The New Wave of LCDs

Posted 09/05/2008 at 9:00am | by David Murphy

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Buying a new monitor can be tricky. First, you must decipher the manufacturer doublespeak. Not all specifications are created equal, nor are they measured fairly: You truly can’t tell a book by its cover, nor a monitor by its box copy. And then there are the displays themselves. A monitor by itself might look good to you, but you won’t know what you’re missing unless you compare it against the competition.

That’s why we’re here to help. The market is flooded with configurations, technologies, and sizes that might look good on paper or even attractive in the store, but that doesn’t mean these monitors represent the best of their class. You owe it to yourself to understand all the options. What does color gamut really mean? How do you know if a panel has 6-bit or 8-bit color depth? And how do those matters and others impact the overall image quality of a screen?

We’re going to walk you through the basics of today’s LCD monitor technology and what it means to you, a consumer who wants the best picture for your pennies. But we’re not going to leave you hanging: We’re also going to review 10 monitors across a wide swath of sizes and prices to give you a head start on your purchasing decision.

In the end, you’ll get the picture—the picture you deserve!

Understand the Technology

What’s important? What’s hype? What do those numbers on the box mean? We’re glad you asked

Color Gamut

The triangle in the center of this chromacity
diagram represents the NTSC color gamut,
used to measure the color output of LCDs.

The human eye can perceive a far more expansive range of colors than a computer or television display can produce. The subset of colors a display is capable of producing is defined as its color gamut. Typically, a display’s gamut is measured as a percentage of the National Television System Committee (NTSC) color standard, with 72 percent of that range being standard for LCDs. Recent technology advances, however, have enabled displays to reach 92 percent and even beyond 100 percent of the NTSC. But the expanded range of colors can come at the cost of color precision if a display’s color depth hasn’t increased as well.

Color Depth

An LCD’s color depth defines the number of levels that each primary color can render. In an 8-bit panel, the red, green, and blue channels of a pixel are capable of 256 levels each. Multiplied, that makes for a total of 16.7 million possible colors. (This number doesn’t change if the display’s color gamut broadens; the space between colors only widens, thereby diminishing color precision.) With 6-bit LCD panels, which are increasingly common, the red, green, and blue subpixels of a single pixel are capable of just 64 levels each for a total of 262,144 colors. That’s a big drop from their 8-bit counterparts. To compensate for the difference, manufacturers use techniques such as dithering and frame-rate control on 6-bit panels to expand their palettes. Traditionally, these techniques have been able to elicit up to 16.2 million colors, but it’s now common for 6-bit panels to claim 16.7 million colors, making it difficult for consumers to discern whether a display is actually an 8- or 6-bit panel. See the sidebar on this page for more on this issue.

Backlight

The vast majority of desktop LCD monitors have backlights made of cold-cathode fluorescent lamps (CCFL), but the use of LEDs for backlights is rising. LED backlights use a grid of either white or mixed red, blue, and green LEDs to create the display’s backlight. In the latter case, the panel’s color is theoretically improved because the backlight matches the color filters of the pixels themselves. Besides producing a wider color gamut, LED displays are also able to achieve a deeper black than standard CCFL monitors. On the other hand, LEDs are more expensive than CCFLs, and individual LEDs can, potentially, age at different rates.

Inputs

Increasingly, LCD monitors sport newer video
interfaces, such as HDMI, alongside the trusty
DVI port.

Ideally, you’re not planning to connect your new LCD monitor with a VGA cable. That analog standard is old and moldy, and it’s preferable to maintain a digital signal from your computer to the display. While LCD displays should come with at least one DVI port, that standard is being augmented by newer, more capable digital interfaces such as HDMI and DisplayPort.

Both offer greater bandwidth than DVI (which is crucial for displays with resolutions greater than 1920x1200), HDCP-support for playing copy-protected content, and the ability to carry both video and audio signals over the same thin cable. While HDMI has more market penetration on videocards than DisplayPort, adapters will allow you to connect your videocard’s DVI port to your display’s HDMI or DP input.

HDCP

Put simply, if your display doesn’t support HDCP (High-Definition Copy Protection), you won’t be able to watch commercial HD DVD or Blu-ray movies in full resolution on your display.

Contrast Ratio

Don’t pay attention to contrast ratios: They’re all hype, as each display manufacturer will engineer its own testing situation, so there’s no basis for meaningful comparison.

Manufacturers have recently taken to touting a screen’s dynamic contrast ratio, which is typically a higher (thus more impressive) number than standard contrast ratio, although the techniques for measuring this are just as suspect.

Some monitors offer a dynamic contrast feature that performs on-the-fly adjustments to contrast in order to enhance the grayscales of the given content. The downside is that these adjustments aren’t always analyzed correctly—your picture can be thrown too far into either the dark or light extreme. Worse, if consecutive scenes in a movie or game differ dramatically, you’ll likely notice the image fading in and out as the display adjusts to the content.

Pixel Response Time

Quite simply, pixel response time refers to how long it takes a single pixel to transition from one state to another. Just like contrast ratios, pixel response measurements are entirely at the mercy of the manufacturer. A slow pixel response time can result in ghosting in fast-moving content such as games.

Know Your Panel’s Lineage

While all modern LCD monitors fall under the thin-film-transistor (TFT) classification, subsets within that class bear notable differences. These are the most common types of TFTs:

• TN (Twisted Nematic): The most inexpensive and commonly used TFT, TN panels are known for having extremely fast pixel response times and a 6-bit color depth. These panels feature inferior viewing angles and lower color fidelity than S-IPS or S-PVA panels.
• S-IPS (Super In-Plan Switching): Considered to be the best overall TFT in terms of color reproduction and viewing angle, S-IPS panels are often sold at premium prices, so they’re sold by a limited number of manufacturers. The panels have 8-bit color depth, although black and dark grays can take on a purplish hue at wide viewing angles. And the overdrive technology manufacturers use to elicit faster pixel response times from these panels can introduce noise into videos, unless your monitor or videocard comes with a built-in noise-reduction function.
• S-PVA (Super Patterned- ITO Vertical Alignment): S-PVA panels also have 8-bit color depth and better color reproduction and viewing angles than TN panels. S-PVA panels feature better contrast and black levels than both TN and S-IPS panels, and S-PVA is usually the panel type found in higher-quality (but not professional) monitors.       

On To The Monitors!

• Planar  PL2210MW
• Gateway HD2201
• Envision G2219w1
• ViewSonic VX2240w
• Gateway FHD2401
• Acer P244w
• Samsung 245T
• Dell 2408WFP
• Hannspree HF28HJB
• Westinghouse L2610NM

Next Page: Multi-Monitor Mayhem!