Delta E Testing and Why Our Numbers are Different

If you’ve looked at reviews of the Dell U2412M at other sites, you’re going to find that our Delta E (dE) numbers look different, as do our other display reviews. This leads to several questions: why are our numbers different, what do they measure differently, and what results should you believe? In reality you should believe all of them, as they are all accurate, but likely reporting on different things. To explain this more, let’s look at how profiling a display works.

We use ColorEyes Display Pro for our device profiling and measurements, and I use an i1Pro for all of my profiling and profile evaluations. In creating a profile, ColorEyes Pro uses a fixed set of patterns that it moves through, adjusting the response curves for the display as well as creating Look Up Tables (LUTs) that contain information about how the display responds to colors. Using the curves we get a linear grayscale and accurate gamma out of the display. Using the LUTs we get the correct colors out of the display. If we ask for red, it looks at the LUTs to see how the display creates red, and then adjusts the signal going to the display to accurately reflect what the program is asking for.

This is exactly where we can get the difference in results but still have them be accurate. Sites use different software to evaluate displays; I haven’t used all of the packages available so I don’t know specifically how each works. However, if they were to use the same swatches in profile creation that they use in profile evaluation, then the results should always be near perfect. If the LUT contains the exact color you are trying to measure against, then it knows exactly how the display handles that color and it should come out close to perfect. If you try to look up a color that isn’t in the LUT, then you’re going to have to interpret how to create that color and will likely be off by a certain amount.

When calibrating a TV, people almost always use the first method. We calibrate to the RGB primaries (and CMY secondaries), measure how close they are, and assume the intermediate colors will be created correctly. One benefit is it is very easy to compare across different reviews as we all have the same targets. Sometimes we find after viewing test material that something is wrong and making those 6 points correct caused the millions of other possible points to be incorrect. This could be due to the lack of bit-depth in doing calculations and causing posterization, an incorrect formula, or something else. Some programs might do the same thing in that they create a profile for the display, but then they only check against colors that are in the LUT and so will be accurate.

We check color fidelity using the well-known Gretag Macbeth color checker chart. This is a collection of 24 color swatches that are common in daily life, like skin tones, sky blue, natural greens, and more. None of these are typically contained in the LUT of the profile, so we are finding out how well the display can do these other shades and not, in a way, cheating by using known values. Because of this we expect to encounter a higher amount of error than other tests might, but we also believe it is closer to real world results.

The other main source of error using this method is colors in the chart that are outside of the sRGB colorspace or at the very edge. Since GMB was designed around real world photography and not computers, some of these swatches are much harder to reproduce. This helps to separate displays with larger color gamuts from those with smaller gamuts in testing, rewarding them with lower dE values in the end. It also can reward displays that have their own, built-in LUTs for doing calculations and not those that just rely on the LUTs in the graphics card.

So when you look at an LCD review, remember that one dE isn’t the same as another dE. Both are valid but both are potentially measuring very different things. I could easily put up the dE values that ColorEyes Pro generates when it verifies a profile and every display would have a value well below 1, but that wouldn’t be as useful or informative as the current method.

Dell U2412M Design, OSD, and Viewing Angles Dell U2412M Color Quality
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  • klatscho - Tuesday, February 28, 2012 - link

    we sort of downgraded from eizo to these beauties, and the do the job quite nice, especially since we got them way below the 200 euro mark including the soundbar - which is why everyone is getting one now.

    the only problem we have identified so far is an unusually high doa-rate above 6% at the beginning, which has meanwhile dropped to around 4% for the last couple of hundred units; but again, at this price this is forgiveable.
  • Touche - Tuesday, February 28, 2012 - link

    Although it could be calculated (if contrast is consistent across the brightness range), it would be helpful if you showed the black level at calibrated brightness setting (100 cd/m2).
  • cheinonen - Tuesday, February 28, 2012 - link

    I can add that to future reviews.
  • anactoraaron - Tuesday, February 28, 2012 - link

    Please correct me if I'm wrong but this panel beats the U2312H from last year in power draw since last year's 2312 uses ccfl, not led like this panel.

    I personally didn't HAVE to have the 16:10 and recently bought 2 of the updated U2312HM which also uses led. But I always hear "once you go 16:10 you never go back" and I guess I'm just scared that will happen....

    Sure the styling isn't "sexy" but I'm a man that prefers function over all. At least comment on how there's ZERO glossy surfaces on these monitors...

    Also, the stand with these Dell monitors are top notch. They adjust more than ANY monitor I have ever encountered- 9" of height adjustment (for the newer U2312HM- I believe the U2412 has 7") , can spin to portrait orientation (just need to release a locking mechanism), and it can basically do more twists and turns than anyone's parents at a 1950's themed dance party. :)
  • 1ceTr0n - Tuesday, February 28, 2012 - link

    The U3011 is a beautiful monitor but for $1200, I demanded perfection and all three models had color uniformity and lighting issues.

    I finally gave up and got a U2412M and i've been very happy with it. Very nice bright and even LED lighting, very low heat, great colors and nary any ghosting and a great price with extended 4 year advance warranty.

    Unless your anal about LCD's, this one is hard to beat
  • fausto412 - Tuesday, February 28, 2012 - link

    Do 120hz IPS 24" 16x10 Monitors exist and are they any good and affordable?

    I've been waiting for that "I gotta have that monitor!!" review for like 2 years.
    Currently using 22" Samsung 226bw and the view angles suck balls. But considering how long monitors last I am trying to wait for the next huge leap forward to get a 24" screen and upgrade. what say the monitor experts on this thread?
  • cheinonen - Wednesday, February 29, 2012 - link

    There are no 120Hz IPS panels yet, you are stuck with TN at this point. I have no idea if there is a time frame for these or not either.
  • Oxford Guy - Thursday, March 1, 2012 - link

    120 Hz A-MVA panels are supposed to be near.
  • Oxford Guy - Sunday, March 4, 2012 - link

    They were announced in December: hz amva&ie=utf-8&oe=utf-8
  • fausto412 - Thursday, March 1, 2012 - link

    sadly i don't know what's holding back monitor makers.

    I feel like they quit trying to advance tech for home users.

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