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Discussion Starter · #1 ·
Simple question right? I'm just wondering why NO plasmas seem to have a native pixel resolution equivalent to any HD television standards? Most seem to be PC standards?


The DLP/LCP RPTV world however seem to make there sets at "normal" high definition vertical resolutions.


Can anyone explain this and more importantly what if any affect it really has on PQ?


Thanks,

Jon
 

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768 lines is actually essential a 3/4 scale of 1080. And before you start shouting, "Noooooooooo..... A 3/4 scale of 1080 lines is 810" understand that the 1080-line standard is 1024 lines of content with 56 lines of overscan -- technically. You know how the 1024-line ALiS plasma somehow magically avoid chopping off people's heads? Well, that's how.


The flipside is that 720 --> 768 scaling, while non-trivial, involves the creation of a fairly small number of intermediate pixels. If the display -- like a DLP -- had 720 lines, the 720p stuff would require zero scaling, but the 1080-line stuff would be a bit harder to deal with.


The truth is that none of this is perfect and yet none of it is bad enough to stop you and me, Jon, from enjoying either HDTV resolution.
 

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Rogo,


I am fiding many redundant paragraphs of text on the Net, but they all imply 1080 visible lines (that was my belief before your post).


The following link (see "What is interlaced scanning?")
http://www.twalbany.com/digitalenter...nt/hdtv.php#b7

states 1125 total lines not 1080.


Also, the first review I read in S&V (don't remember issue #) of a 1024 x 1024 plasma set (by Sony) clearly stated that lines are being chopped off from the top and bottom of the image.


Mike


-----------------------------------------------------

Always seeking the truth...
 

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Mike, maybe I'm wrong. In truth, I was fed this by Hitachi at CEDIA. I posted because (a) it might be true and (b) to see what kind of reaction it got.


Mark
 

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rogo> I posted because (a) it might be true and (b) to see what kind of reaction it got.


Truely a classic statement :)


But seriously, I think the visibility of the difference btwn. 720 lines and 768 lines to be very minimal at any reasonable distance. But some scalers will do this better than others. Consider the following two scaler approaches (though there are many others):


A1 - Every 15th line of 720 line (720p) source is replicated on the line below it on the 768 line display.


A2 - Every nth line on the display is the weighted average of the 720*n/768 rounded down and 720*n/768 rounded up lines of the 720 line source.


I'd think A1 much simpler to implement in H/W.

I'd think A2 is actually what *is* implemented in popular PC Display Adapters (e.g. ATI Radeon, etc...) and DigitalTVs today.

I'd think A2 might be trivially easier to implement in S/W but would require more CPU cycles.

I'd think A2 would produce the more evenly accurate picture.


Thoughts?
 

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It is my understanding that the ATSC spec calls for 1125 total lines, with 1080 lines containing picture information. The additional lines are for sync signals, closed caption information, etc.


If there is no overscan, then there would be 1080 lines. As far as I know, there is no exact standard for overscan and it varies from set to set. I suppose it is possible that plasma manufacturers may set the overscan to get 1024 lines shown on their displays.


Zenith's 60" plasmas all have had resolutions of 1280x720. Their upcoming model (Oct?) appears to have gone to 1366x768. I just thought I would throw this out there.


Robert
 

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emdc: I'm fairly sure it's A2.


Robert: My experience with a few plasmas is that with 1080i there is no apparent veritcal overscan. But that doesn't tell us much of anything, I confess.
 

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Discussion Starter · #9 ·
So what I'm hearing is that pixel/vert lines of resolution don't "really" matter so long as your close... so there nothing gained by being eaxactly 1080 lines vert... or 720 lines vert... vs. 1024 or 1280 700 or 740....


I was think, probably wrong, that the scaler was taking the whole picture and scaling it at once... no things make more sense.


Thanks,

Jon
 

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Jon, you can even be far off, so long as the math is easy.


For example, if you have a 1080-line feed, it's very easy to make a 540-line picture.


But even strange things like 1080 lines to 480 lines are not that tricky. I believe the 1080 lines are "bobbed" to 540 lines and then downsampled to the best 480.


The chips that do they are purpose built so they are fast and generally pretty good.


Mark
 
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