Bits for pictures. Performance characteristics of monitors

Sound output

Computer speakers, or multimedia speakers, are external speakers, commonly equipped with a low power internal amplifier. More sophisticated computer speakers may have a ' subwoofe r' unit to enhance bass output. Laptops come with integrated speakers. For some users, a lead connecting computer sound output to an existing stereo system is practical. This normally yields much better results than small low-cost computer speakers.

Headphones are a pair of small loudspeakers, or less commonly a single speaker, with a way of holding them close to a user's ears and a means of connecting them to a signal source. They are also known as earphones, earbuds, stereophones, headsets or, informally cans.

The characters and pictures that we see on the screen are made up of dots, also called picture elements (pixels).

In a bit-mapped display, the dots displayed on the screen correspond, pixel by pixel, with bits in the main memory of the computer. The bits are held in an area of the memory called the 'refresh buffer' and are stored in groups that represent the horizontal and vertical position of the pixels on the screen and whether the pixels are on or off. On monochrome systems, one bit in this 'map' represents one pixel on the screen and can be either 'on' or 'off' (black or white). On colour systems, each pixel is a certain combination of the three primary colours: red, green and blue. The total number of colours which can be shown on the screen is called the colour palette

The performance of a monitor is measured in the following parameters:

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

 Screen size (v iewable 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 distinct pixels contained on a display, horizontally and vertically. A typical resolution is 1024 x 768.

 Colour depth - the number of colours a monitor can display.

 Refresh rate is the number of times in a second that a display is illuminated.

 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

 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.

 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.

Дата добавления: 2015-05-29