Pixel mapping, help me understand please

Discussion in 'Microsoft Windows' started by thehawk, Sep 4, 2007.

  1. thehawk

    thehawk
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    Good evening.

    I've been reading about 1:1 pixel mapping when connecting an LCD and PC together but I'm more confused than I was before reading anything :(

    I have so many questions rumbling in my head, I'll start with this one:

    If I decide to connect a PC with a 32" LCD(native resolution of 1366 x 768) which doesn't support 1:1 pixel mapping, what problems would I face?
     
  2. wywywywy

    wywywywy
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    Hi,

    Most people are probably too lazy to explain with words.

    The easiest thing for you to understand, is to change the resolution on your LCD monitor! For example if you LCD monitor's native resolution is 1280x1024, then try to change the Windows resolution to 1024x768, and you will understand what 1:1 pixel mapping is.
     
  3. scrambler2

    scrambler2
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    In the process of displaying a picture, there are two things involved. The resolution of the source (ie: your PC graphic card output resolution), and the resolution of the display (your LCD, plasma,native resolution).


    Normally if the resolution of the source matches the resolution of the display, it is a simple matter of putting each pixel of the source into the corresponding pixel of the display, no interpolation necessary, what you output is what you get on the monitor. This is what we call 1:1 pixel mapping (one source pixel for one display pixel)

    If the resolution of the Source does not match the resolution of the display, then some interpolation will need to take place. For example, if the output of the source is 1024x768, but the display is 640x480, several pixels of the source will need to be interpolated to fit in one of the pixel of the display (in this case the graphic card would do the job). As another example, if the output of the source is 1024x768, but the display is 1280x1024, then one pixel of the source would have to be interpolated into several pixels of the display (this could either be done by the graphic card, or by the display itself).

    Of course, when you have to interpolate, you bring in the risk of quality loss (depending how good is the interpolation, if it is up or down...)

    The term 1:1 pixel mapping comes into play because even when the resolution of the source matches the resolution of the display, there are cases where they will not be matched one for one.
    What happens is that most Monitors (TV) do what we call an overscan of the signal they receive. What that means is if you send them (in your case) a picture that is let us say 1366 x 768, they will not use the whole picture, but a slightly smaller portion of it (let us say 1311 x 737) basically throwing the edges away. When trying to display that smaller section of 1311 x 737 onto the display which is 1366 x 768, the monitor will need to scale up the image, so that it fills the whole display. As a result, you are not using the full image (loosing edges), and the scaling will result into an interpolation (1311 pixel are interpolated into 1366) that will create a loss of quality.

    On some monitor, you have the possibility to prevent the cropping and interpolation of the signal which comes into the display, by activating the 1:1 pixel mapping. If this option is available, when activated, the output signal of the source will be used as is (in its entirety), and each pixel of the source will be mapped to one pixel of the display. No loss of edges, no degradation of quality.

    This is especially important for people feeding a PC output to their display, so they do not loose the edges of the desktop image (from the cropping), an preserve an optimal quality for text readability (interpolation is especially noticeable and damaging on small text). Do wywywywy experiment below to see what we mean :)

    Hope this helps
     
  4. thehawk

    thehawk
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    Thanks a lot scrambler2, very very kind my friend. 1368x768 (meaning losing just a couple of pixels) ain't that bad I believe.

    Also, from what I understood, it is important to go not only for an LCD supporting the mapping but also a high-end graphics card, capable of 1366 x 768 resolution, right?
     
  5. naturbo2000

    naturbo2000
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    Kind-of.

    The big issue here is that you won't find a graphics card which does 1366 x 768 (1366 is not a multiple of 8, so your options are 1360 or 1368, which you use depends on what your (planned) TV might do with it).

    Nice panels (e.g. my getting old Hyundai Q261), will let you have a border of 6 black pixels if you feed it a 1360*768 signal - even let you have 3 pixels down each side if you want. Not-nice panels will stretch 1360 to 1366, which is fine for TV, but icky for a windows desktop.

    The other thing to check is what inputs accept what resolution, at what refresh rate. My Q261 will do 1360*768 1:1 at 60Hz over VGA or DVI, but only accepts 50Hz over DVI (and then scales it to 1366*768 - Argghhh!). It at least means I can use a windows desktop over VGA and have TV set @50Hz over DVI.

    Most recent graphics cards will support 1360 x 768, or at least can via powerstrip (Radeon 9x00+, Nvidia 6x00+).
     
  6. 16to9

    16to9
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    Well it's probably not as bad as trying to scale 1024 to 1366, but even two pixels difference will affect things.

    You'd probably see vertical banding across the screen - not too bad but still a bit of a moire effect.
     
  7. thehawk

    thehawk
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    Good morning friends.

    Today I connected my PC to my father's 26" Panasonic LCD, which doesn't have 1:1 mapping and I am very disappointed with the results. The only resolution which looked OK was 1024x768. Results where:

    1024x768
    - Desktop was stretched, text wasn't THAT good
    - DIV-X movie trailers with a high resolution looked pretty good
    - Low-resolution DIV-X looked so and so, no blacks on edges

    1280x768
    - Desktop was awful
    - DIV-X movie trailers with a high resolution looked pretty good, but not much better than 1024x768
    - Low-resolution DIV-X looked awful, blacks on each edge

    Other Resolutions
    - Either not supported or awful

    Allow me to ask you some questions, if I may:

    1. Why 1360x768 didn't look good if the LCD's native resolution is 1366x768?

    2. From windows, the monitor's refresh rate was set to 60Hz. When I loaded WinAMP, which is using a skin very similar to a 1:1 test I found in the forum(http://pixelmapping.wikispaces.com/space/showimage/pattern_original.gif),I could see flickering when using it. I tried changing the Hz to 75 and I saw a minor improvement. Is this because the LCD is not 100Hz?

    3. The maximum resolution according to Windows was 2560x1600. I assume that's the VGA card's maximum resolution, right? It's a Radeon AGP X1550. Could it be the reason why I didn't enjoy a nice picture?

    4. When watching satellite TV using a DVB-S2 tuner card, is the resolution up to the codec? Will I be as disappointed as I was with some low-resolution movie trailers?

    Hope you guys can shed some more light on this as - again - I was bitterly disappointed with what I saw this morning. Hopefully it's just the TV set.

    Thank you.
     
  8. jaymz

    jaymz
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    You need to check what reoslutions the TV can accept over the connection used. This may be different for VGA and/or DVI/HDMI.

    The native resolution of the TV and the maximum supported resolution that it can accept via a PC maybe different.

    The maximum resolution the graphics card can generate may be different to what your computer monitor can accept and therefore display. The maximum resolution your TV can accept and therefore display is likely to much lower than that of a computer monitor.

    Generally TVs are limited to 60Hz or 50Hz (although still not very common) over VGA.

    Your computer "talks" to your display (either TV or computer monitor) and "asks" it what resolutions can it display. The response is based on the displays EDID data. The computer will only then allow you to pick one of the resolutions that is in the EDID data. Some graphics cards drivers allow you to create custom resolutions or force feed a value. Powerstrip will also allow you to do this.
     
  9. thehawk

    thehawk
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    Thank you for the reply jaymz.

    Yes, I know the graphics card has a maximum resolution and so does the monitor/LCD. For this morning's test, I can say that:

    What I found is that the Radeon's max resolution is indeed 2560 x 1600 as windows showed. I can't find anything on the LCD's maximum resolution over VGA though :(

    I'm curious: would have I seen any improvement if my card had DVI/HDMI support and connected the PC to the LCD via DVI/HDMI?
     
  10. jaymz

    jaymz
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    The LCD's maximum resolution over VGA would normally be in the manual under PC input.

    As for improvement comparing VGA to DVI/HDMI that is generally done to the individuals eyes. I have used both on my 46" Samsung M87 and the only the real diffenrece is that VGA appears a little "softer".
     
  11. thehawk

    thehawk
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    How silly, I didn't look at the manual :)

    It says 1366x768 @60Hz as maximum resolution, which I tried but looked awful :(

    However I see that settings can be applied to PC input which I may try later and let you know.

    Thanks!
     

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