Performance characteristics of monitors

The performanceof a monitor is measured in the following parameters:

· Brightness - the luminance of images is measured in cd/m2 (candela per square metre).

· Screen size (viewable image size)is measured diagonally, in other words, a 17" screen measures 17 inches from the top left corner to the bottom right. For CRTs, the viewable size is typically one inch (25 mm) smaller than the tube itself.

· Resolution- the clarity of the image depends on the number of distinctpixelscontained on a display, horizontally and vertically. A typical resolution is 1024 x 768. The sharpness of images is affected by dot pitch, the distance between the pixels of the same color on the screen, so a dot pitch of 0.28 mm or less will produce a sharp image. Maximum resolution is limited by dot pitch: the smaller the dot pitch, the sharper the picture will appear.

· Colour depth - the number of colours a monitor can display. For example, a VGA monitor produces 256 colours, enough for home use; a SuperVGA can produce up to 16.7 million colours, so is ideal for photographic work and video games.

· Refresh rate is the number of times in a second that a display is illuminated. If a monitor has a refresh rate of 75 Hertz (Hz), it means that the screen is scanned 75 times per second. If this rate is low, you will notice a flicker, which can cause eye fatigue. Maximum refresh rate is limited by response time.

· Response time is the amount of time a pixel in a monitor takes to go from active (black) to inactive (white) and back to active (black) again. It is measured in milliseconds. Lower numbers mean faster transitions and therefore fewer visible image artifacts.

· Contrast ratio is the ratio of the luminosity of the brightest color (white) to that of the darkest color (black) that the monitor is capable of producing.

· Power consumption is measured in watts.

· Aspect ratio is the ratio of the horizontal length to the vertical length. 4:3 is the standard aspect ratio, for example, so that a screen with a width of 1024 pixels will have a height of 768 pixels. If a widescreen display has an aspect ratio of 16:9, a display that is 1024 pixels wide will have a height of 576 pixels.

· Viewing angle is the maximum angle at which images on the monitor can be viewed, without excessive degradation to the images. It is measured in degrees horizontally and vertically.