September 1998

Increase Your View

Sit yourself down in front of a 20" or 21" monitor and you'll wonder how you ever worked without one. We put 9 of the latest models through their paces and explain what to look for in a high-end monitor.

Some also feature flatter CRT screens that reduce geometric distortion and glare. The newest innovation is the totally flat CRT monitor. The tube is designed with undetectable curvature of the front glass. Flat screens can produce a concave look, which is why some have very slight curvatures. Flat screen monitors are offered by Panasonic, Sony and Mitsubishi and they are more expensive than traditional CRTs.

We looked at a total of nine monitors including one 20" model and eight 21" displays. Our test relied on DisplayMate software for Windows 95 from Sonera Technologies (Rumson, NJ 732-747-6886). DisplayMate is a program that generates various test patterns that are used to set up monitors and make fine adjustments to settings. The $79 program provides descriptions of what to look for with each test pattern, and it tells you how you can make adjustments to monitor settings to improve performance.

DisplayMate can also be used to evaluate LCD monitors, graphics boards and video systems. It comes on a disk that you can take with you to the store when shopping for a new monitor. Go to www.displaymate.com for tips on monitor selection and downloadable test demos.

In our test we selected from DisplayMate's test patterns and created our own Imaging Magazine test script. A total of 21 different test patterns were used on each monitor. We tested for:

Average Picture Level (APL): A higher intensity of white raises the APL and can affect the intensities of black and grays.

Black Level: The monitors should be able to produce a true black while also handling the most subtle variations or scales of gray.

Color Balance and Convergence: A monitor uses three electron guns (one each for red, green and blue) to excite the phosphors that make up the pixels in an image. If one gun is turned up higher than the other two, you will get a color imbalance and see a tint on the screen. The three CRT beams must also converge precisely on the phosphors to produce a single color image without loss to image detail.

Color Saturation and Tracking: Monitors should be able to display gradations of color intensity without altering tint. A monitor with good color saturation can display slight change in color distinctly. Color tracking refers to a monitor's ability to keep all three electron guns operating at equal strength when displaying different brightness levels.

Focus, Contrast and Legibility: Various images were used to test the legibility of text at various point sizes on white and black backgrounds. Images should appear in focus from the center of the screen to the corners. There should be a minimum of color streaking and halo, which undermine contrast.

Geometry: This refers to the monitor's ability to reproduce various shapes accurately and without distortion. Problems with geometry include pincushion, trapezoid, rotation (or tilt) and poor linearity.

Moiré: These are undesirable wavy lines or ripples that are a common occurrence in CRT displays due to natural interference. This is sometimes intensified in high-resolution monitors with very finely focused beams.

Screen Regulation: The effects of brightness on image expansion and contraction. A higher intensity of white can cause images to expand.

Screen Uniformity: When displaying a solid color, the screen should look the same from the center to the corners without dark spots.

Video Bandwidth: This is the monitor's ability to refresh the screen. High bandwidths allow more information to be painted across the display in a given amount of time, which translates into support for higher resolutions and higher refresh rates.

White Level Saturation: The brightest whites should not be saturated and the monitor should be able to display a range of white intensities.

Finally we looked at the overall design, which boils down to a lot of time spent playing with monitor's controls and looking at the design. The latest monitors are loaded with controls that let you adjust and correct problems in the image. The controls to look for are brightness, contrast, size and position.

Most of the monitors we tested also included controls for focus, convergence, tilt, pincushion, moiré, color temperature and manual degaussing. Degaussing is used to correct problems with color purity resulting from magnetic fields that can build up within the monitor.

Some models had more advanced controls for color purity, dynamic focus, dynamic convergence, pincushion phase and pincushion balance. The more controls you have, the more you can fine-tune the image and picture quality.

Choose a Design

There are many specifications you should consider when buying a monitor. The first decision to make is shadow mask or aperture grille. These are two different types of monitors.

Shadow mask monitors use a metal plate with holes in it to direct the beams from the red green and blue electron guns at the back of the tube. The holes in the plate focus the beams from the electron guns at the back of the CRT. The newer slot mask monitors are similar to shadow mask. Both of these types of monitors produce sharp text and are well suited for document imaging and office applications.

Aperture grille monitors use a series of wires that run vertically down the inside of the CRT to perform the same function as the metal plate with holes in shadow mask monitors. Aperture grille monitors are used in image editing and desktop publishing because they generate brighter colors than shadow mask or slot mask monitors.

One way to tell if you are looking at an aperture grille monitor is the presence of one or two very thin black horizontal lines that cross the screen when you look closely; these lines are the supports for the aperture grille.

The main difference between aperture grille, shadow mask and slot mask monitors is the different phosphor pixels or beam shape produced by the varying tube designs. An aperture grille shapes the beam into vertical lines, shadow mask to circles and slot mask to ovals.

Don't Dwell on Dot Pitch

The monitor screen is made up of groups of tiny red, green and blue phosphors, called triads, that produce colored light patterns that make up an image. The dot pitch is the spacing between the groups, expressed in millimeters. Values for the monitors covered here range between 0.22 and 0.27 mm. The smaller the value, the finer and sharper the image can be. Anything over 0.32 mm will begin to look grainy. But directly comparing dot-pitch values is not a reliable way to determine which monitor is better.

While dot pitch specifications are provided here in the product descriptions, you might be better off ignoring these numbers. The dot pitch depends on the tube design, which varies from manufacturer to manufacturer. A 0.25 mm pitch for one monitor may not be as good as 0.30 mm for another.

Making things even more confusing is that there is more than one specification for pitch size. There is horizontal pitch, which is the distance between triads that are on the same horizontal row. And there is vertical pitch, which is always different from the horizontal pitch. The one used to specify a monitor's dot pitch also depends on the tube design. For a shadow mask pitch the vertical pitch is used while for an aperture grille pitch the horizontal pitch is used. For a slot mask pitch either one may be used.

Check Resolution and Refresh Rate

High resolution is desirable, but it can have an adverse effect on the refresh rate. The refresh rate is the measurement of times per second a screen is redrawn by the electron guns at the back of the CRT. This is measured in Hertz (Hz). High resolution can lower the refresh rate because the beams have to redraw more information per second. A slow refresh rate will cause the screen to flicker.

As a rule, refresh rates of less than 75 Hz can cause eye fatigue. Running a monitor at a high refresh rate of about 85 Hz will ensure flicker-free performance with reduced eyestrain.

One gauge of a monitor's combined resolution and refresh rate performance is horizontal scan frequency, which is provided in most monitor specifications. Horizontal scan frequency is the time it takes to draw one line of pixels, measured in Kilohertz (kHz). To run at 1,600 x 1,200 resolution with a refresh rate of 85 Hz, you would need a 106 kHz horizontal scan frequency. (Refer to our Horizontal Frequency Chart )

Monitor manufacturers also specify "viewable area," which is the actual size of monitor's display. This can be anywhere from 1" to 1.5" less than the monitor size. The larger the viewable area the better.

All of these monitor specifications are important. However, choosing a monitor is a very subjective process. There is no substitute for your own two eyes. The best way to purchase a monitor is to view them in person if possible. Have your vendor come to your office with samples or go to a store to see some models first hand before placing an order. Make sure your monitor is covered by a manufacturer's warranty. All of the monitors covered here came with at least three years limited on parts and labor. Some also have special unit replacement plans that can save you in a crisis.

Related Articles:

• Hitachi/MSA Superscan 812
• NEC MultiSync P1250+
• Nokia 445XiPlus
• More On Our Test Procedure
• Pacific Technology ArtMedia GT-960T
• Panasonic PanaSync/Pro P110
• Sampo KM-950S
• Samsung SyncMaster 1000p
• Sony GDM-500PS
• ViewSonic P815