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How bad is ALiS interlacing? flicker? PAL?

Discussion in 'Plasma TVs' started by sub, Aug 13, 2003.

  1. sub

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    I'm just about to purchase my first Plasma. I'm currently looking at getting Fujitsu P42HHA10 (ALiS 1024x1024), because I can get it at a very good price through a friend. I decided to pick this over the lower resolution P42VHA10 (853x480) because I will occasionaly use my Home Theatre PC to browse the net, and I think the extra resolution will help. I'm also hopeful that HD will make it to my part of the world (New Zealand) some time soon.

    The one thing that concerns me is that the ALiS displays are interlaced. This gives me the ****s! Will it flicker like a PC plugged into a regular CRT TV? or is that not the case with Plasma? I really want a solid picture.

    Also what display (1024x1024 or 853x480) would be better at displaying 576 line PAL content, dvd etc?
     
  2. Blu-rayx

    Blu-rayx
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    sub

    No flicker,Steady as a rock :smashin:



    dvd :cool:
     
  3. tbrar

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    Although both interlaced displays, ie an entire frame of picture information is displayed as two seperate feilds, there is a difference between ALiS Interlaced plasma's and traditional CRT's.

    Traditionally interlaced CRT's work by scanning horizontally every line of picture information in a feild (two feilds making a frame). This is done one 'scan line' at a time, completing a feild within the particular refresh rate, before completing the next feild in the same way.

    ALiS panels although still displaying two feilds in an interlaced manner, display all the lines within the feild in one go - no scanning. That is all the odd lines first feild, then all the lines in the second feild.

    This (as most things with plasma!) is subjective. Both will downscale the 576 lines of resolution to display. You will loose less of the intended lines with an ALiS Panel as at any given refesh rate it will display 512 lines, compared to 480 lines on a prgressive panel. However to some the progressive picture will still be better.

    I think once theory/specs have been compared, you need to have a viewing of the two panels with sources you intend watching and make a final opinion based on what you think is best.
     
  4. vonhosen

    vonhosen
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    ALIS screens just do the processing differently

    Your 576 will be scaled to 512 lines on the ALIS screen & to 480 lines on the 853x480 screen

    Edit
    Oops.....someone hit the key before me:D
     
  5. eMonk

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    tbrar & vonhosen are both wrong - the ALIS panel will UP-sample the 576i to 1024i, the VHA10 will DOWN-sample to 480p i.e. each 288-line field becomes 512-lines on the ALIS. Whereas the two 288-line fields are combined into one 576-line frame and down-sampled to 480.

    Oh, and you can see the flicker on a PC input. I agree that TV/DVD is pretty stable, but if you run a 1024x768 PC output through it, you can definitely discern flicker on high-contrast horizontal lines. 800x600 seems OK though. Ideal resolution is probably 1024x512 (flicker-wise that is) if you can persuade your GFX card to do it. The flicker isn't anywhere near as bad as you get with a PC on a normal TV though. Note that 1024x512 is still more than 853x480. If you really want PC input you should probably consider the Pioneers (1024x768 progressive). One thing to note is that neither the Pio nor ALIS panels have 16:9 square pixels - 853x480 on the other hand is. If you have a HTPC that can drive a resolution of 853x480 you will have the correct aspect ratio. Either that, or live with a slightly squished image. It ought to be possible (theoretically) to get the PC to compensate for the aspect ratio, but I haven't yet tried myself. Of course, you could always drive the ALIS/Pio panels at 853x480 or, say 910x512 (ALIS) or 1024x576 (Pio/ALIS?) and let the plasma scale the image. Note to the fussy: I'm not suggesting that is necessarily a good idea, and will depend on the scaling abilities of the plasma's electronics.

    I might try those resolutions out actually - up to now I've only connected my laptop (which only supports the standard VESA/XGA resolutions), I may drag my PC through from the other room and see what happens.

    Definitely agree with tbrar that you should never listen to the people on this board (or the magazines for that matter), above the rating abilities of your own eyes.
     
  6. tbrar

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    Emonk,

    As far as I understand, the procedure a ALiS panel goes through when fed an interlaced source is:-

    1. 576i is converted to 576p
    2. 576p is upscaled to 1024p
    3. 1024p is converted to 1024i and displayed as such, 2 fields of 512.

    If fed a progressive source, step one is by passed.

    Now the above is how ALiS works, as such you are loosing picture information as we stated.

    Have a look at a thread on this very forum called 'Plasma Resolutution Again'.

    Also have a look at www.avsforum.com; The, What is ALIS Question ? on the Plasma FAQ.
     
  7. eMonk

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    from the avs faq:
    480i: each field is upconverted to 512 rows,

    Note that "field" means 240 lines.

    I assume 576i is similar.

    In what sense are you losing information then?
     
  8. tbrar

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    Emonk,

    576 x 2 = 1152, not 1024 (2 x 512 feilds). It is in that sense that you loose information.

    Below is a quote from a Hitachi Engineer answering a question I posed when I had a 42PD3000:-

    Tony
     
  9. eMonk

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    576 x 2 = 1152, not 1024 (2 x 512 feilds). It is in that sense that you loose information.

    that's 576i
    i.e. 288x2 there are NOT 1152 lines of resolution in ANY consumer video standard of which I am aware.
     
  10. tbrar

    tbrar
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    EMonk,

    I am not saying that there is.

    My point is to do with what happens to the interlaced signal, or indeed progressive input, the process involved as hopefully the quote showed.

    In that each feild is not upconverted, rather changed to progressive, upscaled, then converted back to interlaced (2 x 512) prior to display.


    Tony
     
  11. eMonk

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    each pair of 288-line fields are recombined into one single 576 line frame (i.e. the same thing that Arcam do in the 88+ or Denon in the 2900 etc - no loss of information correct?). this is then up-sampled to 1024 lines (no loss of information yes?).

    This 1024-line image is then split into 2 512-line fields and displayed. Now this being interlaced is not ideal but again there is no loss of information.

    Now, your progressive Pioneer will take the 2 288-line fields and combine them into a single 576-line frame then up-sample to 768 lines and display. Again no loss of information. The difference is simply that instead of displaying half of the lines for 1/50th of a second then the other half for 1/50th, the Pioneer displays all of them for 1/25th of a second.

    A display of 480 lines will take the two fields, combine into one frame the down-sample and display for 1/25th of a second. Hence it loses information.

    Whilst technically, I agree that the Pioneer 433HDE/MXE is better than the ALIS panel, having > PAL resolution and being progressive, the ALIS is still > PAL, and for my money had the edge in picture terms. Again, the Panasonic I think probably had the best PQ but I could see the flicker, which totally detroyed it for me. If only Panasonic would produce a 1280x720 panel that didn't flicker...

    Of course, when I retire my plasma to the bedroom after five or so years trusty service (touch wood) I'll buy a nice 42" plasma (or probably OLED :)) for < £2000 that can display 1920x1080 progressively with no flicker. Mmm...
    :D

    Dunc.
     
  12. elan

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    Good Post E-monk

    It's about time someone posted some correct information re the ALIS panel instead of faulty hypotheses!!
    I cannot believe that people believe that if you take a 576 line (288 lines at once) image upconvert it to 1024 and display 1/2 the lines at once (512) you are some how losing information. there is a net gain of lines every frame.
    You are taking an image which is 288 lines and up converting it to 512 lines a net gain of 134 lines per field.
    In Summary you have taken a 576i image change it to 576P Then to 1024P and then to 1024i, 1024i is an upconversion of 576i anyway you look at it, with no loss of information

    Tbrar - "In that each feild is not upconverted, rather changed to progressive, upscaled, then converted back to interlaced (2 x 512) prior to display."

    This is the answer to your question once the picture has been upscaled - even if you divide it into 2 frames the picture has more lines in each frame than the source. The problem you guys have is you think a progressive image has double the image information an interlaced image does this is incorrect. It only shows a solid image for the full time as compared to 2 halves!Unfortunately the human eye can not resolve the two sepeate frames thus it is percieved as 1024 lines.
     
  13. tbrar

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    Guys,

    You are right with respect to an interlaced source, apologies for my confusion !. I think I know where my confusion stemmed from..... birth :)

    However, for progressive sources of say 576p (or 720p) input to the panel. That is 576 lines per 1/50th second for PAL - picture information is lost in the donwconversion process. Is that correct ?.

    Going by AVS Forum it states that for a 720p, each feild is downconverted to 512 rows, it also states that a 720p source is displayed at 1024x512 and finally 'that for progressive sources the resolution that you actually see is 1024X512'.


    Tony
     
  14. eMonk

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    Nope. Wrong again. 576p means 576 lines per 1/25th of a second.
    PAL is PAL is PAL. It only has a certain bandwidth, and that caters for 625 lines every 1/25th of a second, of which 576 are active lines of picture information.

    A progressive scan source is still outputting 288 lines every 1/50th of a second, but instead of it being every other line of the whole frame, it is every line of the first half, then every line of the second half. Hence 25 fps. It's really very simple. As has been said before this simply by-passes the i->p conversion in the ALIS and then gets scaled to 1024p and displayed as 1024i. Still no loss of info. Just interlaced.

    Similarly 720p is 720 lines every 1/25th or 1/30th or potentially 1/24th of a second (whatever). This will get up-sampled to 1024 and interlaced. Once again, this isn't going to be as good as 1024x768 which can display the whole thing but it still ain't losing information.

    I'll state it again. There is no loss of information. ALIS is simply using a slightly inferior display technology that means it will flicker slightly with high-contrast horizontal lines. At least the whole screen doesn't flicker as with the Panasonic. And for those of you who don't notice the flicker on the Panny, I can't imagine you would notice the flicker on an ALIS. I spoke to a sales guy in John Lewis when I was doing some searching, and whilst he thought that the Panny flickered, he thought that the Hitachi 42PD3000 was progressive because the image is so stable.
     
  15. peejay

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    I've read many posts on these boards recently that argued persuasively that ALiS technology resulted in a loss of information, something that put me right off buying the Hitachi. Indeed, it put me right off buying a plasma (because I couldn't stretch to a Pioneer). Thanks for putting the record straight (assuming of course you are right - I hope you are!)

    Now, about the buzzing I've heard people talk about...
    ;-)

    Peter
     
  16. tbrar

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    Guys,

    Been doing a bit more looking into previous.

    Below is a quote from the AVSFORUM, a chap called 'trainerdave'. Now, trainerdave is a director of training for Fujitsu, I would imagine hes fairly knowledgavle about ALiS panels and how they handle sources:-

    Now what trainerdave is saying (if you search for his posts in the AVSForum, there is loads on this very subject), Is that as stated you DO lose lines of resolution feeding the ALiS panel a 720p source. This being the case, what happens with a 576p source?. I think more research is warranted prior to putting this one to bed !!

    Tony
     
  17. eMonk

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    I seem to recall reading somewhere that when fed a 1024x768 PC display, the ALIS panel takes 512 lines from the frame as the first field, then takes the remaining lines as well as some of the previous 512 for the second field. I'd imagine that this would be the same as for 720p HDTV sources. This is just another way of saying that the 720p is scaled to 1024p and then interlaced.

    This would certainly tally with my experiences of using PCs with my plasma. At 800x600 there is very little flicker, but if you get a high-contrast horizontal line at the right point on the display it flickers somewhat. I was reading these forums on my plasma last night for instance, and when scrolled to just the right position on-screen, the post dividing lines would flicker. Oh, and the underline on the link at the top-left "New to home cinema?..." seemed to be at just the right place. I find that 1280x768 is pretty reasonable (and nearly 16:9), there is some scaling done that makes it look fuzzy when close-up but from the sofa it looks better than the 854x480 res that I fed it (nasty blockyness about it). I tried the 910x512 and 1024x576 neither of which worked very well - the display was OK, but tended to lose bits off the side :(.

    Of course the other thing is that this is done by the "tuner" electronics not the panel. You could do it either way, and maybe they do? Hitachi use different electronics for the 42PD3000 and the 400E for Pete's sake, who's to say Fuji don't do something different again?

    As to the buzzing, that's easy to explain... the Hitachi panels are powered by an MPAF (Massively Parallel Array of Flies), these guys are coupled to a piezo-electric generator oh, and the constant flapping of tiny wings allows them to remove the normally noisy fans. :D
     
  18. tbrar

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    Gents,

    I am still unsure, your point taken about Fujitsu/Hitachi having different electronics. However, have a look at the following question posed and subsequent answer:-

    What I think he is stating, going by the previous post and above is in ALiS panels (Hitachi, Fujitsu etc), the 720p source is downscaled to 512 and doubled for display. That is the 720 is downscaled to 512 (loss of picture information). This downscaled source is then doubled for display resolution.

    The origanal source is not simply scaled, it is first downscaled to 512 lines of picture resolution. It is this downscaled picture that is then doubled to make a 1024p signal, finally this is converted to 1024i and displayed as such.

    Therfore for a 720p source you are loosing (720-512=208/720*100) 28.88% of intended picture. I would imagine the same is equally true for a 576p source, apart from it will be (576-512=64/576*100) 11.11% of intended picture.

    This being the case intended picture information is lost when progressive sources >512 resolution are fed into an ALiS panels. However, it is confusing to be honest, so to confirm this I have emailed Trainer Dave and will post if/when have reply.

    Tony
     
  19. Geeseman

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    That's fine, as long as the image is only refreshed at 25 frames per second (PAL, 30 NTSC).
    What happens when you feed it a progressive image at above 25 frames? PC and console do this.
     
  20. tbrar

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    MMmmm......

    Consider, a 576i sources into an ALiS panel. That is two feilds of 288.

    Based upon whats been posted earlier (by reading trainerdave's posts) one school of thought may be:-

    1. The panel takes in the two feilds of 288, combines to make a 576p signal.

    2. This 576p signal, is downscaled to 512p lines of resolution.

    3. This downscaled resolution is then doubled to 1024p, converted back to interlaced and then displayed as such.

    Consequently, will it not follow that you lose lines of resolution with a 576i input aswell ??.
     
  21. peejay

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    trainerdave on avsforum.com (special guest forum) says, about 480i:

    "480i is alternating fields of 240 lines of resolution. so we upconvert each odd field of 240 lines to 512 and show it for a 60th of a second, then go on to the next even field and upconvert its 240 lines to the other 512 rows of pixels."

    I don't think he explicitly answers about 576i, but surely it would be very odd if that was done any differently?

    So is that final on PAL broadcast material? No loss of information?

    Peter
     
  22. tbrar

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    Peejay,

    I agree it would be odd, but I am not so sure any more. I have emailed the chap, but nothing back yet !!.

    The thing thats got me thinking all this is how Trainer Dave states it deals with the 720p source, ie downscales to 512 (number of lines of available resolution at respective refresh rate ie 1/60th or 1/50th second) this is then doubled to make the 1024p, converted to interlaced 1024i, then displayed.

    As all have maintained with interlaced sources the first thing that occurs is the fields are combined to form a progressive frame.

    NTSC broadcast material is 240ix2=480i, this would then be converted to 480p. Here this would be upscaled to 512 (note: upscaled from 480 to 512), then doubled prior to being converted to interlaced and displayed. So it follows you will not loose any information with NTSC.

    With PAL broadcast material it is 288ix2=576i, this becomes 576p. If the same procedure is followed as described previously, this would be downscaled to 512p, then doubled to 1024p, converted back to interlaced and displayed.

    So dont know....... but it is quite interesting trying to find this out :eek:
     
  23. Geeseman

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    Well, 720P is a progressive signal, so it has to be downscaled to 512lines because that's the progressive resolution for the panel.
    720P is refreshed at 60hz (NSTC) and the ALIS panel can only ever display 512 lines at 60hz. Interlacing is not neccessary here.
    As it goes for 720P
    1280 lines vertical are scaled to 1024
    512 lines horizontal are scaled to 512
    Image is displayed at 60hz.
    480P is similar, but it is upscaled somewhat.
    576P is downscaled horizontally, but upscaled vertically.
     
  24. tbrar

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    Geeseman,

    Interlacing is always neccessary as it is an interlaced panel. ALiS are interlaced displays. The panel displays an interlaced picture of 1024 x 1024i, period - regardless of input.

    The discussion here is the mechanics involved in getting to the point of interlaced display. As it is the steps involved that will determine whether or not intended picture information is lost.

    One method states the entire input (720p or 576p, or 576i?) is scaled to 1024p, then converted to 1024i and displayed as such. If this method is correct no intended picture information is lost as the entire input is spread accross the two interlaced feilds of display.

    The other mothod is the input, after conversion to progressive if neccessary, is first downscaled to 512p, this is then doubled to 1024p, then converted to 1024i and displayed. With this method intended picture information is lost, as the panel firstly downscales the input to 512p and spreads this picture information accross its two interlaced feilds of display.

    I am increasingly of the school of thought that the second method is used, definatly for progressive sources >512 vertical resolution (thats horizontal lines counted vertically) and potentially for interlaced sources that have a frame resolution >512i.
     
  25. HDR

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    why do you guys think that it has to downscale to 512. Surely the unit will have a frame buffer capable of holding the full 1024 * 1024 pixels, which it will then output to the display 512 lines at a time _ odd, then even. Where does the need to downscale to 1024*512 come into this?
     
  26. tbrar

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    HDR,

    The downscaling to 512 first is from the posts that this chap called trainerdave from AVSFORUM has posted. trainerdave chap is a director of training at Fujitsu in U.S.

    One of his posts stated :-

    If you look on his posts (search under ALIS and trainerdave) he refers to this method of handling 720p sources. I have Emailed him for claification but he has not replied as yet.

    Its quite confusing as everyones got different ideas of how ALiS actually works, what is displayed with various inputs and the procedure in the panel. So its an effort to deduce a definative answer TBH. Any thoughts ?


    Tony
     
  27. Wayne Moule

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    But at the end of the day,it's what your eyes perceive as being the best picture,as I find the above very very confusing and way over my head.

    The best bet is to see Plasmas in action.
     
  28. Blu-rayx

    Blu-rayx
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    Wayne Moule,

    I totally agree with you :smashin:


    I've got the Hitachi 42 pma400e and the PQ is amazing,so i have no problems with ALiS screens :)


    dvd :cool:
     
  29. tbrar

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    I certainly havn't got anything against ALiS screens. Each to his own and all power to him etc. etc. Everyone has different requirements and tastes, otherwise this wouldnt be much of a forum ! :smashin:

    I think this thread has become informative, if confusing, in trying to finally nail down how they work as everyone seems to have different theories and this seems to be the case on every forum I look at !.
     
  30. Geeseman

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    You guys need to understand that 720P is a video signal, not a PC signal.
    Video signals run at a maximum of 30 frames, so they can be interlaced.
    PC signals run at any frame rate that the monitor can accept, and *always* at a rate above 60 frames, so they are not practical for interlacing
    As the ALIS panel displays each 1024 X 512 field 30 times per second (with 60 X 1024 X 512 fields displayed per second), any signal that is placed into the montor at above 1024 X 512 pixels at a refresh rate of 60 fields per second will have to lose resolution to be displayed.
    That includes SVGA (800 X 600) or anything above. How much data to be lost depends on what is happening to the graphic display between field. If nothing changes (static text for pc windows etc) then you won't notice much of a difference. If you have games (Quake etc), then you will notice it, just like interlacing affects videogame console on TVs.

    As for video signals, it could either form an progressive signal, scale to 1024 pixels and interlace or scale each field up or down to 512 lines and then display...
     

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