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In LCD monitors, is DVI mandatory in order to get 1:1 pixel mapping? Or is it possible with any VGA input?

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1:1 pixel mapping is intrinsic to DVI when resolutions are matched, but it's definitely possible to get the same result with VGA by calibrating your display. Here's how I do it:

  1. Find or make a 1px black and white checkerboard, like this one, and display it on the monitor in question at full size. If the monitor isn't calibrated, it will display a strong moiré pattern or display as blurry grey.
  2. Check that you're feeding the display at its native resolution
  3. Spend some time adjusting the coarse size controls on your monitor, then adjust position to match the edges of the panel. This is critical, especially if your monitor's auto-adjust doesn't function well. Once the size is correct, the image should look good or slightly blurry.
  4. Use the fine tuning controls to sharpen the image.

In the end, each pixel in the image from the computer (and the checkerboard) should match up with a pixel on the display.

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This is difficult to answer. At least, I can say, that VGA cannot be sufficient, because VGA is an analogue signal which has never heard of pixels.

DVI may be sufficient, but then, the monitor must not use overscan. Oversacan "zooms" up the picture to display a borderless image (mostly on CRT). But many LCD panels still have this overscan mode for backwards compatibility.

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In theory it could be possible using VGA with very precise calibration, although in practice yes you need the digital signal of DVI or HDMI running at the native resolution of the display for 1:1 pixel mapping.

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DVI is not mandatory. What is mandatory is that the monitor should be capable of handling the resolution as produced by the video card. This monitor resolution is called native resolution, meaning that optimal display quality can be reached only when the signal input matches the native resolution.

DVI is a video interface standard designed to provide very high visual quality. So, depending upon the quality of your video card and your monitor, you may need DVI for viewing on the monitor high resolutions issued by the video card at 1:1 pixel mapping.

If your monitor is not capable of displaying the maximum resolution as produced by the video card, DVI or any other technology will not make native resolution display possible, and you'll need to lower the video-card resolution in order to get, as per your question, 1:1 pixel mapping.

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99% of LCD panels with VGA just calibrate to the timing signals in a VGA signal and deliver 1:1 pixel mapping out of the box. Most panels do it automatically, some have a "Auto adjust" button. The amplitude of the RGB brightness is analog, but the timing is pretty accurate, so a monitor can fairly easy see what pixel belongs where, and this does not differ much from a digital signal. I don't understand the critics in other answers about the VGA signal being analog. The only real problem of the analog amplitude in the VGA signal, is the colour accuracy and the gray-ramp gamma, not the pixel mapping.

Things to watch: make sure the VGA signal is in the right resolution AND frequency. Most LCD panels need 60Hz signals, and nothing else.

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