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If I had two identical monitors and a video card with one DVI and one VGA port capable of dual-monitor output, and I connected one monitor to each port, would the displays look the same? (They will normally show different images in extended desktop mode, but will the colors be the same?)

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up vote 3 down vote accepted

You won't get the same colors. Two reasons:

  1. No two monitors are exactly alike, even if they are same model, from the same batch, etc. Moreover, as monitor "ages", colors will differ more than when they were new.

  2. VGA port involves double digital-analog convertion, first in the video card, then the reverse conversion in the LCD monitor. This conversion is lossy, and colors will differ slightly even if you connect DVI and VGA to the same monitor simultaneously and switch between inputs.

If correct color representation is important to you, get color calibration hardware and calibrate both monitors (and repeat that procedure every several months). Otherwise, colors/brightness will be different. Maybe not much, if you're lucky, but still perceptibly different.

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How much of the difference will be due to the first reason and how much will be due to the second? – Andrew MacFie Dec 26 '11 at 19:41
@AndrewMacFie: Depends on your equipment and its quality, hard to say... It is also very subjective. Reason #2 usually introduces either a very small difference, or very large (rare). Reason #1: depends on monitor's quality. Can be anything, especially in consumer-grade equipment. – haimg Dec 26 '11 at 19:53

I would say that it would really depend on the video card. I'm sporting a Radeon HD 6970 and have HP Monitors purchased at the same time plugged in. One is via DisplayPort to DVI, another DVI, and one VGA. The colors are all the same and looks good. I have a fourth monitor plugged in via the Onboard Graphics HD3000 and it is noticeably darker.

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The colors you will see depend fully on the monitor.

If you have 2 calibrated monitors (or 2 identical monitors) the colors will be the same.

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