktail time and this is giving me a headache and frustrating :lol:
     
  7. LarryFlowers

    LarryFlowers New Member

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    My question is "Why"?

    You bought a new TV.. do you like it? Does the picture look good? Are you enjoying it?

    Not sure what disecting it is going to accomplish... If you want real details call the manufacturer and ask to talk to one of their engineers.. as soon as the "experts" here discover this thread they will turn it into a raving argument.
     
  8. David MacLeod

    David MacLeod New Member

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    no we won't and you can't prove it... :)
     
  9. sigma1914

    sigma1914 Well-Known Member DBSTalk Club

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    Then, the LCD-Plasma argument will follow. Plus, a HD-Lite comment. :lol:
     
  10. mrfatboy

    mrfatboy Godfather

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    wow, i was just interested how it actually worked. 1080p has to be 1080 vertical lines of content at 60fps, correct? 1080i has to be 540 unique lines at 30fps but it sound like it either line doubles or buffers to display a full 1080 for 60fps. When you have a 120/240 htz tv I know it just replicates what you have 2 or 4 times. I'm just confused at 1080i and 1080p basics.

    Where is the tv uber guy when you need him :D
     
  11. rudeney

    rudeney Hall Of Fame

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    Your TV is displaying 60fps. A 1080i source will supply 60fps, except that each frame will only be 540 horizontal lines - every "other" line from the 1080. However, unlike old CRT's, your LCD or plasma doesn't have the ability to only draw every other horizontal line. So, it simply re-draws the missing lines form the previous frame. To clarify, let's say we are at th 39th frame. The 1080i source just sent frames 1, 3, 5, 7, 9, 11, etc. Your TV will then display line 1 from the 39th frame, line 2 from the 38th frame, then line 3 from the 39th, line 4 from the 38th, etc. On the 40th frame, you'll get line 1 from the 39th frame, line 2 form the 40th, line 3 from the 39th, line 4 from the 40th, etc.
     
  12. P Smith

    P Smith Mr. FixAnything

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    If you will search for "1080p" or "1080p24" you'll have entertaining reading for a few days. Include unique 540 lines phenomena, temporal and spatial characteristics of source signal, film-like output, etc.
     
  13. ToBeFrank

    ToBeFrank Legend

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    Do a google search for "deinterlacing". There is no one way to describe how it's done. There are several deinterlacing algorithms and it depends on what your TV implements.
     
  14. Go Beavs

    Go Beavs Hall Of Fame

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    Just make sure your mast is plumb (or not). :lol:
     
  15. djrobx

    djrobx Godfather

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    Very few modern flat panels will actually display an interlaced picture. With the exception of ALiS plasmas, they will process 1080i input and convert it to the display's native progressive resolution.

    The accuracy that this can be done depends a lot on the source material. Film material shot at 24fps can be perfectly converted back to 1080p with no loss, because no time passes between the two interlaced frames that need to be combined. The only tricky part is that to get from 24 to 60 frames per second, additional interlace frames are inserted, and must be thrown out. This is "2:3 pulldown detection".

    While Dish and DirecTV are hyping 1080p as a breakthrough in quality, it's really just a better, more efficient way to transfer a 24fps film. 24 frames of 1080 lines is LESS DATA than 60 frames of 540 lines. Let the box put the redundancy back in if it's needed for 1080i, or output it natively to a TV that supports it. It just makes sense.

    Deinterlacing is more complex with live material shot with HD cameras. Now there is a time differential between each frame, so algorithms have to be applied to prevent moving objects from having a "window blinds" effect. This is why standard definition 480i material looked like absolute garbage when upscaled on early HDTVs. The processing for this has improved a lot over the years.
     
  16. P Smith

    P Smith Mr. FixAnything

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    It's only true for SOURCE !

    Measuring Dish/DTV streamed 1080p24 channels [VOD/DOD/etc] we clearly see highest birate ie MORE DATA then any other 1080i movie.
    Now we could talk ad nauseum about HD-Lite ;) !
     
  17. harsh

    harsh Beware the Attack Basset

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    There's a pill for that. ;)
     
  18. Grentz

    Grentz New Member

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    In the end it is easier just to read reviews and look at how TVs handle different source material. Each TV handles all these things a bit differently.
     
  19. cartrivision

    cartrivision Hall Of Fame

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    That's not exactly correct. 1080i is 1080 unique lines, but only half of them are updated every 1/60th of a second.
     

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