Apple 27-inch LED Cinema Display Reviewby Anand Lal Shimpi on September 28, 2010 12:15 AM EST
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 both 200 nits of brightness for normal use, and 100 nits for print brightness. 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.
Uncalibrated the display's color accuracy isn't very good. I found the 27-inch LED Cinema Display to be way too blue and green out of the box, calibrated the display did much better:
The 27-inch LED Cinema Display isn't going to be winning any awards for color reproduction but it's good enough when calibrated.
Curiously enough, dropping brightness down to 100 nits caused a noticeable reduction in color tracking. The average delta E went up to 2.2 while most of the 27's competitors remained about the same. The 27-inch behaves very differently depending on what brightness setting you have it on.
Apple managed to do relatively well with the WLED backlight but it's still no match for the color gamut you get from any of the CCFL backlit displays. Note that my old 30 hasn't aged well, it's only able to cover roughly 73% today.