Color output on monitors don’t match after calibration – why does that happens?
- Monitors can differ physically
- Monitors are not used in the same way, even standing side by side
- Full color management for all monitors is required
- Software must support color management and be used correctly
- Visual color match is necessary
Two calibrated monitors should have the same color output, shouldn’t they?
When two or more monitors are calibrated with a sensor like SpyderX and the software reports a successful calibration and the monitors don’t match visually – is there something wrong with the calibration?
Matching two monitors requires us to keep in mind five important points that we describe within the next few pages. One important thing that we want to mention right in the beginning of this article: You need a flexible and accurate calibration tool that is made for technically matching and visually tuning the color output of computer monitors, such as SpyderX Elite.
Point 1: If you want to match monitors, consider that they mostly differ physically. Monitor calibration will optimize and correct color output on a display, but it is not able to improve the physical quality. If one of the devices is a wide gamut monitor (which covers AdobeRGB) while the other covers a standard gamut only (sRGB), then higher saturated color outside sRGB can’t be reproduced by that standard monitor. Colors within the sRGB color space are covered by both and can be matched closely by following this article.
Point 2: Room light conditions as well as any color surrounding your monitor will influence your color perception. For this reason, it is very important to keep all conditions equal. This includes even the color of the background behind the monitors and the desk’s color. Also, the angle of view often changes the color perception. Simple displays with TN panel technology are more affected than better IPS panels, for instance.
Point 3: The computer system needs to handle all connected and monitors that are being used with full color management capabilities. This includes white point correction as well as linearization of the color primaries via LUT (Look Up Table) of the video card. While the white point will be handled by the image editor or browser, the linearization will be flashed to the LUT of the video card. It is important that the video card needs a separate LUT for each connected monitor.
Point 4: Some software tools don’t support color management. Microsoft’s Internet Explorer is one example, as is the Preview tool in Windows. The latest Firefox, Photoshop (all versions), Lightroom or other image editors handle color spaces extremely well. Only an overlapping window (between two monitors) won’t work, even when using one of the properly working tools mentioned. Opened files need to stay on one display only. In this case, when a file is moved from one monitor to the other, the full color correction will be applied in the moment you drop it (releases the mouse button) onto the appropriate monitor.
Point 5: Visual matching will always be necessary if you want to match monitors. This has nothing to do with the calibrator, rather it’s about human color perception. This is affected by personal white point correction. Like a camera, the human eye can only compensate one light source type at a time. But if there are two monitors side by side, they will differ in their color spectrum (even if both devices are LED screens). In the images on the right side, the white point was first set to daylight, second to the CCFL lights in the right showcase and third to the halogen lamps in the left showcase. The same effect occurs using two monitors – sometimes more, sometimes less. The human eye (here it was the camera) always compensates for the white point of the main light source, which is mostly the bigger and brighter monitor right in front of the user. In the same moment, the white point compensation doesn’t fit to the second monitor anymore. This can’t be corrected by a sensor, because this is an individual compensation, varying from person to person. The only way to match the second monitor to the primary one is to visually adjust the correct calibrated monitor in terms of its white point to the main monitor. Because this will be done in a linear way with the feature “SpyderTune”, the calibration will keep its accuracy, but match the white point as best as possible.
Here’s the whole process step by step:
This all starts in a dimly lit room set to approximately 100 LUX. (The reason why this is necessary and how to ensure the best possible room light level is described on the following page.) Now calibrate the monitors with SpyderX Elite and its StudioMatch feature. As long as the color space of the photo workflow is sRGB or AdobeRGB, the calibration target will be 6.500k color temperature and Gamma 2.2. The monitors should be calibrated to a luminance of 120 cd/m2. After these two calibration processes, the monitors are technically calibrated and matching. Due to the different light sources (see Point 5 above) users will see a difference in the white point. To compensate for that, use the feature “SpyderTune” to visually match the secondary monitor to the primary one. It is important that the main display stays as is and not adjusted after its calibration.
- Start in a very low room light (approx. 100 LUX)
- Calibrate monitors with SpyderX Elite and StudioMatch
- Calibrate primary monitor to the following target:
- 6.500k color temperature
- Gamma 2.2
- 120 cd/m2
- SpyderTune to match the secondary monitor visually to the primary monitor
1, 2, 3 – if number 1 is visible: clearly=monitor too bright – very barely=luminance is good – not visible=monitor too dark and/or room light too bright
Why room light conditions are so important
It’s really important to work in a dimly lit room – here’s why: Imagine that you are sitting in a pitch dark room, looking on your monitor showing a dark gray cross (RGB 4, 4, 4) on a black background (RGB 0, 0, 0) – you can barely see it. But what if you move your monitor in direct sunlight? Can you still see the cross? No, it’s not visible anymore, but what happened? The sunlight is so bright that your eye’s iris reduces the size of your pupil to a very small aperture. As a photographer you know that f22 is not the correct aperture to work in the darkness. So, your monitor shows you details, but you aren’t able to see it – that’s why post-production needs to be done in dim, ambient light.
Here’s an easy way to measure your room light: Take your camera and set it to the “S”-mode. Now set it to ISO 100 and your shutter speed to 1.0 second. (Be sure to set your exposure compensation to ‘0’.) Now cover your monitors with a cardboard or switch them off and focus your camera on your desk area. Then check which aperture value is automatically used by your camera. If this is between f4.0 and f5.6, your room light is a perfect level (around 100 LUX) to do image editing and post production.