Making the Switch from CRT to LCD 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
- 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.
Advice for Your Customers
When it comes to picking one kind of display over the other, here's what you should advise your customers on a number of criteria, including needs, pocketbooks, and working environments:
- Color or gray-scale accuracy: Users who need or want higher color or gray-scale accuracy, and more viewable deep blacks or dark grays, will be better served by CRTs. Professional color balancing demands a high-quality CRT.
- Contrast: CRTs produce the brightest contrast levels available, LCDs fare somewhat more poorly, especially with black and dark colors. Contrast ratio numbers published for LCD displays cannot always be taken literally.
- Environmental concerns: CRTs, especially the picture tube itself, are chock-full of heavy metals of several varieties and pose more challenges for recycling than do LCDs. Also, smaller size and weight means less waste to manage. Also, LCDs emit less heat and other forms of energy—electrical, electromagnetic and magnetic—than do CRTs.
- Footprint: For equivalent resolutions, LCDs typically require one-third or less as much 2D and 3D space as CRTs.
- Lighting: Users who work in bright light are bound to prefer an LCD. Users who work in lower-light conditions will increasingly prefer a CRT as ambient light decreases.
- Motion and artifacts: Users who need or want to work with fast or constantly moving images are best served by CRTs. But this also limits diagonal sizes to no more than 24 inches.
- Operating costs: Those concerned about energy consumption will favor LCDs, as these monitors consume at least 40 percent less electricity than CRTs with the same rated diagonal measurements. (And standby mode savings are about 40 percent.) In theory, users can also get away with less office space by using LCDs, translating into lower rent.
- Purchase cost: Those with smaller budgets should consider CRTs, as they cost 50 percent or less than LCDs with the same reported diagonal measurements.
- Resolution: If a user doesn't like an LCD at its native resolution, this spells trouble. Native resolution for an LCD is equivalent to maximum resolution on a CRT; it represents the upper limit of picture quality for a given model. So if a user needs a monitor to run at multiple resolutions, especially if they also need fine text and graphics for all resolutions, this virtually mandates a CRT.
Tools for Working with LCD Displays
With more customers switching to LCDs, system builders should understand how to set up these monitors and configure them properly once they're in place. A system builder should also know how to get the best-looking text on the screen. To help, we'll now describe some great tools for system builders working with LCD displays.
ClearType is a Microsoft technology specifically designed to improve text readability on LCD screens, including laptop screens, mobile device displays, and flat-panel monitors. ClearType technology can access individual color elements in each pixel on an LCD display. Prior to its introduction, the level of detail operated at the pixel level. But with ClearType running on an LCD monitor, features of text as small as a fraction of a pixel in width can be displayed, according to Microsoft. This leads to a visible improvement in the sharpness of tiny text details. It not only improves readability, but also is easier on the eyes, especially over extended periods of time.
ClearType is included with Windows XP. But to tweak text settings on individual LCD displays, you must download a Windows PowerToy called ClearType Tuner.
Once downloaded and installed, ClearType Tuner appears as a control panel widget named ClearType Tuning. Its users work with a wizard that asks them to select among multiple on-screen displays that look the best, in much the same way an optometrist works with patients to help determine a new prescription for corrective lenses.
As shown below, the ClearType Tuning widget asks you to run a wizard to tune ClearType Settings:
As depicted here, the ClearType Tuning wizard has you pick through a series of text displays to tweak readability:
Using the ClearType Tuning widget is fast and easy, and a bit of practice makes working with it a snap. You'll also see noticeable improvements to text on LCD screens as a consequence of its use, as toggling the check box for "Turn on ClearType" in the widget itself will show.
DisplayMate Technologies is a small and highly-regarded company that offers a family of powerful tools of great interest to system builders and consultants. The company offers a $89 (download only) or $99 (CD and manual shipped to buyer) product called DisplayMate for Windows Video Edition, which we highly recommend. It not only supports both CRT and LCD displays, but also other display types, including liquid crystal on silicon (LCoS), digital light processing (DLP), TV, HDTV, Plasma, and multi-media displays. Though this product aims primarily at end-users and consumers, system builders and consultants on a tight budget can get plenty of value from this product.
System builders who work with lots of displays and really want to get the most out of them will probably prefer the higher end DisplayMate Multimedia Edition, which sells for $495. It not only handles the same kinds of displays as the aforementioned Windows Video Edition, but also includes many more test patterns and command scripts to perform customized display testing and tuning.
This scaffolding around the consumer-level DisplayMate for Windows program provides users with a set of detailed descriptive text screens that precede each of the monitor test sequences under two general headings: Set-Up Program and Tune-Up Program.
The Set-Up program helps familiarize users with graphics and display capabilities on the systems under test, and to establish initial configuration. The Tune-Up Program provides quick checks on specific display capabilities, with opportunities to tweak and tune them for optimal display output.
Five Points of the DisplayMate Set-Up Program
The options for the DisplayMate's Set-Up Program heading are:
- Introduction: A lead-in screen for the program that briefly describes its capabilities and (more important) provides the option to toggle the Novice Option on or off. Beginners will appreciate its information and instructions, while experienced users can ignore this.
- Set-Up Display: A stepwise procedure that leads users through all available user controls on their display and graphics card, each of which is associated with a test pattern and an explanation of how to use its appearance on screen to achieve settings that are visually optimal. First, an initial explanation appears on screen. Then, users click through a sequence of 22 test-pattern screens that include checks on brightness and contrast, intensity range, black-level, and gray scale checks, numerous standard test patterns and color gauges, and numerous geometry checks. The whole sequence takes at least 30 minutes to traverse the first few times through, especially if you read all the preliminary text that precedes each individual test (and if our experience is any guide, you definitely should).
- Video Obstacle Course: A set of demanding and difficult images designed to stress test displays and show settings in need of adjustment or improvement. The software also provides information about what users will see during these 24 tests, and how to remedy any potential problems or issues they may expose. About a third of the tests repeat from the previous Set-Up Display sequence, but others deal with important checks related to Moire patterns, color registration, screen and local display regulation, and more. Expect to spend at least 30 minutes working through this series of test patterns and checks.
- Master Test Pattern: As the name suggests, this one has a little bit of everything: Geometry, focus and resolution checks, gray-scale and color levels and saturation, and more. You'll learn to use this to take a quick look at a display and see if it needs some (or more) work.
- Video System Information: Shows what information from your display and graphics card DisplayMate can read, including native resolution, screen colors, gray levels, screen and pixel aspect ratios, pixel shape (square or not), color depth, palette, and planes, as well as system font and display driver information. Useful to make sure everything is as it should be.
Five Steps for the Tune-Up Program
The DisplayMate Tune-Up Program includes the following elements, whose organization indicates that this tool takes a functional view of the various activities involved in display tuning and tweaking:
- Geometry and Distortion: This deals with positioning, linearity, and screen regulation issues. There are 12 tests or checks in all.
- Sharpness and Resolution: Deals with sharpness, focus, and resolution with numerous horizontal and vertical bars, as well as the battery of Moire pattern tests (18 in all).
- Screen Pixel Resolution: Shows a series of 15 visually interesting test patterns to check screen resolution, fineness of detail, and accuracy in a series of complex line and pattern traces. This is some of the coolest looking stuff in the program.
- Color and Gray-Scale: A series of 20 color and grayscale bar and block patterns designed to test display saturation, color capabilities, and more.
- Miscellaneous Effects: A series of 14 tests and checks that let you fool around with colors and gray scales on the display. Be sure to toggle through color selections where you can; click the right mouse button to toggle through such options where available.
In our test lab, we have a number of LCD screens ranging in size from 17 inches (diagonal) to 30 inches. We found the DisplayMate program's ability to help us properly set brightness, contrast, and pixel timing to be of greatest use. Those are the aspects of our LCDs that suffer the most when left at factory-default settings. System builders and consultants will find these tools useful in making sure that their customers and users have the best possible experiences when they upgrade or switch to LCD displays.
ED TITTEL is a freelance writer and trainer in Austin, TX, who specializes in Windows topics and tools, especially networking and security related matters. JUSTIN KORELC is a long-time Linux hacker and Windows maven who concentrates on hardware and software security topics. Ed and Justin are also co-authors of Build the Ultimate Home Theater PC (John Wiley, 2005).