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Smaller than pixel?

Discussion in 'Graphics Cards' started by Aleksander, Apr 7, 2012.

  1. Aleksander

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    Hi all!
    I was reading an article of how gpus work and came upon a stunning and strange sentence:
    Pixels are not the smallest unit that can be addressed by the GPU :twitch:
    After reading it all, it didn't explain this.
    It would interest me a lot if it is not the smallest unit.
    Is it true? And what it is?
     
  2. Law-II

    Law-II

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    Hi

    It might refer to this - subpixel
    A component of a pixel. Three subpixels make up one pixel, namely one red, one green and one blue subpixel

    atb (all the best)

    Law-II
     
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  3. Jstn7477

    Jstn7477

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    Yes, pixels are made up of 3 primary colored "subpixels" that are controlled individually. The combination of Red, Green and Blue subpixels with differing brightness of each creates the color of each pixel you see. When all 3 subpixels are of equal brightness, they form the color White.
     
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  4. FordGT90Concept

    FordGT90Concept "I go fast!1!11!1!"

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    The smallest unit sent to a dispay is the pixel (with color information). Inside the GPU, it's all math. The GPU basically takes a snapshot of an area of the math, calls it a pixel, and sends it to output.
     
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  5. Jstn7477

    Jstn7477

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    Yes. The display then takes the "pixel (with color information)" and processes it internally, then sends the appropriate electrical signals to each subpixel and makes each subpixel twist a certain amount (for LCD displays, basically the liquid crystals in the subpixels twist to "open and close" the subpixel, essentially blocking the backlight and the subpixel color filter from being visible on the viewing side) or manipulates the electron beam in a CRT to hit the right phosphor pads that make up the subpixels with the correct level of energy.
     
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  6. theoneandonlymrk

    theoneandonlymrk

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    pixels dont exist to the geometry engine in a gpu or most of its core at all ,and untill the rops get involved they dont even matter or get considered
     
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  7. Aleksander

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    Ok now after the last comment i got confused!
     
  8. digibucc

    digibucc

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    yeah that's both a bit more info than necessary, and worded a bit confusingly. no offense to the last 2, but the first 3 replies give you a good short explanation.
     
  9. Kreij

    Kreij Senior Monkey Moderator Staff Member

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    Here's a bit easier way to visualize it.

    Let's say you tell your geometry engine (game engine) to draw a cube.
    At this point the engine has no concept of pixels as it only knows that there is a cube (of undetermined final size because it only has vector information) that uses a texture.
    The engine then takes other information (like scaling, rotation, lighting, etc), and creates your "rendered" cube, removing non-viewable information (based on camara direction) if told to do so, and also performs AA, AF, etc.
    It then looks at the viewport information to see where the cube is in relation to the camera (distance from you) and again sizes it accordingly using the screen capabilities (resoultion, etc.) in pixels.

    The order may not be exact in my example, but you can see why pixels have no meaning until the final output is displayed.

    Let's say you are playing Skyrim. If you're not you should be. :D
    If you tell the game to make an NPC twice the size (2x scaling), the number of pixels it uses on the screen is completely dependant upon where you are in relation to the NPC. Closer? More pixels, farther less.

    Here is info on subpixel rendering
    Subpixel rendering is a technique to give the impression of higher resolution due to the way humans see color combinations and the like.
    On LCDs (not CRTs) each pixel is made up of 3 color subpixels. There are still only X number of pixels on your screen.
     
    Last edited: Apr 7, 2012
  10. 95Viper

    95Viper

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    Cleartype uses sub-pixel rendering.

    ClearType

    Some info at GRC.com that is interesting: Sub-Pixel Font Rendering Technology

    Subpixel rendering From Wikipedia < Kreij beat me to the posting.

    Sort of interesting the way the mind and eye work.:)
     
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  11. Kreij

    Kreij Senior Monkey Moderator Staff Member

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    Hmmm ... it appears that sub-pixel rendering does have some effect (although not as good) on CRTs (it creates a slight blur).
    I assumed (apparently wrongly) that because the three color beams focus on a pixel and blend to create the pixel's final color, that the concept of sub-pixels didn't really apply.
    Perhaps the GCs are capable of minute adjustment to beam location within a pixel?
    I'm gonna look into this more. Quite interesting (to me at least :D ).
     
  12. W1zzard

    W1zzard Administrator Staff Member

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    direct3d doesnt support cleartype subpixel rendering. i think the OP is talking about something else.

    either everything before rasterization, which is just floating point math. or maybe some sort of antialiasing?
     
  13. Kreij

    Kreij Senior Monkey Moderator Staff Member

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    This is from a MS blog on the WPF Direct2d API

    And later in the blog ...

    Looks like DX10.1 and up support subpixel rendering. Another MS page on rendering tiers says subpixel (cleartype) rendering has been around since DX9. (shrug)
     
    Last edited: Apr 7, 2012
  14. W1zzard

    W1zzard Administrator Staff Member

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    yes but thats only for text. basically what you see on your aero desktop

    i dont think any game uses it, also it breaks when the screen is rotated and cleartype doesnt know about that
     
  15. Kreij

    Kreij Senior Monkey Moderator Staff Member

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    Yes. Since the subpixels are oriented in a horizonal only pattern, rotating the screen tosses it out the window. Kind of dampens the enthusuasm about SPR, expecially for things like eBook readers. :laugh:

    Looks like SPR is done in the shaders (2.0 and up), so it should be feasable in 3D. I read something about MSAA using a combination of SPR and AA, but I don't remember where I saw that.

    You're still writing GPU-Z in MFC (thus GDI/GDI+) aren't you? I think you can do it somehow using GDI+ but it doesn't sound easy, nor is it of any value for your utility. But if you ever get the urge to make GPU-Z a full 3D app .... lol
     
    Last edited: Apr 7, 2012
  16. W1zzard

    W1zzard Administrator Staff Member

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    gpuz uses subpixel rendering, like almost every other windows application that has standard windows controls

    afaik cleartype is not done in shaders. msaa is a completely different technology and does not look suitable to me for ultra high quality font rendering

    directwrite AA modes: http://msdn.microsoft.com/en-us/library/dd368118(VS.85).aspx
     
    Last edited: Apr 7, 2012
  17. Kreij

    Kreij Senior Monkey Moderator Staff Member

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    Windows controls only use it for the fonts, no?

    More info ...
    and ...

    Fun stuff.

    Edit : I saw the rendering enumeration page, but have no idea what "bi-level text" means. :roll:

    Edit 2 : My bad, I was going from memory (not a good thing when you get to my age. lol)
    It's not MSAA, it's Nvidia's SRAA (which was their response to AMD's MLAA) that uses post-processing techniques for subpixel fiddling.
    http://research.nvidia.com/publication/subpixel-reconstruction-antialiasing
     
    Last edited: Apr 7, 2012
  18. 95Viper

    95Viper

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    Aleksander Dishnica, is this where you found the statement?

    Allegro 5.1 reference manual
    And, the statement is on this page? Primitives addon

    Info: Allegro 4 and Allegro 5 are cross-platform, open source, game programming libraries, primarily for C and C++ developers. Read more details on the introductory page. This is the official web site.
     

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