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Display Quality: Color Gamut

Asus' Eee Slate EP121/B121: A Windows 7-Based Tablet PC

Interestingly, Asus is using a Advanced Fringe Field Switching (AFFS) panel on the Eee Slate (despite initial claims of an IPS screen). AFFS is supposed to be similar to IPS in that both technologies don't suffer from color loss at wide viewing angles. 

The EP121's AFFS screen does boast decent viewing angles like many IPS monitors we've tested, but that's where the similarities seem to end. When we look under the microscope, the subpixel structure of the AFFS panel looks similar to some of the competing TN panels. That's a precursor to the disappointing results you're about to see.

Asus Eee Slate: LCD Color Gamut (AFFS Panel)

Unlike tablets, tablet PCs do honor ICC color profiles, which makes benchmarking and calibration easier on the Eee Slate than some of our past tablet stories. However, most people won't bother going through the effort or spend the money for a professional calibration, which is why we're looking at default LCD performance.

Based on spectral analysis, we found that Asus's LCD panel is using a blue LED with a yellow phosphor to achieve white. That's pretty typical of LED-backlight panels. However, with TNs specifically, this results in a strong bias toward blue and yellow production at the expense of every other color. Oddly, while the EP121 uses an AFFS panel, it behaves like a TN panel when it comes to color production. Compared to the VA and IPS panels seen on other tablets, the Eee Slate is outpaced in every area but blues and yellows.

These gamut measurements are preceded by a couple of caveats. First, we disable dynamic brightness because it doesn’t allow us to get an accurate (or reproducible) measurement of the display’s potential. Second, brightness is set to the highest value. If you don't use the same settings, your color gamut is going to look smaller than what we're showing here.

The Eee Slate has a sub-par contrast ratio due to its relatively poor white luminance. Motorola specifically chose a VA panel for its Xoom due to that technology's ability to produce great blacks, while Apple opted for an IPS panel with high white luminance. AFFS is supposed to offer performance similar to IPS, but we're not seeing it on the EP121.

Color temperature is very close to a balanced 6500 K, but the low gamma distorts color perception. Gamma doesn't affect black or white performance, but it does affect midtones. If gamma is set too high, midtones appear too dark. If it's set too low, they're too pale

Adobe, Apple, and Microsoft all recommend a gamma of 2.2. It's an arbitrary value carried over from the NTSC standard, but it was originally chosen because it allows colors to appear more natural in slightly dim environments. The Eee Slate's relatively low gamma value suggests that it's best used in a nearly dark environment. Apple sets the gamma on the iPads much closer to 2.2, which is why colors appear less washed-out when you're outdoors and in well-lit spaces.

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