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Discussion Starter · #1 ·
Greetings,


It seems like one of the big headaches with HDTV is the two different HD-ish resolutions: 720p and 1080i. Some networks have chosen one format, and some have chosen the other.


Meanwhile, some display vendors have chosen to support only one or the other (am I right that Panasonic is one of the few to do 720p in a RPTV?).


To further complicate matters, some HD displays have a rigid pixel structure (DLP, D-ILA), so they must convert all inputs to match the resolution of the device.


One prime example of this oddness is the Mitsubishi DLP television. The DLP element is a native 720p element, at the precise resolution of 720x1280. And yet, the inputs it supports on its component ins are 480i, 480p and 1080i, but not 720p!! Maybe when the "promise" tuners come out, they'll take a 720p broadcast straight to the element at native resolution, but I don't know.


The other example is the D'Ahlia from JVC. Its element is not precisely sized to match any particular resolution of HDTV (it's 1028x1280, if memory serves). I would assume that it's a progressive element in at least some sense, because I can't imagine turning off alternate scan lines on alternate fields, but maybe I'm wrong. In any event, it also only accepts 1080i. So, no matter what, it's going to be scaling. It has a DVI input, but I haven't seen anything to tell me what sorts of resolution it accepts on that port.


So, this brings me to my question. I'd like to know just how good the current scalers are, and what kind of artifacting is experienced going from one resolution to another, and especially from progressive to interlaced and vice versa.


I imagine one particularly degenerate case. Let's say that ABC broadcasts a show in 720p. I receive it on a set-top, and to accommodate the input requirement for the D'Ahlia, the set-top converts 720p to 1080i. The 1080i goes to the D'Ahlia on the component ins, and the internal electronics re-scale it to match the display element. So, we've gone from progressive to interlaced and possibly back again (depending on the ILA element), and we've switched resolutions twice. I expect some artifacting. What I wonder is whether I can live with it.


Now, let's imagine the DVI input case. If the D'Ahlia could take a 720p signal on the DVI and scale it directly to its native element resolution, I would expect MUCH better results. But, again, I don't know what resolutions the DVI input supports (or what resolutions the announced satellite and cable STBs with DVI outputs will support). Even if it only takes 1080i on the DVI, at least there would be one fewer D/A->A/D step coming from the STB.


I'd be very interested to hear the thoughts of the experts here.


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

Mike Kobb

(Formerly "ReplayMike", but no longer affiliated with the company; these opinions are mine alone.)


[This message has been edited by JustMike (edited 08-07-2001).]
 

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Discussion Starter · #2 ·
(nudge)


Anybody? Actually, it seems as I think about it like you're even worse off with the 720p-native DLP's in the degenerate case I listed. You go from 720p to 1080i, then back to 720p. That just seems sad and unnecessary. Do any of the DLP's have a 720p input? The Mitsubishi doesn't, and I couldn't find info on the Panasonic.


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

Mike Kobb

(Formerly "ReplayMike", but no longer affiliated with the company; these opinions are mine alone.)
 
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