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What HD Monitor Resolution to Get?

Discussion in 'DISH™ High Definition Discussion' started by Oompah, Feb 26, 2006.

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  1. Rogueone

    Rogueone Hall Of Fame

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    this might be a fun read too. this is a Faq page for a Panasonic HD camera that appears to be the type your local TV news crew might take into the field
     
  2. olgeezer

    olgeezer Guest

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    The quote seems a bit strange. Help me. I thought 720p was either 30 or 24 frames. And currently 1080i was 60 fields per second. I thought that 3:2 pulldown had to do with scaling of film. Line doubling would cause blurring of images on an interlaced display, so the frames are displayed in fields as such: the first 3 times the second twice, the third 3 times, the fourth twice, and so on until the second is competed with 60fields and 24frames
     
  3. bhenge

    bhenge AllStar

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    Thanks for all the time and effort to explain this stuff and try to get thru my thick skull. I do realize that in a native 1080i system that the display of a frame will be 1080i, not 540, my concern was what the electronics (scalers? interlacers? deinterlacers?) did with the 720p signal before displaying it on a 1080i device, (regardless of how many frames our brains can process). I had always thought that 3:2 (or 2:3) pulldown (or telecine) was the process of converting 24 frame per second film to 60 field per second (30 frames) video and did not realize that it was also used to interlace a 720p signal. Thanks. BTW, a quick look at pulldown can be read at:

    http://en.wikipedia.org/wiki/3:2_pulldown
     
  4. jrb531

    jrb531 Icon

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    Thanks for the more civil response.

    I still have that one burning question in my head if you would:

    Why does my Rear Projection HD set "only" display 480 and 1080i and not 720?

    Surely if what you say is true about all these sets running 1080 as the "real" resolution then any set that can do 1080i can do 720p?

    Why do we not see many 1080p even if the boxes cannot do them? If the resolution is really 1080 and not 540x2 then I see no difficulty having a set paint 1080p - isn't the issue with 1080p more with the tuner and not the set?

    Thanks for your explanation of the current system. Some I knew, some was new to me but these burning questions are still in my mind.

    -JB

    P.S. Some might say that rendering in two passes "is" only doing have the resolution at one time but I guess that is wrong :)
     
  5. olgeezer

    olgeezer Guest

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    That sounds like an RCA. All displays are supposed to display all 18 digital signals. In some cases this calls for some type of conversion. I do recall some RCA sets that were 720p sets that wouldn't display a 720p signal. Talk about strange.
     
  6. tomcrown1

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  7. jrb531

    jrb531 Icon

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    Quote from article:

    Rear projection TVs typically utilize 7" CRT guns, with some of the higher-end models using 9" guns. 7" guns can typically resolve about 700-800 lines of resolution. The high end 9" guns can do upwards of 900 lines. Typical direct view televisions deliver just over 600 lines of resolution. Most RPTVs have at least 30Mhz of video amplifier bandwidth, which is good for just under 720p or 1080i. Better models have upwards of 75Mhz. Most direct view televisions have 20Mhz video amplifiers, with some higher-end units extending above 30MHz.


    Here we go back to what I was saying and got blasted for LOL - At least on Rear Projection HD sets they cannot do a full 1080 in one pass so they must interlace two 540 line passes. Of course I was shot to all hell so I still must be understanding this wrong :)

    -JB

    P.S. My Samsung 1080i set is about three years old so I'm pretty sure it only has 7" guns. Even the 9" guns, according to this article, cannot do 1080.
     
  8. Rogueone

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    well, the 3:2 pulldown I've seen all over likely came from film, I'd say that is correct. It's just that 3:2 happens to also be the ratio it takes to convert a 720 line image into a 1080 line image and back, so I might hve hijacked the term since it seems to fit :) haha. I think I hijacked the term since I hadn't noticed another 3:2 conversion term many places and it seems like it's the same basic concept going on

    (what follows if my 12 year old understanding of this, if things have changed, someone please let me know hehe)
    anyway, if you have a 720 line image, how do you get it into a 1080 line image? It's like digital pictures, or CD with oversampling, and the like. If you take the 720 and triple every pixel you get an image with 2160 lines. Half of 2160 is 1080. (same works for 1280x3=3840/2=1920)So in a digital world, you split the difference in each line. The 'chips' that do all this converting would need to look at pixels 1 & 2, determine if they were identical or not (1&2 will always be identical), then create the 1080 pixel 1 as a duplicate of 1 of them. Then it looks at pixels 3 & 4. 3 will be identical to 1 & 2, but 4 will be identical to 5 & 6, so the 'chip' needs to interpolate (I think that's the term used) the 2 lines, and look at each pixel, and create a new pixel that is split between the two. Then the 3rd pixel is identical to 5 & 6. I'm likely oversimplifying this, but hopefully the general idea is there.

    At least, this has always been my understanding for how digital data is handled thru compression and size changing etc.

    Of course, going the other way, 1080 would get doubled to 2160, then 720 would need to pick off every 3rd pixel. So pixels 1 & 2 are the same, 3 & 4 are the same, 5 & 6 are the same from the 1080 image. 720 would take pixel 1, 4, 7, 10 etc. So right off, it either takes 2 of the 1080 pixels then drops the 3rd, or it would have to create an image of 720 lines, then go back and interpolate every line pair it had just generated into a new line (I doubt they do this, but if they did it would be like the new line 1 is interpolated from 1 & 2, new 2 is 2 & 3, new 3 is 3 & 4). I'm pretty sure, like in photo resizing, the simplest and cleanest method is to simply drop the every third pixel so that all the other pixels are identical to the original.

    so, I'll say clearly, this how I understand digital to work, and it's possible they've changed it over the years and I just never caught the message :) haha but I hope this makes sense and is still accurate. 1080 upconverts the 720 image and keeps 2/3rds of the pixels identical while needing to create 1/3rd of them as likely transitional pixels. 720 when downconverting 1080 simply is a copy of 2 out of every 3 pixels. And the "reasoning" behind this all is, at these resolutions, and normal viewing distances, the human eye can not absolutely detect the changes. it can sort of think it does, or maybe it'll think one is sharper and one softer, but unless you get close enough to "see" the pixels, you shouldn't be able tell.

    Of course, seeing the pixels is actually a problem when viewing LCD and Plasma, as it's not that hard to see the "screen door" effect when a little too close, or the size is a little too big (like my buds 13'x7' projected 720p theatre. you just have to accept the fact you can see the tiny gaps between the lcd's so you can have that large an image haha). CRT has the same issue, but it seems the way the phospurs work, it's much less noticeable until you are much closer to the screen. And this would seem another reason why LCD and Plasma would like to get to 1080 panels as quickly as they can, it'll reduce the screen door look even more :)
     
  9. Rogueone

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    this is the last portion of the post on the 1st page
    phosphurs have to "die out" just about the time they will be hit again by the electron beam. Since we are talking progressive, there would constantly be phosphurs overly lit during each pass if you were using interlace based phosphurs (1/30th a second light time). Keep in mind, there are 3 phosphurs per pixel for CRT (red green blue) and 3 beams. If the first pass lights all 3 phosphurs, and the 2nd pass only lights red, what will you see on the tV? strong red, weaker blue/green mixing to whatever color their percentages of mix makes. not the red you were suppose to see. For a 720/60p signal, the set would have to do 30p in order to not overwrite the phosphurs like that.

    and there is the expense of the electronics it takes to make 720 sweeps per pass instead of the 540 per for the interlaced. With the same phosphur setup, the 720 pass would need to occur in 1/30th a second, while the 2 540's would occur in 1/60th each, or 1/30th for the pair. Since CRT's need to be compatible with the 480i signal, they have to use the 480i phosphurs, and 1080i uses the same phosphurs :) it would simply cost too much extra for the mainstream buyers to make the crt's compatible with 720p and 1080i :)
     
  10. Rogueone

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    haha i just saw that as well :)

    here is the basic CRT stuff from that link
    CRT RESOLUTION
    Cathode ray tubes are completely analog devices, and unlike other display technologies we have discussed, they do not have discretely ad-dressed pixels that de-fine a native resolution. A color CRT has a matrix of red, green and blue phosphor dots, while a monochrome CRT has a continuous coating of a single [nom-inally] white phosphor over the entire screen. The resolution capability of a given color CRT depends on a number of factors-some of the important ones being the dot pitch (the distance between dot centers, which effectively defines the size of the dots themselves), how tightly the electron beam is focused and the electron beam's scanning speed. A phosphor dot is not a discrete pixel; the sweeping electron beam does not uniquely turn each individual dot on and off, as is the case with discrete pixel types of displays. Rather, as the beam scans across the face of the tube, the areas of phosphor that the beam strikes fluoresce with an intensity proportional to the beam's instantaneous amplitude. The size of the phosphor area illuminated by the beam depends on the focus of the electron beam and the distance between adjacent dots of the same color. If the electron beam is sufficiently well-focused, the tube will be able to resolve an area smaller than a single dot: We may think of a dot as a tiny area of continuous phosphor. If the electron beam's focus is sufficiently diffuse, on the other hand, it may simultaneously illuminate more than a single dot. The dot pitch plays a significant role in determining a color CRT's resolution capability, because it determines the distance between adjacent dots of the same color. If we consider just red dots, for example, one red dot is not directly adjacent to another red dot. There are, rather, green and blue dots that are to some degree positioned between the two red dots. The result is a gap between adjacent red dots, and the size of this gap influences the attainable resolution. The farther apart the red dots, for example, the less red resolution the screen is capable of displaying, and likewise for the green and blue dots. The smallest dot pitch found in a typical top-quality monitor tube is about 0.22 mm, or about 4.45 dots per millimeter, which is about 115 dots per inch. Such a display with a width of 36 inches has about 4,156 dots in a horizontal line. It is safe to say that it is possible for a CRT monitor to display the resolution of HDTV, either 1280 x 720 or 1980 x 1020, if the proper conditions of dot pitch, electron beam focus and scanning speed are met. It must also be pointed out that many CRTs, sometimes even those found in nominally HDTV displays, are not capable of displaying a resolution of 1920 x 1080.

    Then it concludes with this about Projection TV CRTs:
    CRT projectors are subject to the conditions and caveats enumerated above for direct-view CRTs, with the recognition that the tubes used for projection are smaller than those used for direct view. Projector CRTs have round imaging screens, and are monochrome tubes with a continuous phosphor coating across the screen, not phosphor dots separated by a shadow mask. CRT projectors have resolutions up to 1920 x 1080, but it should be noted that they are scanned at 1080i.

    I can't believe this didn't dawn on me before this clearly. A Direct view TV is greatly limited by it's "shadow mask". This mask is there to align the 3 beams onto specific phospur areas. The mask does create a maximum resolution, while not a "native" one. But, with projection sets, there are 3 CRT's each a single color. As explained, those CRTs don't need a mask, and the only limiting factors to resolution are the size of the individual phosphurs, the beam size and the speed it can draw. With our 1080i tv's, beam speed isn't an issue, it only has to go fast enough for 540 lines per pass, and considering these units are "1080" line sets, they do have to have beams tight enough and phosphurs small enough to allow for 1080 lines. Since it's only 1 color each, as noted, that isn't all that hard.


    I've seen and heard that 800 line limit many times and never understood where it comes from. now i think I do. It's either based on old technology before HDTV became mainstream, or that limit comes into play for a 7" crt if it is a 3 color tube with a mask. Dot pitch is obviously an issue with single tube sets, but dot pitch is nonexistant for 3 tube sets :) This is another example of bad information being propogated by many people to the point it becomes fact and no one any longer remembers where the concept originated. If indeed these 7" crt were limited to 700 lines or so, wouldn't they just have made them 720p sets? if you sold a TV as 1080 line capable and it could only do 800, you would very shortly be involved in a class action suit. too many techie people out there would jump on the lie if that were the case.
     
  11. harsh

    harsh Beware the Attack Basset

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    With respect to NTSC video, the article is correct. This is one of the unfortunate compromises of "crystal clear" digital television. Digital television at the SD level is strictly for the benefit of the delivery company and the viewer gets something that, at its worst, appears to be half the frame rate.

    I can remember the first time I saw a live shot with a brand new digital ENG camera on the "local" evening news. Being from Oregon, it was raining. I will always remember how distracting it was to see the rain drops stop and start further down the screen. The waterfalls are a lot less restful to watch in digital.

    There is a reason that HDTV demos typically avoid waterfalls and fountains.
     
  12. Rogueone

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    haha. interesting harsh :)

    yeah, one of those articles mentioned how the old cameras recorded in interlaced as well, so I can see where in a case like that, a 1080i set wouldn't look overly good, and why some still think it's 540 in reality. Because, with the wrong camera, it would technically be 60 different frames ;) but thankfully there aren't gonna too many of those around anymore

    after all this conversing, I feel better about my rptv, but still hate the damn issues with convergence and edge focus :( If not for the cost I'd just replace the damn thing with a dlp and be happy, especially one of the newer 1080p models. but I just don't have that kind of money to burn, so I'm gonna ride this sucker to it's death!! haha still 1 or 2 years on the 5 yr warranty so that helps too
     
  13. jrb531

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    Funny you mention that LOL

    I've gotten so good at manual focus that I can do it in about 30 seconds :)

    The old Samsung auto focus never worked after a tech replaced one of the guns that put me back $300 - a few weeks past the 1 year warranty. Why oh why did I not get the extended 3 year warranty... oh wait I rem... it was $350 for 3 years LOL.... I guess they got my $300 from me one way or another :)

    -JB
     
  14. Rogueone

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    hahaha. I do miss the old NEC convergence menus I used to use. Back in the 90's I installed NEC 3 gun projectors in places like NIH and the CIA and some Navy conference room in Crystal City (2 in that one, cool place). And I needed to converge it for each video type so it could store the settings.

    It would take 4 to 8 hours to get perfect, I liked it to be perfect. But unlike this stupid Mitsu, that sucker allowed you to adjust every cross point and every type of skew, keystone etc. Oh, and I could focus the lenses as well, but then again, the rptv doesn't have variable distances from it's screen hehe

    what i find bad with my mitsu the most are the corners. i just can't get them perfectly adjusted as it doesn't allow manual manipulation there. thankfully most shows are forgiving, but football is funny because I've gotten the lines across the top and bottom out of whack a little, and there is a wavy affect to the screen that is most notable when the field is shot from the side so the lines run vertically the width of the image :) too lazy to get into that secret menu and redo it all. and Sears hasn't a clue how to fix what I've messed up haha
     
  15. Antknee

    Antknee Legend

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    I recently bought a 50" plasma. What I have realized is that you have to take a look at what HD sources you have available and how much you will actually watch. For me, even with Dish HD pack, there isn't much stuff I really want to watch; after the initial coolness factor of HD wears off.
    If you live in a big market and can receive OTA HD or sat HD locals, great. But if you can't or mainly watch SD channels such as History, Sci-Fi, etc. You will be better off going with a smaller set, maybe 42", and maybe even EDTV.
    Why EDTV? Because it's resolution more closely matches SD programming and even DVD. Keep in mind that DVD is not an HD source. SD programming is notorious for looking bad on HDTV sets, especially on larger sets. Most reviews say that EDTV looks great and it is hard to tell the difference unless the sets are side by side and viewing high rez HD.
    In a few years when HD is more prevelant you can buy a brand new HD set. Also, maybe the resolutions will be more standardized. And you will have the EDTV as a nice second set.
     
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