[mythtv-users] PQ on DLP monitor

Robert Denier denier at umr.edu
Sat Jan 22 09:59:01 EST 2005


Your going to lose a bit using myth.  That is pretty much gauranteed due 
to the compression involved.  First off the analog to digital converter 
in the 350 might be as good as the one in your set, or it might not.  
For that matter, i'm not sure the TV requires one to deal with the 
component signals.

You want to
1) Set the brightness and contrast on the capture card to accurately 
sample the range of signals in your s-video connection.  Sorry I don't 
know how to do that in myth yet, but its probably documented somewhere.  
The only accurate way I know how to do it is to use virtualdub and look 
at the histogram and adjust it so that with a picture that contains lots 
of solid white and black and a nice gradient you completely use the 
sampling range available.  (A very tiny amount of clipping is ok.)  Of 
course you can always do trial and error.  I have no idea how good the 
defaults are on that card so I'm  not sure if this step will actually help.

2) Set the capture resolution as high as it will go as well as the data 
rate for the compression.  This will reduce further loss caused by the 
compression.

Then compare the two signals and try to tweak things to get as close as 
possible.  Will it be as good as the component connection?  I really 
doubt it, but perhaps  you can get it close enough that you can't tell 
the difference without really staring.

The ideal solution would be a satellite receiver that sends out the 
compressed mpeg2 stream so you don't have to capture it again.  Of 
course given intellectual property concerns and their dislike of making 
it easy to get perfect digital copies, I rather doubt its gonna happen.

Random thought:  If it were possible to synchronize three low cost 
capture cards and have each one capture black and white at say 640x480x8 
bit could that be used to capture 480i interlaced component video?  I 
suspect it would require a really high end system, and even then I have 
no idea if it could be made to work.  The amount of improvement would 
likely be tiny as well.





Footer wrote:

>I've been tweaking with xorg.conf for about a week now trying to
>improve the picture quality on my DLP monitor ... But maybe I'm
>"barking up the wrong tree" ... ?
>
>The hardware involved:
>
>   Samsung HLN 467W - 46" DLP digital monitor
>   Samsung SIR-TS360 - DirecTV HD satellite receiver
>   eMachines T3096 Media Center PC running Myth on FC2
>   Albatron GeForce FX5200P w/128MB DDR using DVI out to DLP monitor
>   Hauppauge PVR-250 capture using Svideo from HD satellite receiver
>
>The main question I have is how can I tell if I've reached the limit
>of the capture card vs. the video card?  Regular satellite or local
>channel broadcasts viewed directly from the receiver (hooked up with
>component video) look slightly better than through the Myth setup
>which is the FX5200P hooked up via DVI (live TV coming from the
>PVR-250 capture).
>
>Viewing Myth at 16:9 pretty much fills the screen except for a very
>narrow black bar on the right ... The FC2 desktop fills the screen
>completely and is actually slightly outside the frame all the way
>around ... and looks pretty good at 10' for a  46" screen.  Maybe I
>should take up gaming.  ;-)
>
>My current xorg.conf:
>
>==========
>
># Xorg configuration created by system-config-display
>
>Section "ServerLayout"
>    Identifier     "single head configuration"
>    Screen      0  "Screen0" 0 0
>    InputDevice    "Mouse0" "CorePointer"
>    InputDevice    "Keyboard0" "CoreKeyboard"
>EndSection
>
>Section "Files"
>
># RgbPath is the location of the RGB database.  Note, this is the name of the 
># file minus the extension (like ".txt" or ".db").  There is normally
># no need to change the default.
># Multiple FontPath entries are allowed (they are concatenated together)
># By default, Red Hat 6.0 and later now use a font server independent of
># the X server to render fonts.
>    RgbPath      "/usr/X11R6/lib/X11/rgb"
>    ModulePath   "/usr/X11R6/lib/modules/extensions/nvidia"
>    ModulePath   "/usr/X11R6/lib/modules/extensions"
>    ModulePath   "/usr/X11R6/lib/modules"
>    FontPath     "unix/:7100"
>EndSection
>
>Section "Module"
>    Load  "dbe"
>    Load  "extmod"
>    Load  "fbdevhw"
>    Load  "glx"
>    Load  "record"
>    Load  "freetype"
>    Load  "type1"
>    Load  "v4l"
>EndSection
>
>Section "InputDevice"
>
># Specify which keyboard LEDs can be user-controlled (eg, with xset(1))
># Option "Xleds" "1 2 3"
># To disable the XKEYBOARD extension, uncomment XkbDisable.
># Option "XkbDisable"
># To customise the XKB settings to suit your keyboard, modify the
># lines below (which are the defaults).  For example, for a non-U.S.
># keyboard, you will probably want to use:
># Option "XkbModel" "pc102"
># If you have a US Microsoft Natural keyboard, you can use:
># Option "XkbModel" "microsoft"
>#
># Then to change the language, change the Layout setting.
># For example, a german layout can be obtained with:
># Option "XkbLayout" "de"
># or:
># Option "XkbLayout" "de"
># Option "XkbVariant" "nodeadkeys"
>#
># If you'd like to switch the positions of your capslock and
># control keys, use:
># Option "XkbOptions" "ctrl:swapcaps"
># Or if you just want both to be control, use:
># Option "XkbOptions" "ctrl:nocaps"
>#
>Identifier  "Keyboard0"
>    Driver      "kbd"
>    Option    "XkbModel" "pc105"
>    Option    "XkbLayout" "us"
>EndSection
>
>Section "InputDevice"
>    Identifier  "Mouse0"
>    Driver      "mouse"
>    Option    "Protocol" "IMPS/2"
>    Option    "Device" "/dev/input/mice"
>    Option    "ZAxisMapping" "4 5"
>    Option    "Emulate3Buttons" "no"
>EndSection
>
>Section "Monitor"
>      Identifier   "Monitor0"
>      VendorName   "Monitor Vendor"
>      ModelName    "SAMSUNG DLP"
>      DisplaySize  1100       620
>      HorizSync    30.0 - 61.0
>      VertRefresh  56.0 - 85.0
>      Option      "dpms"
>EndSection
>
>Section "Device"
>    Identifier  "Videocard0"
>    Driver      "nvidia"
>    VendorName  "Videocard vendor"
>    BoardName   "NVIDIA GeForce FX (generic)"
>EndSection
>
>Section "Screen"
>    Identifier "Screen0"
>    Device     "Videocard0"
>    Monitor    "Monitor0"
>    DefaultDepth     24
>    SubSection "Display"
>         Viewport   0 0
>         Depth     16
>         Modes    "800x600" "640x480"
>    EndSubSection
>    SubSection "Display"
>         Viewport   0 0
>         Depth     24
>         Modes    "1152x864" "1024x768" "800x600" "640x480"
>    EndSubSection
>EndSection
>
>Section "DRI"
>    Group        0
>    Mode         0666
>EndSection
>
>==========
>
>Any and all comments would be GREATLY appreciated!!!
>
>Thanks,
>TLD
>  
>
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>
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