Aperture grill/shadow mask
All monitors have an aperture grill or shadow mask, a piece of thin, perforated metal through which electron beams pass before striking phosphors. While most picture tubes use a dot mask, one with very small holes, Sony's Trinitron picture tubes use a mask with long vertical slots. The geometry of the openings of the masks prevent the electron beams from striking the wrong phosphor dots. The electron beam for red is blocked from illuminating blue phosphors by the mask; in other words, the mask creates a shadow over the blue and green dots when the beam for red passes.
Blooming
Blooming
occur
s when the image on a monitor appears to grow in size when that image is brightly illuminated. You will see this most often with bright white characters or objects. Characters become unfocused as the pixels spread and defuse.
Convergence/misconvergence
Monitors use the RGB color model, producing white by illuminating the three phosphor dots of a color triad simultaneously. Convergence is a monitor's ability to precisely illuminate each dot in the triad. This is difficult because the electron beams for RGB must converge exactly on each triad. Misconvergence occurs when the electron beams scan the wrong dots of a triad and manifests itself as colored edges on white objects. High levels of misconvergence appear as shifted colors.
Dot pitch
Dot pitch refers to the distance between the centers of RGB phosphor dots that make up the color triad. Smaller distances generally mean greater resolution capability. Comparing a monitor with a .53-mm dot pitch to one with
a .28-mm dot pitch is similar to comparing a 9- and 24-pin printer. In products using the Trinitron aperture grill, the dot pitch refers to the center-to-center distance of the vertical grill openings.
Horizontal frequency
This indicates the number of horizontal lines illuminated on-screen in 1 second. Increasing resolution requires greater horizontal frequency.
Vertical refresh rate
The speed at which the electron beams scan across the screen from top to bottom is the vertical refresh rate. The beam of electrons sweeps across the phosphor dots a line at a time. The phosphor absorbs the energy of the beam and releases this energy as light. As the energy is used, the light fades. If the beams do not return to the phosphor dots quickly enough, the image starts to fade. This results in a visual effect called flicker. High refresh rates reduce flicker and keep the image sharp and stable. As resolutions increase, the need for higher refresh rates also goes up.
Higher resolutions require more and smaller pixels, and to prevent image degradation, they must be refreshed more often.
Interlaced/noninterlaced
In
interlaced
mode, the display image is divided into two fields consisting of either odd or even scan lines. On one pass, the electron beams refresh the even lines, and then on the next pass, they refresh the odd lines.
Noninterlaced
means the electron beams scan every line of the display on each vertical sweep. Manufacturers developed interlacing as a way of pushing higher resolutions through the narrow bandwidth of early displays and video adapters. Products that support greater signal bandwidth do not need to interlace. You should consider only the maximum noninterlaced resolution when evaluating monitors.
Degaussing
Strong electromagnets control the deflection of the electron beams used to illuminate phosphors. These electromagnets are susceptible to interf
erence from the earth's magnetic field. As you pan or tilt the monitor, you pass it through these magnetic fields, which can cause the monitor to display color shifts or blotches of discoloration. The degauss control realigns the electron beams and reduces screen discoloration.
Multiscanning vs. fixed frequency
A multiscanning monitor has the ability to lock on to virtually any frequency between the high and low limits of its controlling electronics. A fixed-frequency monitor will accept video signals at one of a limited number of combinations that must match the signals the display adapter provides. All the products in this review offer multiple-frequency synchronization.
Resolution
The size of the pixels contributes to the sharpness of the image and the amount of an image displayed. Increasing resolution requires more and smaller pixels. Standard VGA resolution is 640 pixels horizontally and 480 pixels vertically. We tested monitors capable of resolution
s as high as 1600 pixels by 1280 pixels. Increasing the resolution means sending more data; consequently, monitors offering high resolutions must also provide greater bandwidth. High-resolution modes also require faster refresh rates.
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Key Terms
