Display Testing

With all of the extra connectivity there is to test with the Thunderbolt Display we can't forget the actual panel testing. Thankfully this part is pretty simple, the display characteristics are near identical to the 27-inch LED Cinema Display we reviewed last year.

Color Quality

We report two main quality metrics in our display reviews: color accuracy (Delta-E) and color gamut. Color gamut refers to the range of colors the display is able to represent with respect to some color space. In this case, our reference is the AdobeRGB 1998 color space, which is larger than the sRGB color space. So our percentages are reported with respect to this number, and larger is generally better.

Color accuracy (Delta E) refers to the display’s ability to display the correct color requested by the GPU and OS. The difference between the color represented by the display, and the color requested by the GPU is our Delta-E, and lower is better here. In practice, a Delta E under 1.0 is perfect - the chromatic sensitivity of the human eye is not great enough to distinguish a difference. Moving up, a Delta E of 2.0 or less is generally considered fit for use in a professional imaging environment - it isn’t perfect, but it’s hard to gauge the difference. Finally, Delta E of 4.0 and above is considered visible with the human eye. Of course, the big consideration here is frame of reference; unless you have another monitor or some print samples (color checker card) to compare your display with, you probably won’t notice. That is, until you print or view media on another monitor. Then the difference will no doubt be apparent.

As I mentioned in our earlier reviews, we’ve updated our display test bench. We’ve deprecated the Monaco Optix XR Pro colorimeter in favor of an Xrite i1D2 since there are no longer up-to-date drivers for modern platforms.

For these tests, we calibrate the display and try to obtain the best Delta-E we can get at 200 nits of brightness for normal use. We target 6500K and a gamma of 2.2, but sometimes the best performance lies at native temperature and another gamma, so we try to find what the absolute best performance could be. We also take an uncalibrated measurement to show performance out of the box using either the manufacturer supplied color profile, or a generic one with no LUT data. For all of these, dynamic contrast is disabled.

Color Tracking - XR Pro and Xrite i1D2

Uncalibrated performance remains fairly similar to last year's LED Cinema Display, however once calibrated the Thunderbolt Display is spot on with its predecessor:

Color Tracking - XR Pro and Xrite i1D2

As we mentioned earlier, a sub 2.0 delta E is good enough for professional use. Although not perfect the Thunderbolt Display falls within that range for sure.

LCD Color Quality

We measured slightly lower color gamut on the Thunderbolt Display than the original LED Cinema Display, however the result was much closer to the 2011 27-inch iMac. I couldn't visibly tell any differences and Apple indicates that color gamut shouldn't have changed, so it's quite possible that the differences here are due to our colorimeter and not the panel.

Color Uniformity

Now for color consistency, we take our best calibration profile from the very center at 200 nits and test color accuracy at 9 different places around the LCD display in an evenly distributed grid. We’ve shown before that calibration is localized across the display, partly due to the brightness not being uniform, partly due to the discrete nature of the display itself.

LCD Color Uniformity

The Thunderbolt Display was fairly uniform across its surface, something we noticed in reviewing the 27-inch LED Cinema Display last year. Uniformity is actually better on this panel than the one we reviewed last year, although in both cases I couldn't really tell any differences.

Peak brightness appears down slightly, but so are the black levels which result in a slightly better contrast ratio. Apple is also calibrating these things at the factory now so white points are now set at around 6300K vs. 7100K on the original 27-inch LED Cinema Display.

Thunderbolt Performance Display Testing - Brightness/Contrast & Uniformity
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  • Boopop - Friday, September 23, 2011 - link

    OK, so my Dell 2408WFP isn't as big, but in most if not all the tests it outperforms this new monitor. If I was a graphic designer (which I'm not!), even if I had a MBA I reckon I'd stick with a higher quality monitor, and put up with the extra cables.

    On the other hand, if I was the average Joe Bloggs with a MBA, this makes a great monitor for that specific laptop. I like where Apple are going with this, it's just a shame about the lack of many USB ports, and the average screen quality.
    Reply
  • IceDread - Friday, September 23, 2011 - link

    Normally when you test a display you also test the input lag which I find very important. I could not find info about input lag in this review. Reply
  • tipoo - Friday, September 23, 2011 - link

    Not really as important to the target demographic, I think. Most people who get these will be using them for professional tools, so things like colour accuracy are more important than reaction time. If someone is buying one of these and a mac to game on, they've made a pretty bad error, lol. Reply
  • jecs - Friday, September 23, 2011 - link

    You have the general idea right.

    For professionals not demanding the highest color accuracy for print or for broadcast production yes, the Apple monitor is a good choice. That is professionals who work on content creation like internet video, corporate videos or print material among others.

    Serious print houses, photographers or broadcast professionals will choose high end specialized monitors in the range of $3000+, not in the sub $1000.
    Reply
  • JasperJanssen - Saturday, September 24, 2011 - link

    But they will generally only choose that type of monitor for *one* display, where the guy sits who does final colour correction on the output -- not for all the content creation people. (fair enough, if you're large enough that's multiple people, but it's never going to be the majority of your staff). Reply
  • Anand Lal Shimpi - Friday, September 23, 2011 - link

    We normally test input lag by driving a CRT in parallel with the display being evaluated. I didn't have a good way of doing that with a Thunderbolt display unfortunately :-/

    Take care,
    Anand
    Reply
  • JasperJanssen - Saturday, September 24, 2011 - link

    Well, keep it on the list for when the Mac pro comes out, which will hopefully have a videocard with multiple thunderbolt outputs :)

    Come to think of it -- new iMac with dual thunderbolt out and one of them through a VGA dongle? Hmno. Those are active dongles, which mess up results.

    Two PCs, using NTP or something similar to sync up their internal clocks maximally, and one driving a VGA CRT with the other driving the thunderbolt display, each displaying very precisely the current system time in a large font, plus the usual fast shutter speed photography. Your accuracy would depend on the NTP-or-similar protocol. I wonder if you can get close enough with that, over a crossover Gigabit ethernet kept free of other traffic.

    If you do get something like that running, you can also compare input lag between:
    - Display port driving Displayport display
    - Thunderbolt port driving Displayport display
    - Thunderbolt port driving Thunderbolt display
    -Thunderbolt port driving thunderbolt display switched through another TB device or display (add to the chain as possible)

    And even whether displayport mac versus thunderbolt macs are different in this respect when running over the various dongles.

    I would expect a Thunderbolt port running in Displayport mode to be very slightly slower than a real displayport, would be interesting to see if that is the case, and how it compares to a TB port in TB mode, and whether other devices on the chain affect it.
    Reply
  • JasperJanssen - Saturday, September 24, 2011 - link

    "NTP v4 with kernel mods to support it, is capable of much better than 1ms accuracy, possibly as good as 1ns. According to his article, NTP v3 is accurate to 1-2ms in a LAN and 10s of ms in WAN nets. "

    Well, since what you need is ms range, I guess this could actually work.
    Reply
  • sheh - Tuesday, September 27, 2011 - link

    I was curious about that too. Regardless of who the target audience of the monitor is, it's a new technology so I'm curious about its performance vs. DP/DVI/VGA. But could be difficult to tell apart from the panel's logic own latency, at least until there are more TB displays. Reply
  • MrJim - Friday, September 23, 2011 - link

    The Youtube-video in this article, http://www.youtube.com/watch?v=LtAgkIE42jc&fea... , is private. Hard to see then :) Reply

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