[mythtv-users] HDTV on Myth -- is it a "myth?"

Cory Papenfuss papenfuss at juneau.me.vt.edu
Mon Oct 11 14:31:33 UTC 2004


>>     Same frequencies for the TV, agreed.  It's not exactly the same, 
>> perceptually, however.  An 1080i signal will resolve higher vertical 
>> resolution (Kell factor notwithstanding) than a 540p signal, even though 
>> the TV's H/V PLL's will by running at the same rate.  The difference would 
>> be most apparent on a still frame with horizontal lines on it.... annoying 
>> 30Hz flicker, granted, but higher resolution yes.
>
> What I'm saying is that for 1080i, the TV electrically has *no way* of 
> telling the difference.  The signals transmitted are identical, whether the 
> hardware sends each field, or if you run bob deinterlace in software and send 
> the exact same fields sequentially.
>
> Note that this is untrue for NTSC and its 525 lines, where one frame has one 
> more line than the other.
>
> -Doug
>
 	That's what I thought I said.  Frequencies are the same.  What 
about the 1-line offset though?  I believe that even with the same number 
of lines/field, the monitor still has to know that it's interlaced so it 
can interleave the lines spatially.  Otherwise, the two frames will draw 
sequentially on top of each other.  I think that an interlaced signal 
often swaps between positive and negative VSYNC polarity on the redraw to 
indicate interlaced.

 	That would be the ideal situation, but I know that some monitors 
don't know the difference and draw one on top of the other (like you 
suggest).  Either way, it's not going to hurt the monitor since the 
freqencies are the same.

-Cory


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