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New Panasonic TXP-55VT65 - Posterization |
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#1 |
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Forum Member
Join Date: Mar 2007
Posts: 204
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New Panasonic TXP-55VT65 - Posterization
After shelling out nearly £2,500 on a new 2013 model Panasonic Plasma TV Model TXP-55VT65B which is suppose to have a cracking picture with some 30,260 levels of graduation? then why is it I'm still seeing "Posterization" on sky scenes for example when watching last night's Top Gear on BBC1 in HD?
I would have thought with this number of levels from Black to White, this Posterization would have been a thing of the past? So my question here is actually how many levels do they actually transmit? and was it worth paying this extra premium if the source materiel is this poor? and how many levels do BluRay Disc's support? Is this 30,260 levels a bit of a gimmick I ask myself
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#2 |
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Forum Member
Join Date: Apr 2006
Location: North Derbyshire
Posts: 41,794
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I would imagine it's simply an advertising con?, just like the 600Hz claims.
You need to consider how a plasma TV works, essentially each cell (1/3 of a pixel) contains a little 'explosion', which creates a burst of ultraviolet light, and the phosphors on the front of the screen convert this burst to visible light. This means that Plasma cells can only be either ON or OFF, not very good for a TV ![]() In order to generate a greyscale each cell is fired multiple times, with older plasma sets having only 256 different possibilities - and this limited range is the theoretical maximum, in practice it will be much more restricted depending upon the brightness and contrast settings. The time a single 'firing' takes is presumably fixed by the way it works?, and the number of times you can fire it is limited by how long it remains on the screen - for a 50Hz set that would be only 20mS, and for a 100Hz set (which the 600Hz ones actually are) only 10mS. So you presumably can't make the 'firings' shorter, and can't extend the number of times you fire them, so either Panasonic have done something exceptionally 'clever' (but apparently not by your observations) or the marketing boys have stretched the truth a little. My old Plasma obviously does it,and you just get to ignore it (my wife has never commented on it, and I've purposely never pointed it out) - I'd presumed modern Plasma's were less susceptible to the problem though?. |
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#3 |
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Join Date: Sep 2004
Posts: 14,718
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Quote:
So you presumably can't make the 'firings' shorter, and can't extend the number of times you fire them, so either Panasonic have done something exceptionally 'clever' (but apparently not by your observations) or the marketing boys have stretched the truth a little.
. Or they may have stretched the truth a little, I'm in no position to know. |
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#4 |
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Forum Member
Join Date: Jun 2003
Location: Cheshire
Posts: 6,462
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Regardless of how many grey shades a screen can display, all video information for TV and DVD/BD is based on 8 bit per channel (24 bit for the three channels combined). That's 256 theoretical shades per primary colour. But we don't use the full range. Video uses a truncated range.
Out of the 0-255 maximum number of shades per colour, video uses a smaller range of 16~235 (219 shades per colour). It's slightly more complicated than that though because we don't see blue in as much detail as green and red, so the blue channel bit depth is reduced and the capacity is shifted over to the red/green channels. What this all means is that the source data is limited in colour depth. So even with a display with infinite grey shades there'll still be colour gradations because it's in the source data. Clever interpolation can help minimise the impact, but sooner or later there'll be a scene where you see the solarisation effect. Adding the compression used in MPEG broadcasts is going to make this worse. People ask if they should enable Deep Colour on their BD players. The answer is, No. It changes the picture and not for the best. If the data isn't in the source then Deep Colour won't help. |
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#5 |
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Forum Member
Join Date: Apr 2006
Location: North Derbyshire
Posts: 41,794
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Quote:
I think they use pulse width modulation with the pulse width determining the amount of time the plasma cell is emitting. So to get the 30,260 levels presumably they have increased the pulse width modulator control from 8 bit (early plasmas with 256 or less levels) to 15 bit.
As I said above, to control the brightness you fire the cell those multiple times - so none at all for complete black, and 255 times for full brightness (assuming 8 bit control). |
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#6 |
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Forum Member
Join Date: Jul 2005
Posts: 7,052
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Yup, refresh rates and fancy talk about cells on and off asside, poor material and bit depth has more to play.
Bluray is best for less posteization It shows up more on these new higher contrast panasonics. Why this is I don't know- unless they are showing whats really there more so. |
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