[mythtv-users] 720p plasma with myth

Rod Smith mythtv at rodsbooks.com
Sat May 1 00:20:45 UTC 2010

On 04/30/10 15:43, Mike Perkins wrote:
> Rod Smith wrote:
>> I've got a 1360x768 LCD set. (The manual claims it's 1366x768, but when
>> I used a custom Modeline to get that resolution I found that it was
>> cropping the left or right side of the image by a few pixels, whereas
>> it's fine at 1360x768. Thus, I believe the specs in the manual are just
>> plain wrong.)
> Surprisingly, it's not wrong. 1366x768 is chosen because it's just under
> a megapixel and (so I'm told) is suitably cheap for TV manufacturers to
> use.
> The reason why you're losing pixels either side: modelines must be set
> up as multiples of 8 pixels, hence 1360. I forget the reason, it's
> probably to do with shuffling things in and out of registers on the
> video card.

It was my understanding that this is true of nVidia drivers (or at least
some versions thereof), but not others. My system uses the built-in
Intel video chipset on my motherboard. Certainly X *CLAIMED* to be
running in 1366x768 mode (in its log files) when I set it up that way,
although I can't be sure that X was telling the truth. I know that
mythfrontend rescaled its display whenever I changed between 1366x768
and 1360x768, so I suspect that X was telling the truth.

That said, perhaps something similar to what you're saying was happening
in the TV -- that is, perhaps the LCD panel itself really is 1366x768,
but the circuitry doesn't accept that resolution on its VGA input.
(IIRC, the HDMI input was locked at 1360x768.) If this is the case,
though, it's effectively the same thing as having a 1366x768 display, at
least from a Linux configuration perspective. This possibility really
wouldn't surprise me, since it's a cheap off-brand TV (a ProScan).

> 3 pixels either side is neither here nor there. If you're that
> worried, why not select overscan? That way you'll get your 6 pixels
> back (but you'll lose them off the top and bottom instead :).

I'm not even remotely "worried" about it. It was just a parenthetical
comment in a longer post, intended mainly to alert readers to the fact
that tracking down a 1366x768 Modeline might not be worth the effort.

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