Why don’t my monitors look the same after calibration?
Posted by Raphael Graf on 02 April 2015 09:42 AM

Visual observation of two monitors sitting side-by-side will never appear to match. Even if they are the same type, make and model, two displays will have subtle differences that are readily discerned in side-by-side comparison, but become negligible when each display is viewed separately.

Comparing a CRT monitor to an LCD monitor will be even less rewarding because of the inherent differences in display technology. In a side-by-side comparison between a CRT and an LCD, the LCD will always be perceived as 'brighter' and having 'higher contrast'. This is because the peak luminance of an LCD is typically about twice that of a CCFL, even when you calibrate both monitors to have the same Gamma and White Point.

To compound the effect, the organic eye-brain colorimeter (aka human color perception) causes one kind of difference to be perceived as if it were another kind of difference. Even if two samples have the same color but different luminance, they will be perceived as also different in color. Thus, when you calibrate a CRT and an LCD to the same Gamma and White Point and place the monitors next to each other, the fact that the LCD is twice as bright will cause them to appear different in color even if an instrument records identical chromaticities.

The human visual system has another powerful feature, referred to as 'adaptation'. For example, if you move from a room with incandescent lighting to one that is lit with fluorescent tubes, you will initially perceive white objects as having a bluish cast, and possibly brighter than they were. However, after a few minutes, your visual system 'adapts' to the new environment and your 'adapted' perception is that white objects are merely white.

Visual adaptation allows us to use two different technologies, like CRT and LCD, to view the same image file with similar perception. However, if you place two different monitors side-by-side and view them simultaneously, the visual system cannot adapt to both simultaneously. They will always appear different (in color, luminance and contrast) due to that very sensitive 'comparison' function of human visual perception.

Therefore, a side-by-side comparison of two monitors is not a reasonable metric for determining whether you can use each monitor individually and achieve similar results. A better test would be to put each monitor in a separate room, displaying the same image file (using the same software). Then view the image on monitor 1, allowing time for visual adaptation. Next, move to monitor 2, again allowing time for visual adaptation.

In such a test it is important to confirm that the image file being viewed has an embedded ICC profile that accurately defines its color space. Also that Photoshop's Color Settings are set such that the embedded color profile is used, and that each monitor is correctly calibrated, profiled and its profile is set as the current monitor profile.

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