Making the Switch from CRT to LCD Displays

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Most new and upgrade systems now call for flat-screen, narrow-profile LCDs rather than old-school, big and bulky CRT displays. But switching over from CRT to LCD is harder than it might seem. System builders need to understand the changes that accompany the switch from picture tubes to a liquid crystal displays.

Also, setup and key adjustments are more complicated with LCDs—and much more necessary—than they are with CRTs. To be sure, all displays can benefit from proper tuning and adjustment. But LCDs are more likely to experience clarity or viewability issues if they're not tuned and tweaked to optimum conditions.

In this Recipe, we'll tackle the system-building differences between LCDs and CRTs. We'll also describe the kinds of usage situations best suited to one kind of display over the other. Finally, we'll describe some important tools you can use to make sure your customers get the most from their LCD choices.

CRT vs. LCD: The Pros and Cons

We'll start with the pros and cons of CRT displays, and then do likewise for LCDs. After that, we'll make some comparisons and explain which type of display is best-suited for specific, identifiable usage scenarios.

Our comparison of the pros, cons, and differences between CRT and LCD displays hinges on the differences between analog and digital technologies. CRTs are analog; therefore, they support continuous values, smooth scaling, and arbitrarily high resolutions (within reason or the limits of technology). LCDs are digital and therefore work like an array of individual, discrete pixels with individual, discrete color and gray-scale values, and a fixed, native resolution. In mathematical terms, it's the difference between a continuous integral versus a stair-step function. Here's how they line up:

CRT Pros and Cons

Pros include:

• Black-level and contrast: CRTs produce dark blacks and high contrast levels. They may be used in dimly lit or dark environments.
• Color/gray-scale accuracy: Best color and gray scale accuracy; used as reference standard for professional calibration. Perfectly smooth gray-scale with infinite number of intensity levels.
• Cost: CRTs remain the least expensive of computer display technologies.
• Motion artifacts: The faster images move on a display, the more past display values can affect current display contents; these leftovers are called motion artifacts. CRTs offer fast response times with no motion artifacts. For this reason, CRTs are the best choice for fast-moving or ever-changing images.
• Resolution: CRTs operate at any resolution, geometry, and aspect ratio with no need to rescale images shown. CRTs also run at the highest resolutions graphics cards support.

The Cons include:

• Emissions: CRTs emit electrical, magnetic, and electromagnetic fields, where magnetic fields are often believed to pose health hazards (although no available scientific evidence supports this belief).
• Geometric distortion: CRTs are subject to geometric distortion and generally include adjustments to counter same. But they may also be affected by magnetic fields from other devices.
• Interference: CRTs produce visual distortions known as Moire patterns. While many monitors offer Moire reduction, this doesn't entirely eliminate this problem.
• Screen Shape: Older CRTs may have rounded screens, leading to image distortion in the corners. Newer CRTs are relatively flat.
• Sharpness: CRTs use electron beams to activate pixels on their screens. This results in softer images than an LCD operating at its native resolution. (But a CRT is usually sharper than an LCD not operating at its native resolutions.)
• Size, weight, and power consumption: CRTs are big and bulky. They consume more power—and give off more heat—than most other display technologies.

LCD Pros and Cons

The Pros include:

• Brightness: The high peak intensity of an LCD outputs bright images that work well in brightly lit environments.
• Geometric distortion: Zero at native resolution, and minor at other resolutions because of rescaling effects.
• Screen shape: LCD screens are as flat as technology will allow.
• Sharpness: Image is completely sharp at native resolution, but LCDs using analog inputs demand careful adjustment for pixel tracking and phase.
• Size, weight, and power consumption:LCDs are thin-profile devices that are generally lighter than CRTs. LCDs also consume less electricity—and give off less heat—than CRTs.

The Cons include:

• Aspect ratio: Any LCD has a fixed resolution and aspect ratio. For panels with a resolution of 1280 x 1024 (common for 17- and 19-inch models), the aspect ratio is 5:4 or 1.25, smaller than the 4:3 or 1.33 ratio common for other displays. This may require letterboxing to a 1280 x 960 resolution to get a standard 4:3 ratio.
• Bad pixels and screen uniformity: LCDs may include malfunctioning pixels that are weak, or stuck in on or off modes. They are also subject to variations in backlighting, owing to the use of light sources at the top or bottom edges of the display.
• Black-level, contract, color saturation: LCDs are poor at producing deep blacks and dark grays. This results in lower contrast and reduced color saturation for low intensity colors, which makes LCDs a poor choice for dimly lit or dark environments.
• Color and gray scale accuracy: Internal gamma and gray-scale on an LCD varies by location on the display surface. LCDs normally produce only a limited number—fewer than 256—of discrete intensity levels. This leads to image-accuracy issues with black level, gray-scale, and gamma, and it isn't suitable for professional color balancing.
• Cost: LCDs cost more—often twice as much or more—than CRTs with comparable diagonal measurements.
• Interference: LCDs using analog input require painstaking adjustment of pixel tracking and phase to minimize digital noise in image display. Automatic controls seldom produce optimum outputs, and it may be impossible to eliminate all digital noise completely.
• Motion artifacts: The slower an LCD's pixel refresh rate—often called response time, though this term is more appropriate for CRTs—the more likely it is that motion artifacts will appear. For continuous or very fast motion, some artifacts are inevitable on an LCD.
• Resolution: Native resolution is set by the manufacturer and cannot be altered. All other resolutions require re-scaling and leads to image degradation, especially where fine text and graphics are concerned.
• Viewing angle: Viewing angle affects brightness, contract, gamma, and color mixtures. Head-on viewing produces the best results.
• White saturation: White levels on LCDs are easily overloaded, and maximum brightness occurs before gray-scale values peak. This phenomenon is best managed by careful contrast-setting adjustments.