Picture This: LCD Market Watch
Nov 1, 2008 12:00 PM, By Jeff Sauer
A display shootout reveals there’s work to be done.
Dynamic LED backlighting yields very dark black levels and very high contrast ratios. This isn't surprising since the LEDs can be physically turned off. However, because the LEDs are clustered and they light regions of the screen rather than individual pixels, the testing report notes that “objectionable halos appear around bright objects that are embedded in dim or dark surroundings.” In other words, there's an inherent trade-off. Personal preference will determine whether the added contrast and black levels outweigh the halo artifacts.
Yet, clearly the most startling test results were in viewing-angle performance. It's a problem that's inherent to the way LCD produces images; that is, by shining light through a pixel grid (as compared to emissive technologies such as CRT and plasma). LCD TVs now regularly boast viewing angles between 170 degrees and 176 degrees. However, that can be misleading, as the shootout showed very overtly.
The image of the barn door on p. 24 shows the same image on the same screen from two different angles. When viewed straight on, the red color is excellent. However, at roughly 45 degrees, the display presents a severe color shift that can be seen in the image on the right. More surprisingly, when viewed in person, that color shift begins to appear outside a much narrower viewing angle; it's literally one step off-axis in either direction from the center. In the image of the young girl on p. 22, a slight move away from center turns a smiling, healthy-looking child into a more ashen-faced, unwell-looking girl as seen in the third LCD from the left. Neither the reference CRT nor the plasma showed any such color shift at wide viewing angles.
Why is this color shift not more visible to the average consumer? First, color shifts are far less noticeable on moving images than still images when one can move and witness a color change firsthand. Second, the specific images chosen by DisplayMate speak directly to thousands of years of human evolution: finding nutritious food to eat and recognizing healthy faces. How red a barn door is will likely pass right by the average viewer without the benefit of side-by-side comparison. And lastly, our eyes are generally not terribly astute about color.
Contrast ratio also suffered greatly in off-axis viewing. Test measurements taken at an angle of 45 degrees were, on average, about one-quarter of the contrast ratios measured straight on. The best 45-degree contrast-ratio performance came from Sony, dropping to roughly one-third the contrast ratio (467:1 at 45 degrees compared to 1344:1 straight on). Interestingly, while the panels with in-plane switching did a better job of maintaining color accuracy at wider angles, they suffered more loss of contrast both straight-on and from wide angles; this suggested another serious trade-off and a reason why the top-tier panels do not include this technology.
There is a lot to like about today's LCD panels and HDTVs. Image quality can be excellent, motion smooth, and colors strong, but DisplayMate and Insight Media have shown that there's still room for improvement as LCD looks to become the standard by which others are judged. The full testing report is available at www.insightmedia.info.
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