Monitors
Monitor
LCD computer monitors in a computer lab
A computer monitor is an output device which displays information in pictorial form. A monitor usually comprises the display device,circuitry, casing, and power supply. The display device in modern monitors is typically a thin film transistor liquid crystal display(TFT-LCD) with LED backlighting having replaced cold-cathode fluorescent lamp(CCFL) backlighting. Older monitors used acathode ray tube (CRT). Monitors are connected to the computer via VGA, Digital Visual Interface (DVI), HDMI, DisplayPort,Thunderbolt, low-voltage differential signaling(LVDS) or other proprietary connectors and signals.
Originally, computer monitors were used fordata processing while television receiverswere used for entertainment. From the 1980s onwards, computers (and their monitors) have been used for both data processing and entertainment, while televisions have implemented some computer functionality. The common aspect ratio of televisions, and computer monitors, has changed from 4:3 to 16:10, to 16:9.
History
Technologies
Multiple technologies have been used for computer monitors. Until the 21st century most used cathode ray tubes but they have largely been superseded by LCD monitors.
Cathode ray tube
The first computer monitors used cathode ray tubes (CRTs). Prior to the advent of home computers in the late 1970s, it was common for a video display terminal (VDT) using a CRT to be physically integrated with a keyboard and other components of the system in a single large chassis. The display wasmonochrome and far less sharp and detailed than on a modern flat-panel monitor, necessitating the use of relatively large text and severely limiting the amount of information that could be displayed at one time. High-resolution CRT displays were developed for the specialized military, industrial and scientific applications but they were far too costly for general use.
Some of the earliest home computers (such as the TRS-80 and Commodore PET) were limited to monochrome CRT displays, but color display capability was already a standard feature of the pioneering Apple II, introduced in 1977, and the specialty of the more graphically sophisticated Atari 800, introduced in 1979. Either computer could be connected to the antenna terminals of an ordinary color TV set or used with a purpose-made CRT color monitor for optimum resolution and color quality. Lagging several years behind, in 1981 IBM introduced theColor Graphics Adapter, which could display four colors with a resolution of 320 x 200 pixels, or it could produce 640 x 200 pixels with two colors. In 1984 IBM introduced theEnhanced Graphics Adapter which was capable of producing 16 colors and had a resolution of 640 x 350.[1]
By the end of the 1980s color CRT monitors that could clearly display 1024 x 768 pixels were widely available and increasingly affordable. During the following decade, maximum display resolutions gradually increased and prices continued to fall. CRT technology remained dominant in the PC monitor market into the new millennium partly because it was cheaper to produce and offered to view angles close to 180 degrees.[2]CRTs still offer some image quality advantages[clarification needed] over LCDs but improvements to the latter have made them much less obvious. The dynamic range of early LCD panels was very poor, and although text and other motionless graphics were sharper than on a CRT, an LCD characteristic known as pixel lag caused moving graphics to appear noticeably smeared and blurry.
Liquid crystal display
There are multiple technologies that have been used to implement liquid crystal displays (LCD). Throughout the 1990s, the primary use of LCD technology as computer monitors was in laptops where the lower power consumption, lighter weight, and smaller physical size of LCD's justified the higher price versus a CRT. Commonly, the same laptop would be offered with an assortment of display options at increasing price points: (active or passive) monochrome, passive color, or active matrix color (TFT). As volume and manufacturing capability have improved, the monochrome and passive color technologies were dropped from most product lines.
The first standalone LCDs appeared in the mid-1990s selling for high prices. As prices declined over a period of years they became more popular, and by 1997 were competing with CRT monitors. Among the first desktop LCD computer monitors was the Eizo L66 in the mid-1990s, the Apple Studio Display in 1998, and the Apple Cinema Display in 1999. In 2003, TFT-LCDs outsold CRTs for the first time, becoming the primary technology used for computer monitors.[2] The main advantages of LCDs over CRT displays are that LCD's consume less power, take up much less space, and are considerably lighter. The now common active matrix TFT-LCD technology also has less flickering than CRTs, which reduces eye strain.[4] On the other hand, CRT monitors have superior contrast, have a superior response time, are able to use multiple screen resolutions natively, and there is no discernible flicker if the refresh rate is set to a sufficiently high value. LCD monitors have now very high temporal accuracy and can be used for vision research.[5]
High dynamic range (HDR) has been implemented into high-end LCD monitors to improve color accuracy. Since around the late 2000s, widescreen LCD monitors have become popular, in part due to television series, motion pictures and video gamestransitioning to high-definition (HD), which makes standard-width monitors unable to display them correctly as they either stretch or crop HD content. These types of monitors may also display it in the proper width, however they usually fill the extra space at the top and bottom of the image with black bars. Other advantages of widescreen monitors over standard-width monitors is that they make work more productive by displaying more of a user's documents and images, and allow displaying toolbars with documents. They also have a larger viewing area, with a typical widescreen monitor having a 16:9 aspect ratio, compared to the 4:3 aspect ratio of a typical standard-width monitor.
Organic light-emitting diode
Organic light-emitting diode (OLED) monitors provide higher contrast and better viewing angles than LCD's but they require more power when displaying documents with white or bright backgrounds. In 2011, a 25-inch (64 cm) OLED monitor cost $7500, but the prices are expected to drop.[6]
Measurements of performance
The performance of a monitor is measured by the following parameters:
- Luminance is measured in candelas per square meter (cd/m2 also called a Nit).
- Aspect ratio is the ratio of the horizontal length to the vertical length. Monitors usually have the aspect ratio 4:3, 5:4, 16:10or 16:9.
- Viewable image size is usually measured diagonally, but the actual widths and heights are more informative since they are not affected by the aspect ratio in the same way. For CRTs, the viewable size is typically 1 in (25 mm) smaller than the tube itself.
- Display resolution is the number of distinct pixels in each dimension that can be displayed. For a given display size, maximum resolution is limited by dot pitch.
- Dot pitch is the distance between sub-pixels of the same color in millimeters. In general, the smaller the dot pitch, the sharper the picture will appear.
- Refresh rate is the number of times in a second that a display is illuminated. Maximum refresh rate is limited by response time.
- Response time is the time a pixel in a monitor takes to go from active (white) to inactive (black) and back to active (white) again, 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.
- Delta-E: Color accuracy is measured in delta-E; the lower the delta-E, the more accurate the color representation. A delta-E of below 1 is imperceptible to the human eye. Delta-Es of 2 to 4 are considered good and require a sensitive eye to spot the difference.
- Viewing angle is the maximum angle at which images on the monitor can be viewed, without excessive degradation to the image. It is measured in degrees horizontally and vertically.
Size
The area, height and width of displays with identical diagonal measurements vary dependent on aspect ratio.
On two-dimensional display devices such as computer monitors the display size or view able image size is the actual amount of screen space that is available to display apicture, video or working space, without obstruction from the case or other aspects of the unit's design. The main measurements for display devices are: width, height, total area and the diagonal.
The size of a display is usually by monitor manufacturers given by the diagonal, i.e. the distance between two opposite screen corners. This method of measurement is inherited from the method used for the first generation of CRT television, when picture tubes with circular faces were in common use. Being circular, it was the external diameter of the glass envelope that described their size. Since these circular tubes were used to display rectangular images, the diagonal measurement of the rectangular image was smaller than the diameter of the tube's face (due to the thickness of the glass). This method continued even when cathode ray tubes were manufactured as rounded rectangles; it had the advantage of being a single number specifying the size, and was not confusing when the aspect ratio was universally 4:3.
With the introduction of flat panel technology, the diagonal measurement became the actual diagonal of the visible display. This meant that an eighteen-inch LCD had a larger visible area than an eighteen-inch cathode ray tube.
The estimation of the monitor size by the distance between opposite corners does not take into account the display aspect ratio, so that for example a 16:9 21-inch (53 cm)widescreen display has less area, than a 21-inch (53 cm) 4:3 screen. The 4:3 screen has dimensions of 16.8 in × 12.6 in (43 cm × 32 cm) and area 211 sq in (1,360 cm2), while the widescreen is 18.3 in × 10.3 in (46 cm × 26 cm), 188 sq in (1,210 cm2).
Aspect ratio
Until about 2003, most computer monitors had a 4:3 aspect ratio and some had 5:4. Between 2003 and 2006, monitors with 16:9and mostly 16:10 (8:5) aspect ratios became commonly available, first in laptops and later also in standalone monitors. Reasons for this transition was productive uses for such monitors, i.e. besides widescreen computer game play and movie viewing, are the word processor display of two standard letter pages side by side, as well as CAD displays of large-size drawings and CAD application menus at the same time.[7][8] In 2008 16:10 became the most common sold aspect ratio for LCD monitors and the same year 16:10 was the mainstream standard for laptops andnotebook computers.[9]
In 2010 the computer industry started to move over from 16:10 to 16:9 because 16:9 was chosen to be the standard high-definition television display size, and because they were cheaper to manufacture.
In 2011 non-widescreen displays with 4:3 aspect ratios were only being manufactured in small quantities. According to Samsung this was because the "Demand for the old 'Square monitors' has decreased rapidly over the last couple of years," and "I predict that by the end of 2011, production on all 4:3 or similar panels will be halted due to a lack of demand."[10]
Resolution
The resolution for computer monitors has increased over time. From 320x200 during the early 1980s, to 800x600 during the late 1990s. Since 2009, the most commonly sold resolution for computer monitors is 1920x1080.[11] Before 2013 top-end consumer LCD monitors were limited to 2560x1600 at 30 in (76 cm), excluding Apple products and CRT monitors.[12] Apple introduced 2880x1800 with Retina MacBook Pro at 15.4 in (39 cm) on June 12, 2012, and introduced a 5120x2880 Retina iMac at 27 in (69 cm) on October 16, 2014. By 2015 most major display manufacturers had released 3840x2160 resolution displays. I
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