[mythtv-users] OT: LED or Plasma (was Advice on choosing a TV)

Paul Gardiner lists at glidos.net
Sat May 29 07:47:23 UTC 2010

Andre wrote:
> On 28 May 2010, at 10:17, Paul Gardiner wrote:
>> Andre wrote:
>>> On 28 May 2010, at 00:00, Paul Gardiner wrote:
>>>> Andre wrote:
>>>>> Alternatively and much more simply are you using studio levels (vdpaustudio) out from MythTV? If not there is a scaling of the display output 16-235 scaled to 0-255, this introduces some small artefacts that a plasma display will accentuate.
>>>> Now I have MythTv driving the TV, I'm getting results much darker than
>>>> any other source - all the others being much the same. I.e., dark areas
>>>> are darker. First thought when I saw this was that it might be
>>>> the 16-235 to 0-255 scaling, so I put vdpaustudio in the filter box.
>>>> It made no visible difference. Any other ideas? It would be really nice
>>>> if all my sources were the same, so I can just calibrate once.
>>> You should be able to see the difference vdpaustudio makes, I think we established that you have a critical eye ;-)
>> Cross posts. Turns out silly Paul didn't realise that 0.23 was out.
> Yessss, come back when you've upgraded, can't believe you can be subscribed here and not know about it!!

Ok sorted. vdpaustudio did it. Now all sources look the same to me now.

>>> Have a look for the full/video setting in the TV, the counterpart to vdpau studio also superwhite, worth checking RGB/YCrCb settings as you have already seen the green & magenta look that feeding RGB into YCrCb gives. Also you can have different settings per input so I'd swap the inputs around and determine if MythTV is really darker or just connected to a differently setup input. Bizarrely the only mode I could find all the settings exposed in with that TV was Game mode, which gave me the best results driven from a computer when correctly adjusted.
>> Don't see anything like that in the settings, but hopefully when I
>> upgrade I wont need to.
>> I never got to the bottom of my green magenta problem. I see what you
>> mean about it being Y mapped to u and or v. It looks like the nvidia
>> driver can't do interlaced modes properly.
> I thought it could now, maybe that's another 0.23 related thing.
>> I did see something odd in
>> Xorg.log.
>> GetModeLine - scrn: 0 clock: 13500
>> GetModeLine - hdsp: 720 hbeg: 732 hend: 795 httl: 864
>>              vdsp: 576 vbeg: 580 vend: 586 vttl: 624 flags: 26
>> Shouldn't vttl be 625?  If I set up a mode by hand with 625 in
>> place of 624 then the TV OSD doesn't say "576i".
> I'd try a modeline generator or better use the generic ones on the mythtv wiki.
>>> Really you need to calibrate from inside MythTV as well as DVD/Bluray, I'd start with Bluray to get a feel for it then go to Myth with a rip of the setup DVD or BBC HD Testcard, there are some free patterns you can download from AVForums too.
>>> Would be really really nice if VDPAU could be configured to output YCrCb instead of RGB but I don't know if it's capable or even if HDMI can use that colour space in computer display mode.
>> I've always thought that. We convert YCrCb to RGB in the frontend, and
>> then the TV converts it back to do its colour processing. Worse when
>> using S-Video or Component: we convert to RGB and then back again in
>> the front end.
> It's going to end up as RGB or something directly related for the display anyway but the reason the TV industry uses colour difference is that a slight level mismatch on a YUV signal creates a slight colour shift but black, white & grey are still exactly black, white and grey, and it doesn't look objectionable, whereas a slight level mismatch in an RGB signal gives a colour cast to everything and looks really horrible. Add to that Nvidia have a long and messy history of very slightly screwing up colour space conversions, some broadcast people refuse to use their cards and a realtime TV graphics system I use a lot VizRT often needs tidy up rework when switching to or from an Nvidia card, yes even with the $9k specialist cards, ATI usually get it right but vdpau wasn't invented or implemented by ATI so here we are.

I didn't think it was quite that. I thought our sensitivity to average
values of Y, U and V were pretty much the same, but our eyes resolve
detail in Y far more than U and V, hence the U and V can be decimated
in MPEG and put on a lower frequency carrier in analogue. The thing
I was saying about color controls in TV I'm not sure about: it was
just that I'd realised at some point that although naively you might
imagine that a TV taking a RGB input could map it straight through to
the "guns", but you'd still want brightness, contrast and color
controls and probably the easiest way to implement them is going to
YCbCr and back.

> I see varying colour casts in shadows with vdpau, I get a similar effect when I run my PS3 in RGB mode, playing the same video, in YUV mode the cast is gone.

That's interesting. Have you played with the itu709/itu601 setting with
that video?


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