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Display Calibration 201: The Science Behind Tuning Your Monitor

Application: How To Adjust Color Temperature

Assuming you’ve selected the User or Custom color temp preset, we can now adjust the RGB controls. You will need the meter again for this one. In fact, you’ve likely already gathered the data you need during the gamma adjustment step. If you’re using CalMAN, you might have a graph like ours.

There are two data sets here, the RGB levels for each brightness step and the Delta E error. Delta E is a value that expresses the amount of error for a particular color; in this case, white. We believe three is the point where these errors are visible, so we aim to calibrate our review monitors to a lower value. In the example, you can see that 0 and 10 percent have a little too much blue and the rest of the steps have too much green. We like this graph because you can see exactly what’s happening at every measurement point.

How do we fix this? Every monitor we’ve reviewed has only one set of RGB sliders, so we have to figure out what brightness level is most affected by those sliders. We always begin with an 80-percent window, and as it turns out, that is always the right brightness level for our adjustments.

Display an 80-percent window, place your meter on it, and set your software for continuous readings. That way, you can adjust the sliders in real-time and observe their effect on the white point. Here are the indicators we like to use from CalMAN:

The upper portion is a bulls-eye that makes it very easy to see which way you need to manipulate the controls to get the dot into the square. Below that are RGB Levels, which are also very easy to use. The goal here is to get all three bars lined up at 100.

Now, there’s just one challenge to this.

You’ll notice that the RGB sliders start at their highest settings, meaning your only option is to lower them. We would prefer they start in the middle, but most computer monitors are set up this way. Not to worry, though. If you need raise Red, just lower Green and Blue in equal amounts instead. That’s what we did for this monitor, HP's E271i.

Once you’ve adjusted your 80-percent window to perfection, take another full measurement run. In most cases, you’ll find that all levels are greatly improved and will have errors of less than three Delta E. If this is not the case, you may need to adjust a different signal level. While this is rare, it does occasionally happen. Adjust the window pattern that gives you the best overall average Delta E.

Here’s a sample of the final results.

This tells us everything about grayscale and gamma in one screen. The max white and min black numbers are in the upper-left, along with average gamma, Delta E, and contrast ratio. The gamma chart is in the mid-left. The upper-right has the RGB levels, followed by Delta E for every brightness step. And at the bottom is all the raw data. If your results look like this, you have a really good monitor. This one is a Samsung S27B970D.

If you’ve made it this far, you’re pretty much done unless your monitor has a color management system, or you’d like to create an ICC profile. We’ll explain how that works on the next page.

Christian Eberle is a Contributing Editor for Tom's Hardware US. He's a veteran reviewer of A/V equipment, specializing in monitors.