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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  • kchase731 - Thursday, March 1, 2012 - link

    I have 2 of these side by side on my desktop. I bought them for $299 ea. free shipping. im very very pleased with them. I replaced 2 aging dell 2405's and these look really good. Im not a graphic designer or developer or gamer, i use them for work I like having the desktop real estate and these accomplish that well, maybe not perfect but like i said im not a designer and they seem very good for the money. i used a colorimeter to calibrate them, they seem accurate and crisp, im very happy with the purchase, and am strongly considering adding a 3rd.
  • mike8675309 - Thursday, March 1, 2012 - link

    Get this resolution into a 21" display and have it be at least as good as this and I'd buy a pallet of them to hold me over until retirement. At a 24" size, I'll just take two as it really is just too big to be perfect. As a software programmer (more actual code, less pretty widgets) those extra lines of resolution are valuable.

    Now if the company I'm working for today would just let me buy my own monitors.
  • Mithan - Thursday, March 1, 2012 - link

    I purchased this monitor back during the Black Friday sale they had in November and I love it.

    It sits next to my Dell 2407WFP which I love as well and replaces some crappy 24" Samsung TN panel that died on me.

    My only complaint with the LCD is that the vertical viewing angle isn't as good as the 2407WFP.

    However, for heavy gaming and web browsing, it has been an excellent LCD and I am tempted to buy a second to replace the 2407 that is taking longer to reach full brightness than it used too.

    Its a kick ass LCD, especially for $300. I would recommend it to any gamer in a heart beat that doesn't want a crappy TN panel but doesn't want to spend $500 either.
  • mtoma - Friday, March 2, 2012 - link

    I also thought that 120 Hz is good for movies, I even bought an LG and I watched movies in 120 Hz, for that reason only. Well, the movement scenes are .. uncanny, the feel like I watch some theatre piece, are toooo fluid. The action/movement scenes feel rushed. Too rushed. And, it makes sense: the movie, released to users in 23-24 frames/second, looks best on lower refresh rate panels.
    Of course, in other desktop applications (games, Internet, office apps), that refresh rate does not ruin the experience, it is ok. But in movies... no way, no way.

    On the subject of panel-integrated webcams, I agree that they suck. But, I believe that in smartphones (the expensive ones - Nokia Lumia 800 for example) they don't suck, actually are pretty good. So, I feel that desktop enthusiasts deserve the best technology possible. I really think that with a bit of effort, the PC world can match and even surpass the Apple world in technology and design (the design and the component consolidation are the reasons I wish a good integrates webcam in LCD-s/OLED's).
  • sethsez - Thursday, March 8, 2012 - link

    You're wrong about movies. Unless there's some interpolating going on (which might very well be the case), 120 Hz should be significantly BETTER for 24 FPS material than 60 Hz.

    The thing is, 24 doesn't divide evenly into 60. So you wind up getting unevenly repeated frames in order to match the monitor's refresh rate. Meanwhile, with 120 Hz you can repeat each frame 5 times and be done with it, ensuring an equal level of time between each unique frame.

    What you saw was almost certainly interpolation, in which the monitor actually attempts to create new frames in between the original ones. It looks like garbage and has given 120 Hz a bad rap it doesn't deserve.
  • woodelf - Friday, March 2, 2012 - link

    Here's my problem with this review and others (of both this monitor and others): I have no basis of comparison. Other than the Apple monitors, I have never even seen an 8-bit IPS monitor in person. And the last time I got to play around with an Apple display enough to determine how the color was (not as good as my CRT) was 2-3 generations ago. Best Buy doesn't stock anything but crap for monitors, and ditto for every other store I've managed to get into. Likewise, work monitors are (1) all cheap Dells and (2) running XP and ugly custom-built software, and I'm not doing any design work on them in any case, so I don't have anything to really judge against.

    Unfortunately, all I know from reviews is that S-IPS > eIPS > TN, and TN isn't good enough for my eyes. What I *do* know is CRT monitors (I'm a little behind the times). So, can anybody compare the color fidelity of an eIPS to a quality CRT (ideally my slowly-dying Sony GDM-FW900)? I get that S-IPS or H-IPS would definitely be preferable, and I suspect I could see the difference, at least in some circumstances. But this monitor is much more comfortable for my budget, so if it's "good enough", the sacrifice in quality is probably worth it to me. From looking at screenshots in reviews, I really can't tell the difference between a well-calibrated U2412M and U2410--but I don't expect that is representative of actually sitting in front of the monitors.
  • GullLars - Saturday, March 3, 2012 - link

    I've been using this as one of 3 monitors for 8 months now, and i'm very happy with it.
    My main monitor is a Dell Ultrasharp 27" (2560x1440), and i have this U2412M and another monitor in portrait mode (flipped) on either side. Upgrading from two old TN monitors, 1x 24" 1900x1200 and 1x 22" 1680x1050, using the new configuration is great.
    Using these U2412M vertically for reading documents and web sites are great. It gives a much more "roomy" feeling.
  • jiffylube1024 - Sunday, March 4, 2012 - link

    I've got the Dell Ultrasharp 709W -- it's a 16:10 27" LCD with a 1920x1200 panel. If they did a 27" 1920x1200 eIPS for a cheap price (<$500) I'd get it in a heartbeat, and I'd bet it would be a huge seller.
  • kunstderfugue - Tuesday, March 6, 2012 - link

    Something i don't understand is: How is 16:10 better than 16:9? In the end, it's only 120 more lines; and i don't see how that makes for a better experience.
  • woodelf - Thursday, March 15, 2012 - link

    It's not just 120 lines, it's also an inch (or so, depending on the overall monitor size). In the case of a 24" monitor, that extra inch makes it possible to see an A4 or letter-size two-page book spread at actual size, and still see your menu bars. In fact, the 16:10 aspect ratio is almost perfect, with a little room on one side for some pallets or tool bars.

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