DVD material on standard RPTV vs. HD RPTV

Discussion in 'Archived Threads 2001-2004' started by Brian Dobbs, Jul 25, 2002.

  1. Brian Dobbs

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    Sorry if this sounds like a stupid question, but can somebody please tell me the reason why the picture from a DVD would look better on a RP HDTV than it would on a standard RP? For some reason I can't figure out what the fundamental reasoning is as to why the picture would look better on a HDTV. If the resolution is the same (480i), and without factoring in progressive scan, can someone explain to me what the general reasons are? Why can I visably see the scan lines on my standard RP TV, but I can't seem to see them when I stare closely into a HDTV showing DVD source material without progressive scan involved?

    Thanks in advance!
     
  2. ChrisBurch

    ChrisBurch Auditioning

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    its because the tv has a line doubler.
     
  3. Brian Dobbs

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    Do all HDTVs have line doublers? Can you tell me exactly how line doubling works?
     
  4. Mike I

    Mike I Supporting Actor

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    On an analog tv you have 480 lines interlaced or everyother line being shown at any one time..With an HD set, DVDs will be 480 lines progressive or all 480 lines shown at the same time..Much crisper, clearer picture with not scan lines..Go with a progressive scan DVD player with that HD set and get even a better picture than the sets internal line doubler..Either way the difference in picture quality on dvd between an HD ready set and analog will be like day and night.
     
  5. Brian Dobbs

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    So what you're saying is that every HDTV automatically upconverts the 480i signal to a 480p signal by using it's internal line doubler? Is that the reason why I can't see the scan lines, because of line doubling? Sorry for asking so many questions, but I'm just trying to understand the basics here. Thanks for the replies!
     
  6. Craig

    Craig Second Unit

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    You also have the ability to see anamorphic/enhanced DVDs without downconversion on RP HDTVs. Add in the ability to display a progressive scan signal and you have two factors that make a noticable difference in picture quality.
     
  7. Jan Strnad

    Jan Strnad Screenwriter

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    Brian,

    Yes, that is correct. The HD RPTV de-interlaces (line doubles) the 480i signal, so you see no scan lines.

    Jan
     
  8. Bob McElfresh

    Bob McElfresh Producer

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    Brian: the terms are confusing.

    Your computer monitor is a "progressive scan" or "natural-order" display. The rows of video are drawn in natural sequence: 1,2,3... This is why you dont see scan lines.

    Your ordinary TV is a interlace device. The rows of video are drawn with all the odd rows first: 1,3,5,7,.., then the beam goes up and fills in the even rows: 2,4,6,8,... But the brightness of the odd-rows fades a bit. The scan lines appear when a fresh row of video is drawn in between 2 older rows that have had time to fade a bit.

    There is still a lack-of-standards for HDTV. Most sets have to be able to take any one of these signals:

    480i - (480 rows, interlace - ordinary TV signals)
    480p - (480 rows, progressive)
    540p/i
    720p/i
    1080i

    It's very hard/expensive to build a TV that can take each of these and display them exactly as intended. So most HDTV's accept all of these, but do an internal conversion through the line-doubler circuits to convert everything to something like:

    540p
    1080i

    This makes the display circuits a lot simpler.

    Hope this helps.
     
  9. Brian Dobbs

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    Wow, thanks for all of the great responses guys, I'm really learning a lot! So do all computer monitors display a non-interlaced signal? Why did they even have interlaced when non-interlaced is clearly better? Is it possible to hook up a composite connection to a monitor somehow?
     
  10. Warner

    Warner Agent

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    This is my first post but I've been lurking for a while. Sony DRC actually displays 480p as 960i in order to reduce the visibilty of scan lines. I assume other line doublers do a similar thing. Wouldn't simply displaying 480p instead of 480i make the image more "stable", all 480 lines displayed at once, but still leave you with the same number of scan lines?
     
  11. Jeffrey R

    Jeffrey R Stunt Coordinator

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  12. Warner

    Warner Agent

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    Oops, sorry. Yes, you're right of course, 480p signals bypass DRC. With 480i sgnals DRC interpolates the data to create the information necessary to double the scan lines. However, 480p signals already have double the information and are sent directly to the multi-image-driver circuitry and are displayed as 960i.

    It makes sense if you think about it. Displaying 480p instead of 480i would not reduce the visibility of scan lines, they both have 480. I bet all HD sets upconvert 480p siganls, I know the new JVC sets display everything as 1080i. Toshiba and Hitachi probably display 1080i also, not 540p.
     
  13. Jack Briggs

    Jack Briggs Executive Producer

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  14. Warner

    Warner Agent

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    I'd like to add that progressive scan in and of itself is not better than interlaced. What makes 480p better than 480i is that twice the information regarding the image is available in the same amount of time. It's the additional image information which is better, not the fact that it is in a progressive format. Given a set limititation to display a specific amount of image information in a specific period of time, interlaced is better. Would you rather watch 240p or 480i? How about 540p or 1080i? Interlacing is a great "trick" that provides more image detail given the same "bandwidth", and is better without a doubt.
     
  15. John Royster

    John Royster Screenwriter

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  16. Warner

    Warner Agent

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  17. Allan Jayne

    Allan Jayne Cinematographer

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    >>> Why can I visably see the scan lines on my standard RP TV, but I can't seem to see them when I stare closely into a HDTV showing DVD source material ...?
    In addition, today's interlacing (equals 1950's video) draws each scan line once every 1/30'th (approx) per second and today's progressive scan draws each scan line twice as often (once every 1/60'th second for NTSC). In the former case the odd scan lines have faded significantly while the even scan lines are being drawn, thus you are seeing gaps between odd scan line or gaps between even scan lines, which are wider gaps than gaps between adjacent scan lines.
    Incidentally interlaced scanning was invented because otherwise the top of the screen would fade as the bottom was being drawn, resulting in an even more objectionable flicker, given the limited technology back in the 1950's, and the limited TV channel bandwidth.
    There were interlaced PC monitors at one time. PC technology went to non-interlaced (progressive scan) quickly because PC screens gave more people headaches with interlaced scanning at 30 (or more commonly 43) complete frames per second. Nowadays 70 or 80 complete frames per second are sometimes used because some people notice flicker at 60 frames per second.
    Although DVD has only enough material for 480i, most HDTV ready TV sets double all incoming 480i so only one speed scanning 540p/1080i (and/or also 480p which is very close) of the picture tube is needed. This reduces problems with geometry and convergence.
    Video hints:
    http://members.aol.com/ajaynejr/video.htm
     
  18. Jan Strnad

    Jan Strnad Screenwriter

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  19. Warner

    Warner Agent

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    At least it seems everyone agrees that most HD sets only have one scan rate in order to simplify things and keep costs down. Tell me if you think I'm beating a dead horse and I'll leave it alone [​IMG]
    My info regarding the fact the Sony HD sets display 480p as 960i was from postings on another forum by a guy who trains Sony techs. The Sonys always scan at 1080i, 480i and 480p get converted to 960i, which is inserted into the middle of the 1080 lines by the MID circuitry leaving 120 unused lines. Vertical size is then increased to move the lines with no video information into the overscan area. This method allows for one scan rate and keeps the conversion simple. 480i is line-doubled by DRC, 480p bypasses DRC and is simply converted to 960i by the MID circuitry. 1080i is displayed as 1080i.
    The tv scan rate is its limitation, so I feel that my contention that interlaced is better than progressive given the same scan rate is valid. Everyone believes that 240p would look bad compared to 480i, why is it so hard to believe that it is better to display 480p as 960i? Think of the implications if you believe that an HD set displays 1080i as 1080i, yet displays 480p as 480p or 540p. OK, 540p and 1080i would have the same scan rate, but with 540p the set must double the size of each scan line compared to 1080i in order to fill the screen with no gaps, and that just does not happen. The reason you can't see scan lines as easily on an HD set is because there are more scan lines and hence they are smaller.
     
  20. Brian Dobbs

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    So Warner is saying that HDTV's display a 480p signal as 960i? I'm confused. If that's true, then when would I ever be able to see a pure 480p signal? And when HDTVs upconvert the 480i and/or 480p to 960i, does this mean that they display every line of resolution twice? Is that what line doubling means? I don't understand this forum's general consensus on this issue, but thanks for all the information.
     

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