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We are using a Spectracal-certified X-Rite i1Pro, along with CalMan, to report color gamut and color accuracy. For those unfamiliar with the terms, color gamut refers to the range of colors that a display can reproduce, and color accuracy refers to the display's ability to output the color requested by the GPU. Typically, professionals represent these values by showing a gamut and a delta E value, which is a mathematical representation of how far apart the display's output is to the original source. The higher the delta E value, the more inaccurate the color representation. An uncalibrated delta E is largely a worthless number. Delta E is dependent on the black and white luminance levels, contrast ratio, color temperature, and target gamma.
Suppose there are two displays. One has an uncalibrated delta E value of 3.0, and the other, 2.1. It is hard to make a comparison without first calibrating the color space. It's almost like benchmarking a GeForce GTX 580 at 2560x1600 with anti-aliasing enabled against a Radeon HD 6970 at 1920x1080 without AA. Do the results of that test mean the 580 performs better? Not necessarily. Monitor calibration is to display quality what quality settings are to game benchmarks. By calibrating a display, we are able to normalize the settings and see how one display compares to another.
For this reason, we provide information in the form of a color gamut map, along with a gamut luminance chart. This gives you a better picture of how a display performs, both fresh out of the box and once it's calibrated.
Color Gamut and Accuracy
CalMan uses specific targets, which are displayed as squares in the gamut xy map. The dots are the actual measured values. Gamut luminance expresses how bright the primary and secondary colors are in relation to the source color requested by the GPU (gray bars are target values).
Gamut CIE XY Map
Expectedly, Dell's UltraSharp U2412M again leads the pack in color production thanks to its e-IPS panel (though the default gamut benchmark already shows how its lower-cost e-IPS panel compares to premium offerings that employ higher bit color depth). The U2412M is only capable of producing a little over 70% of the AdobeRGB 1998 color gamut in perceptual rendering (read our printer paper benchmarks if you want an explanation of perceptual rendering). Compare this to the 27" H-IPS and p-IPS (p for performance) monitors from our last round-up able to generate nearly 100% of the AdobeRGB 1998 color gamut.
As we turn to color quality, we again see a scenario where IPS and TN technologies differ. Many TN-based monitors have a strong tendency toward blue and yellow production because they use a blue LED with a yellow phosphor to achieve white. Most manufacturers compensate by steering calibration towards green, and that's a problem we see evident in the mapping of green in the CIE XY map for the S242HL bid and T24A550. Due to the wider gamut of IPS panels, it's more difficult to address this issue without adversely affecting the whole color palette, which is why blue luminosity seems a little high on the U2412M right out of the box.