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  • #16
    Originally posted by tnedator View Post

    I did a google and found some images that show how interlacing works.



    So, the above shows how interlaced (480i sd or 1080i HD) works.
    One point of clarification I realized touched on, but might not have been completely clear on. With modern HD sets, all images are ALWAYS displayed progressive, meaning when there is an interlaced signal like 1080i, the TV set or Cable box ALWAYS converts that to a 1080p or 720p signal.

    Where the potential is for the 1080i signal to look worse than 720p, comes in the converting or deinterlacing. Some TVs and cable boxes have good deinterlacers, many do not. Some times consumers choose to have the wrong unit (TV vs. Cable box or vice versa) do the scaling and deinterlacing.

    Bottom line, both 720p and 1080i look very good. Both 720p and the higher resolution 1080p TV sets typically look very good (although higher resolution doesn't always mean better if it is a poor/cheap TV design) and most TV watchers could never even tell the difference between signals.
    The human body has two ends on it: one to create with and one to sit on. Sometimes people get their ends reversed. When this happens they need a kick in the seat of the pants. --- Theodore Roosevelt

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    • #17
      Originally posted by tnedator View Post
      One point of clarification I realized touched on, but might not have been completely clear on. With modern HD sets, all images are ALWAYS displayed progressive, meaning when there is an interlaced signal like 1080i, the TV set or Cable box ALWAYS converts that to a 1080p or 720p signal.

      Where the potential is for the 1080i signal to look worse than 720p, comes in the converting or deinterlacing. Some TVs and cable boxes have good deinterlacers, many do not. Some times consumers choose to have the wrong unit (TV vs. Cable box or vice versa) do the scaling and deinterlacing.

      Bottom line, both 720p and 1080i look very good. Both 720p and the higher resolution 1080p TV sets typically look very good (although higher resolution doesn't always mean better if it is a poor/cheap TV design) and most TV watchers could never even tell the difference between signals.
      Doesnt the 1080p go to 1080i

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      • #18
        Originally posted by Nick Budris View Post
        Doesnt the 1080p go to 1080i
        HD TV sets have resolutions of 1080p or 720p.

        HDTV signals are either 720p or 1080i.

        TVs have scalers/deinterlacers (converters) that will convert either 720p or 1080i into the resolution of the TV (1080p or 720p).

        In the case of 1080i going to 1080p, in 'theory' what should happen is there should be a slight 1/60th of a second before the image appears and the TV should hold the odd lines in memory from the first interlaced frame, and then when the second interlaced frame comes through, it would blend or stitch them together and display a progressive (the p in 720p) image. However, many TVs still use the old method of 'line doubling" where they take all the odd lines and interpolate (fancy word for a computer guessing) what the even lines 'should' be and display the odd lines and the interpolated even lines, and then the next frame would be all the actual even lines and interpolated odd lines, and so on.

        As time goes by, the equipment gets better, and the results of the deinterlacing improves, but only a 1080p signal (no HDTV broadcasts are currently 1080p) could be displayed on a 1080p TV without having to do some type of signal conversion.
        The human body has two ends on it: one to create with and one to sit on. Sometimes people get their ends reversed. When this happens they need a kick in the seat of the pants. --- Theodore Roosevelt

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        • #19
          Hey, thanks Reid, 69, NB, and tned. I will check this out sometime tonight.

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          • #20
            Originally posted by tnedator View Post
            HD TV sets have resolutions of 1080p or 720p.

            HDTV signals are either 720p or 1080i.

            TVs have scalers/deinterlacers (converters) that will convert either 720p or 1080i into the resolution of the TV (1080p or 720p).

            In the case of 1080i going to 1080p, in 'theory' what should happen is there should be a slight 1/60th of a second before the image appears and the TV should hold the odd lines in memory from the first interlaced frame, and then when the second interlaced frame comes through, it would blend or stitch them together and display a progressive (the p in 720p) image. However, many TVs still use the old method of 'line doubling" where they take all the odd lines and interpolate (fancy word for a computer guessing) what the even lines 'should' be and display the odd lines and the interpolated even lines, and then the next frame would be all the actual even lines and interpolated odd lines, and so on.

            As time goes by, the equipment gets better, and the results of the deinterlacing improves, but only a 1080p signal (no HDTV broadcasts are currently 1080p) could be displayed on a 1080p TV without having to do some type of signal conversion.
            That's what I thought... so there is no HD signal @ 1080 P only 1080 i. Because I have a 1080 P tv but on status it always shows running in 1080 I. Makes sense.

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            • #21
              Originally posted by Nick Budris View Post
              That's what I thought... so there is no HD signal @ 1080 P only 1080 i. Because I have a 1080 P tv but on status it always shows running in 1080 I. Makes sense.
              Exactly. I think the PS3 and Blu-Ray DVDs might be sending a 1080p signal, or at least the hardware can support it for future. However, to the best of my knowledge, Blu Ray is the only 1080p source currently available.

              Not only do no channels broadcast in 1080p, but from what I have read, some of the older 1080p TVs didn't even support a 1080p signal. This means that while the native resolution of the TV was 1080p (1080 lines of resolution, or thinking in PC terms 1920x1080), the TVs circuitry wouldn't even recognize a 1080p signal as vallid if it was to receive one. I assume this was do to the fact that broadcast signals were only planned for 720p and 1080i, but that is purely a guess on my part.
              The human body has two ends on it: one to create with and one to sit on. Sometimes people get their ends reversed. When this happens they need a kick in the seat of the pants. --- Theodore Roosevelt

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              • #22
                Here is a very good write up that explains the differences between 1080i and 720p and explains why 720p is actually better for fast moving, sports action:

                The Facts and Fiction of 1080p
                By: César A. Berardini - "Cesar"
                April 17th, 2006
                Why 720p is better than 1080i in HDTV

                What is better, 720p or 1080i? This has been a topic of discussion for a long time. If only taking into account the technical aspects, the answer is simple. 720p is better than 1080i. The reason?

                Although 1080i has 1080 lines of vertical resolution (against 720 lines of 720p) and 1920 pixels (against the 1280 pixels of 720p) per line, the fact that 1080i is interlaced, causes an overall lower resolution (in practice) than 720p.

                This may seem like an outlandish comment, but keep with me. How can a 1920x1080 signal have a lower resolution than 1280x720 one? Again, the interlaced signal is the reason and that is why I stated “in practice” in the previous paragraph.

                Although there’s a 720p30 format, TV stations broadcast 720p HDTV in its highest variant (720p60), delivering images with a 1280x720 resolution at a rate of 60 frames per second. That is why we said previously that the typical abbreviations used by most are too simplistic and fail to paint the entire picture.

                Here’s the deal. Like I mentioned above, the horizontals pixels (1280 in 720p and 1920 in 1080i) are really pixels per active line and when the interlacing process breaks the 1920x1080 image into two fields, the amount of horizontal lines per field is reduced to 540. As a result the vertical resolution of the field is also reduced to half the initial resolution of the image (frame). In the case of a 1080i signal, the resolution drops from 2 megapixels of a 1920x1080 frame to 1 megapixel in a 540i field. As a matter of a fact, it is because of this that many detractors of 1080i have proposed to call the format “540i”.

                But the key to all the discussions is to never forget that we are not looking at a static image, but instead at moving images that create the illusion of motion. For that reason it’s not the resolution of each image that really matters, but the pixels per second we watch - also known as “temporal resolution”.

                When you do the math, you see that 1080i60 (and also 1080p30) only delivers 12% more pixels per second than 720p60. This is why most people can’t tell the difference between 1080i and 720p broadcasting - because their eyes and brain are practically seeing the same number of pixels per second.

                Code:
                Format	Number of Lines	Pixels per active line	Display Rate		Pixels per second	   
                1080i60	1080		1920			60 fields per sec	62.208.000	   
                720p60	720		1280			60 frames per sec	55.296.000
                Only when static images or small changes in the scene are displayed is that the improvement of 1080i over 720p in HDTV broadcasting is noticeable. As soon you focus on fast moving visuals, 720p looks as good as, or better, than 1080i. This is why it is the preferred format for broadcasting sports.

                In addition, you also have to consider the fact that progressive is better than interlaced. First, progressive scanning will never produce flickering for the viewer, and in addition, there is no need of a deinterlacing process. On the contrary, interlaced signals always require a deinterlacing process at some point, either by the broadcaster or the viewer.

                Another reason why 720 looks better than 1080 in HDTV is because the 1080-line formats that can offer better temporal resolution than 720 are not part of the standard. Although the ATSC includes 1080p formats, they are capped at 24 and 30 frames per second; so there are neither 1080p50 nor 1080p60 variants, which are the only 1080-line formats that will (in practice) surpass 720p60.

                The reason for that is that 1080p50 and 1080p60 would exceed the 19Mbit/s bandwidth allotted in a 6Mhz channel as required by the ATSC standard. The highest HDTV formats that don’t exceed that limit (and in fact are very close to it) are 720p60, 1080p30 and 1080i60.

                To sum things up regarding this topic, the ATSC only allows 1080p broadcasting at a maximum frame rate of 30 frames per second due to bandwidth requirements. 720p video can go up to 60 frames per second with the same bandwidth. 1080 line formats can only deliver a maximum of 60 fields per second (1080i60) or 30 frames per second (1080p30). Both 720 and 1080 line formats, as implemented in ATSC broadcasting, deliver practically the same amount of pixels per second.

                Conclusion: 720p is better than 1080i in HDTV because the highest 1080 line formats (1080i60 and 1080p30) as defined in the ATSC standard, deliver only a few more pixels per second than the highest 720p variant (720p60).

                1080i delivers a higher quality visual when static images are broadcasted. As soon as you have fast changes in the visuals, 720p look as good or better than 1080i.
                http://editorials.teamxbox.com/xbox/...n-of-1080p/p2/
                The human body has two ends on it: one to create with and one to sit on. Sometimes people get their ends reversed. When this happens they need a kick in the seat of the pants. --- Theodore Roosevelt

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                • #23
                  ESPNHD is frickin' amazing. I love watching us on MNF.

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