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What is the 50hz issue/ What is Dynamic false contouring/ What is Posterizing.

Discussion in 'Plasma TVs' started by Scooby2000, Feb 29, 2012.

  1. Scooby2000

    Scooby2000 Well-Known Member

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    With more and more people asking this in threads I thought it a good idea to start a thread on these topics. Why all in one thread? Well to get rid of some of the confusion over these issues. This thread is open to all, but it would be good to have contributions from tbose who know about these issues. It would also be good to keep the thread quite clean as in no off topic chat. If people have links to useful info I will add them to this post. I know a little about these issues but it would be good to have a more indepth knowledge if those that have it would like to share.;)
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  2. reaper12

    reaper12 Member

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    Great idea, now can somebody answer these questions please? :)
  3. snooper

    snooper Member

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    If someone decides to give the full technical details can they also simplify them in laymans terms as not everybody will have a clue what your going on about.
  4. NBrice

    NBrice Member

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    I've seen many people say that the 50hz issue is not the same as false contouring/posterising.

    This may well be the case, but there was no doubt that my GT30 exhibited a lot of false contouring on 50hz/24hz content, whereas it exhibited very little on 60hz content. This is in Normal, Professional and THX modes.

    It was the false contouring that made me pack it up and send it back to JL. I've had VT30 demos in shops and the problem is there too. I think I may be more sensitive to it than others because I struggle to understand how it can't be a big issue for anyone else. It's on ALL content, filmic 25fps or standard 50fps and I hate it. Looks like everyone's face turns into a 256-colour GIF on fast movements.

    I'm really hoping that the new 50 series panels fix this problem and bring 50hz up to the 60hz standard. Because I would have been more than happy with the set if it wasn't for this issue.

    I don't see this problem at all on Samsung's plasma range but unfortunately they don't go down to the 42" which is my maximum size.
    Last edited: Feb 29, 2012
  5. Insanity202

    Insanity202 Active Member

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    I'll answer one to get the ball rolling.

    Posterization is where skin tones for example lack detail and look more like a cartoon than a person. ;)
  6. Mark Hodgkinson

    Mark Hodgkinson Reviewer & News Writer Staff Member

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    I think the confusion arises because, as the terms are used, the effects can manifest themselves in similar ways, as woodnotes alluded to above.

    50Hz issue - break up of edges under panning, leading to double/treble/sometimes more images. Easy to spot when watching football as the ball travels across boundary lines or, my personal 'favourite', the lights in the background of the BBC Comedy Roadshow. Seems to be more noticeable with medium to fast pans.

    (Dynamic) False Contouring - again often noticeable on the edges of objects but doesn't have to be under panning. Often manifests as green/red 'stripes' on skintones and pale backgrounds. In actual fact, the term false contouring is just an aka for banding/posterization (see below) but it has recently become the accepted term to describe the effect around these parts.

    Posterization aka banding - the inability to show gradients of colour smoothly leading to bands of slightly differing shades. Often noticeable in skyscapes where the blue is split in to bands of slightly different hues of blue. Not always the fault of the display and can be down to the 8 bit source material but more common to plasma than LED/LCD because of the lower bit panels/processing used.

    EDIT: To add Dynamic to False Contouring for clarity.
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    Last edited: Mar 1, 2012
  7. VierraFan

    VierraFan Member

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    To understand explanation, I think that some basic knowledge about how PDP is working would be needed. In short, unlike other technologies, pixels on the plasma screen can have only on or off state. So various intensities of individual red, green and blue subpixels is achieved by switching them on for short periods of time. On modern screens, this is done 600 times per second (called 600 Hz subfield drive). Each pulse is called a subfield. Due to technical limitations, for every subfield all pixels that are 'on' are 'on' for the same period of time (which is of course very short). Usually, time of producing the light is shortest in the first subfield and longest in the last subfield in a group of 10 subfields in case of 60 Hz 'refresh rate' (there are also 50/100 and 48/96)

    However, since this explanation was really brief, I suggest some additional googling for those who didn't study this subject before. Also, I'll try to prepare slow-motion video so you will see how this actually looks like on real TV and not only in theory

    Since we have 10 subfields in a group, and each pixel can be 'on' in various of them, theoretically we have 2 ^ 10 = 1024 posiible levels of each red, greeen or blue subpixel (from darkest to brightest)

    Unfortunately, there is a problem. Everything is fine if you are looking at the same position on the screen. But you are not (subjects are moving or you just want to observe different parts of the screen). In that case, your eye would be summing those pulses differently than it was intended, so some parts of the screen would appear considerably brighter or darker. It is called DYNAMIC FALSE CONTOURING. This problem is even bigger now when we have Full HD screens and pixels are smaller and closer. And we have 3D, where better phosphors are used (shorter decay time). So it seems that manufacturers decided to drastically reduce number of possible combinations. For Pioneer Kuro, it is known that number of combinations was only equal to number of subfields. If you check my thread about dithering, where I treid to record the situation with Panasonic, you would see that it is (or at least it seems to be) quite similar.

    Unfortunately, number of used gradations per color (roughly 10-20) is now too low to display all colors in the video (about 240 levels per color), not to even mention declared 6144 levels, so a dithering technique is used, known as error diffusion. For those familiar with virtual dub editor, browse for error diffusion plugin and play with it (or check a short exposure photo in my dithering thread). This technique is usually producing good results, but unfortunately not always. When it fails, we have banding / posterizing. So these two things are connected, in a way that banding is result of combat against false contouring

    My theory is that issue with 50 Hz mode (some also report 48 Hz mode) is connected with this, as I described in the dithering thread, but can't say for sure without further tests
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    Last edited: Mar 1, 2012
  8. vipergrm

    vipergrm Active Member

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    Superb info guys. Thanks for that!
  9. panman40

    panman40 Well-Known Member

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    Around the time i had my VT20 Posterisation and False Contouring were one and the same issue just diff names :confused::rolleyes:, Either way it had Both :laugh:
  10. Jacksdad999

    Jacksdad999 Active Member

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    My main worry is this - im not sure if what I am seeing is motion problems associated with Panasonic plasmas or all plasma technology. The reason I ask is that hardly any reviews of the gt and vt series mention the problem and those who do say that it is only noticeable on occasion. I see the image doubling up on panning shots and where people move there heads quickly, particularly on film based material. Its almost like its showing the individual frames. From what i have read this doesnt seem to be the same thing as the 50hz bug. I have the opportunity to change to a Samsung d6900 but can't demo it and am worried that the same motion problems will exist on it.
  11. BJQ1972

    BJQ1972 Member

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    Motion on Samsung plasmas is different - you won't see the 50Hz issue or false contouring, but you will still see the occasional doubling on pans, plus the motion resolution is less - so there is more motion blur.
  12. Jacksdad999

    Jacksdad999 Active Member

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    Thanks for that. So do you think I would just be swapping one set of issues fur another. I seem to be quite susceptible to motion issues.
  13. Scooby2000

    Scooby2000 Well-Known Member

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    I had read posterising and false contouring were separate issues:confused: Ill see if I can find where I read it(may take some time) Im alao sure Phil had told me this, though I may be rwmembering wrong. I thought posterizing was a lack of available colours and is effected by the materials bitrate? False countours I thaught was similar but more linked to motion?
    I may be talking arse its been a long few days and my brains all squishy.
    Thanks for the contributions chaps, maybe some links to good info would be an idea, technical as well as laymen, like to get the old grey matter working.:)
  14. Insanity202

    Insanity202 Active Member

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    My advise is go test the Samsungs mate.
    I had the VT30 motion at times with 50hz stuff was shocking, and posterization made folks faces look like cartoons. Even the wife complained (never upset a pregnant lady when shes watching her soaps :nono:).
    The 30 series was the first range (and I think the only plasma tv) that used 1080 lines of motion res yet still suffers with the above issues. Samsung use 900 lines of motion res and imo have better motion.
    On paper Panasonic should out class there rivals with there specs but in reality this doesnt to me seem to be the case.

    If your worried see if you can take a clip of a movie/tv programme you know really well and go demo it on a few tvs. Let your eyes be the judge ;)
  15. Red1

    Red1 Member

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    The recent panny pro-panel review (the 65VX300), says that none of these issues occur, so they can do it.

    Hopefully some of the tech used will be passed down to the 2012 50's or maybe the 2013 60's? :laugh:

    Red1
  16. VierraFan

    VierraFan Member

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    Improvements are possible. They are however connected with production costs. I'm wondering what is 2500 ffd really about in 2012 top models - is it what a brochure by Panasonic suggests, or not really ...
  17. MrBungle2005

    MrBungle2005 Member

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    An interesting read. I had always just assumed the posterisation I had been seeing was down to compression used (Sky HD stuff for example) as I have sometimes seen it in videogames and assumed corners were being cut at the broadcast end.

    I must say though that it hasn't worried me up until now. The 50hz bug however - I'm sure my old PZ80 didn't suffer it as it definitely looked better with our broadcast stuff, though I couldn't put into words exactly why, even with the helpful posts above.
  18. panman40

    panman40 Well-Known Member

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    Thats more than likely correct, just saying at the Time when we were discussing that issue 'back then' we referred to them as much the same thing;).
    Maybe a sticky from a rock solid source explaing what all the issues are with/without pics, ie
    Postersation
    False Contouring
    50hz Bug
    Banding
    Dirty Screen Effect
    Edge Bleed
    Corner Clouding
    Motion Judder
    Motion Blur

    The list could go on and on :laugh:.
  19. VierraFan

    VierraFan Member

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    Of course banding can be already present in the source video, due to compression. However, PDP is sometimes producing banding on (almost) perfectly smooth areas. Problems are usually visible where brightness is changing quickly - dithering method fails because number of pixels on that area is too small, so actual gradation levels are visible. See attached picture (on the left - part of the frame from the 24p movie, on the right, how it looked on the screen)

    Attached Files:

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    Last edited: Mar 1, 2012
  20. Scooby2000

    Scooby2000 Well-Known Member

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    Well volunteered sir, you have a lot of work ahead.:laugh::devil:
  21. deblee

    deblee Member

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    Very interesting post
    I only tend to notice the posterisation/banding on low bitrate stuff mostly.
    I did see some affect on one of the Sky HD channels (can't remember the programme now) but when I recorded it & played it back on my LG plasma and an lcd/laptop the issue was also present on those displays as well so I figured it must have been the broadcast
    I do notice the 50hz bug (football line especially) and I do have problems with occasional medium paced camera movement that shows static objects with green/red blur but on my ST30 its not intrusive for me so far
    Any display tech has issues, I guess its whether those issues bother you
    Last edited: Mar 1, 2012
  22. Chelsea_Fan

    Chelsea_Fan Member

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    To differentiate this effect from regular false contouring the effect you describe above is called Dynamic False Contouring because there has to be movement to initiate the visual effect.

    I think this could be a really useful thread :)

    There's a whole host of issues in our flat panel displays that limit the performance when there is motion. Some is inherent in the MPEG compression used in digital TV broadcasts anyway and some is due to the nature of progressively updated displays.

    When you add in the plasma issues eg dynamic false contouring and dithering you end up with various reasons why the image doesn't look 'right' when there is motion :)
  23. VierraFan

    VierraFan Member

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    You are right, dynamic false contouring (DFC) term is usually used (although word dynamic is sometimes omitted). I attached usual explanation how it can happen. However, it can also happen on statical scene, if point of your focus is moving across the pixels within refresh time. And that point is moving all the time

    Modern plasma televisions are using only combinations that are 'safe', and number of them is much lower than number of all combinations

    Also, it's much more likely that blue color will exhibit DFC, because response time of blue phosphor is very short. Green and red are much slower, so they are producing light between subfields also (as I recorded in dithering thread). Unfortunately, they are leaving yellow trails for the same reason. Quicker the phosphor = less yellow trailing but higher possibility of DFC

    Attached Files:

    • DFC.jpg
      DFC.jpg
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    Last edited: Mar 1, 2012
  24. Scooby2000

    Scooby2000 Well-Known Member

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    Thats my bad, changed the title, bit sloppy on my part.:rolleyes::)
  25. panman40

    panman40 Well-Known Member

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    Just the reason i suggested a Sticky, Banding on a PDP is not neccssarily taken the same way as LCD Banding. This is where Confusion reigns lol. I have had LCD and Plasma tv's for a few years now and its quite amusing how different terms morph into issues with diferent owners :laugh:.
  26. Scooby2000

    Scooby2000 Well-Known Member

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    Well if we can get the information hear I will make a sticky.:) For the sticky though it needs to be nice and simple for people to read, not a wall of text as that may put many off reading. I think a mix of basic description and links to more technical pages would be best. Lets see what you guys can get together. :)
  27. fluxo

    fluxo Active Member

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    However, if you were to observer the pixels over a short enough interval, the
    differences would be less obvious. All displays emit light as discrete packets
    ("photons") and in a very short time interval you will either capture one with
    a detector or you won't. LCDs have no special ability to produce half photons:
    photons are indivisible. In that sense LCD pixels also only have an on or off
    state.
  28. VierraFan

    VierraFan Member

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    Well, it's true I suppose ... however you can't see that light source is emitting individual photons, so I think this isn't important for this discussion, while non-continuous light emission from PDP is causing some problems. But, connected with that, it should be mentioned that light emission from LCD isn't quite continuous, because backlight intensity is regulated by pulse modulation. For instance, my LCD computer monitor has backlight frequency 180 Hz. If I set brightness to maximum, light emission is continuous, otherwise not
  29. lesd57

    lesd57 Member

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    Hi

    Seems as though I am having similar problems with my TV as others. I too get contouring on faces etc when movement is detected. It is annoying especially when you have spent so much on a TV, which came from John Lewis. I have had the TV for about 7 weeks and have been complaining to John Lewis for the last 2 weeks.

    Tried to get hold of Panasonic to discuss but they were as helpful as a chocolate teapot.

    Any suggestions? Is this something that you just have to put up with or is it more noticeable on some VT30's than others?

    Would anyone suggest I return the set to John Lewis and demand a refund? However I will need a new TV so would I get the same with something else?

    Should I consider an LCD/LED instead of a Plasma?
  30. arenaman

    arenaman Moderator

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    I think I'm going to be camped on this thread, I've currently got an escalated complaint at Sky due to the false contouring/posterization that I get ONLY from Sky, this has just started happening in the last couple of months ruining my viewing it's been passed onto their Testing and Product Safety Team (TAPS) as the specialist engineers didn't have a clue how to fix it.

    If the picture had been gash from the start I wouldn't have minded but it's gone from fine to gash overnight. Going against the grain here I can't recall it ever happening on my plasmas but I've tried 3 x separate LED/LCD TVs and it's there every day.

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