The optical system and CRT tube constitute the projection tube, and the so-called three-gun projector is a projector composed of three projection tubes. The image displayed by CRT projector is rich in color, good in reducibility and rich in geometric distortion adjustment ability; Disadvantages are low brightness, complicated operation, huge volume and high requirements for installation environment.
CRT projectors have two unique performance indicators that deserve attention.
Convergence performance
Convergence refers to the overlap of red, green and blue colors on the screen.
For CRT projectors, convergence control is particularly important, because it has three kinds of CRT tubes, RGB, which are installed in parallel on the bracket. In order to achieve complete convergence of images, various image distortions must be corrected. With the change of machine position, the connection needs to be readjusted, so the requirements for connection are full-featured and convenient. Convergence includes static convergence and dynamic convergence, in which dynamic convergence has functions such as tilt, bow, amplitude, linearity, trapezoid and pillow, and each function can be adjusted in both horizontal and vertical directions. In addition, nonlinear balance, trapezoidal balance and pillow balance can be adjusted.
Focusing performance of cathode ray tube
As we all know, the smallest unit of a graph is a pixel. The smaller the pixel, the higher the resolution of the graph. In CRT kinescope, the minimum pixel is determined by focusing performance, and the so-called addressable resolution refers to the minimum number of pixels.
CRT tubes have three focusing mechanisms: electrostatic focusing, magnetic focusing and electromagnetic compound focusing. Among them, electromagnetic compound focusing is more advanced and has the advantages of good focusing performance, especially defocusing under high brightness and high focusing accuracy. It can focus on different areas, edges and corners, so that every point on the screen is clear.
LCD, the abbreviation of Liquid Crystal Display, is a digital display technology, which can filter the light source through liquid crystal and color filters to produce images on the flat panel. Compared with the traditional cathode ray tube (CRT), LCD has the advantages of small space, low power consumption, low radiation, no flicker and less visual fatigue. Disadvantages: Compared with CRT of the same size, it is more expensive.
After occupying a dominant position in the notebook computer market for many years, the smooth display screen based on LCD technology is gradually entering the desktop system market. LCD has many advantages that traditional CRT display technology does not have. It can provide clearer text display and no flicker on the screen, which can effectively reduce the visual fatigue caused by staring at the screen for a long time. The thickness of LCD is generally less than 10 inch. If the desktop system adopts LCD technology, it will save more space. Although LCD display has its attractive originality, it is undeniable that LCD still has some shortcomings in high-quality color display compared with its main competitor CRT display. In addition, the price gap makes LCD still a luxury enjoyed by only a few people.
As early as 1888, it was found that liquid crystal, like a metal in a magnetic field, will produce an accurate and orderly arrangement of its molecules when it is influenced by an external electric field. If the arrangement of molecules is properly controlled, liquid crystal molecules will let light pass through. Whether it is a notebook computer or a desktop system, the LCD screen used is a layered structure composed of different parts. The last layer is a backlight layer composed of fluorescent substances, which can emit light. The light emitted by the backlight layer enters the liquid crystal layer containing thousands of crystal droplets after passing through the first polarizing filter layer. The crystal droplets in the liquid crystal layer are all contained in a fine cell structure, and one or more cells constitute a pixel on the screen. When the electrodes in the liquid crystal display generate an electric field, the liquid crystal molecules will be distorted, so that the light passing through them will be refracted regularly, and then displayed on the screen after being filtered by the second filter layer.
For a simple monochrome LCD display, such as the display screen used in PDA, the above structure is enough. However, for the more complex color display used in notebook computers, it is also necessary to have a special color filter layer for color display. Generally, in a color LCD panel, each pixel consists of three liquid crystal cells, and each liquid crystal cell has a red, green or blue filter in front of it. In this way, different colors can be displayed on the screen by light from different cells. Now, almost all LCDs used in notebook or desktop systems use thin film transistors (TFT) to activate cells in the liquid crystal layer. TFT LCD technology can display clearer and brighter images. The early LCD was a passive light-emitting device with low speed, poor efficiency and small contrast. Although clear characters can be displayed, shadows often appear when images are displayed quickly, which affects the display effect of video. So it is only used for PDA, pager or mobile phone that needs black and white display.
Affected by the actual number of cells in the LCD layer, LCD displays can only provide a fixed display resolution. If users need to improve the resolution of 800X600 to 1024X768, the analog resolution can only be achieved with special software.
Like the traditional CRT display, the LCD used in desktop system is designed to receive waveform analog signals, rather than digital pulse signals directly generated by PC. This is mainly because most standard graphics cards in desktop systems still convert video information from initial digital signals to analog signals, and then transmit them to the display. Although the LCD of the desktop system is designed to receive analog signals, the LCD itself can only process digital information, so after receiving the analog signals from the graphics card, the LCD needs to restore the analog signals to digital signals for processing. In order to solve the display shortage caused by the above problems, the latest desktop LCD adopts a special graphics card with digital connector, which directly transmits digital signals to the LCD display.
With the continuous maturity and development of LCD technology, the size of the display screen is gradually increasing. In the past, notebook computers used 8-inch (diagonal) fixed-size LCD monitors. Now, LCD, a desktop system based on TFT technology, can support 14 to 18 inch display panels. Generally speaking, the size of a 15-inch LCD is equivalent to that of a traditional 17-inch color display, because manufacturers decide the size of the LCD according to the size of the actual viewing area, rather than the size of the CRT.
Two. Overview of LCD technology
& lt& gtPPI and resolution
Several display manufacturers, including Toshiba, a leading LCD manufacturer, used this EDEX exhibition to release a newly developed 200PPI TFT LCD screen with real high resolution. PPI stands for pixels per square inch. Therefore, the higher the PPI value, it means that the display screen can display higher density images. Of course, the higher the display density, the higher the fidelity. At present, most common TFT LCD screens are only 100PPI, so you can imagine what effect it will have if you have twice the display quality of 200PPI.
The exposure of<& gt low temperature polysilicon display screen
In addition to the infighting among major manufacturers in the quality of displays, the display area is of course also a battleground for military strategists. TFT display screens with large display area have come out one after another. Toshiba will formally apply 15-inch low-temperature polysilicon TFT technology to display screen or notebook computer products around the autumn of 2000.
& lt& gt New resolution standard
I believe everyone is familiar with the resolution standards of VGA, SVGA and even UXGA. But have you heard of this latest resolution standard SXGA+? SXGA+ indicates that the display resolution is 1400× 1050. In fact, at the "LCD/PDP Internalization 99'" exhibition held in June of 199, three manufacturers, such as IBM, Samsung and Hitachi, have exhibited the display screens with SXGA+ resolution standard. In this EDEX 2000, Sharp exhibited 13.3-inch/14. 1 inch and 15-inch TFT display screens made with this latest notebook resolution standard.
& lt& gt Four VGA
Mitsubishi also exhibited a LCD product with the latest resolution standard. The resolution represented by "Quad-VGA" is 1280×960. Compared with the general standard XGA's display resolution of 1280× 1024, Quad-VGA will appear a little flat, with the aspect ratio exceeding 4: 3. In the future, Sony will use "Quad-VGA" standard display screen in its L series VAIO notebook computer.
Third, the noun explanation
When many people buy computer products, they are often confused by proper nouns in the explanatory materials. The same is true for choosing a liquid crystal display. There are some nouns that you haven't touched on weekdays that will make you feel at a loss. Therefore, in the next article, the author will simply sort out and explain some important technical terms related to LCD, so that everyone can have a reference when purchasing LCD.
1, size indication and viewing angle
The biggest difference between LCD display and CRT display is the different dimensions. For example, CRT monitors are advertised as 17 inches in the manual, and the actual visual size is definitely less than 17 inches, only about 15 inches; As far as LCD screen is concerned, if it is labeled as 15. 1 inch display, then the visual size is 15. 1 inch.
To sum up: the size indication of CRT display is based on the diagonal length of the shell; On the other hand, on the LCD display, only the diagonal of the visible range is used as the basis of marking.
As far as the liquid crystal displays on the market are concerned, the viewing angles are all symmetrical (that is, the angles of seeing the images on the screen from the left or right are the same). For example, the left viewing angle is 60 degrees, and the right viewing angle must be 60 degrees). The up and down viewing angles are usually smaller than the left and right viewing angles.
From the user's point of view, the bigger the viewing angle, the better. But you must understand the definition of perspective. When we say that the viewing angle is 80 degrees from left to right, it means that we can still clearly see the image on the display when we stand 80 degrees from the normal of the display (that is, the imaginary line in the middle of the display) to the left or right of the normal. Because everyone's eyesight is different, we take contrast as the standard. The greater the contrast measured at the maximum viewing angle, the better.
2. Brightness and contrast
The acceptable brightness of TFT LCD display is above 150cd/m2. At present, the brightness of TFT LCD that can be seen in the domestic market is about 200cd/m2 (the brightness measurement unit of LCD is "cd/m2", commonly known as nit). If the brightness is too low, the screen will feel darker. Of course, a little brighter would be better. However, if the screen is too bright, people's eyes will feel tired when they look at the screen for too long. So for most users, too high brightness has no practical significance.
Compared with CRT display, brightness and contrast have greater influence on the image presentation of LCD display. A high-brightness LCD screen will make users feel better. However, it is also necessary to provide high enough contrast to display brightness, so as to ensure the authenticity of color and the accuracy of color scale.
The brightness of TFT LCD displays ranges from 150 nits to 200 nits. Generally speaking, the standard brightness of a good quality LCD display should be at least 200 nits, while the maximum brightness of most CRT displays is only about 150 nits. Taking the brightness of 200 nits as an example, the image performance of LCD display is better than that of CRT display. Consumers should pay special attention to the brightness index when buying monitors, because there is no exact standard to measure whether the brightness is bright enough.
In addition, it is worth noting that the LCD screen is very bright in the central part of the screen, and the brightness near the edge will drop by nearly 25%. The best and most effective method is to compare liquid crystal displays side by side.
Contrast index refers to measuring the different brightness levels between the brightest white and the darkest black. When the contrast reaches 120: 1, vivid and rich colors can be easily displayed. When the contrast ratio is as high as 300: 1, all levels of colors can be supported.
At present, there is no effective and fair standard to measure the contrast and brightness index when users buy LCD monitors. So the best way to identify is to judge with your own eyes. Turn the LCD monitor to the brightest and darkest to see how it feels. Now we can only use this method to find a more suitable LCD.
3. Response time
The so-called "response time" is the response speed of the LCD to the input signal, that is, the response time of the LCD from dark to bright or from bright to dark.
Basically, the smaller the "response time" indicator, the better. The shorter the response time, the user will not feel ghosting or dragging when watching the moving picture. Generally, various liquid crystal displays divide the reaction speed into two parts-"rising" and "falling", and the expression is the sum of them.
4. Display color
Early color LCD displays can only display high color (256K) at most. So many manufacturers use the so-called FRC (Frame Rate Control) technology to display full-color images through simulation. Recently, due to the progress of technology, liquid crystal displays can display at least high-color 16-bit colors. In terms of resolution, taking 15. 1 inch TFT LCD as an example, it can basically support the resolution of 1024x768; Liquid crystal displays larger than 17 inch can reach the resolution of 1280x 1024, and it is easy to display colors in full-color (32-bit) mode.
5. Screen refresh frequency
For CRT display, the refresh rate is related to the speed of picture refresh. The faster the refresh rate, the less likely the picture will flicker. However, if the refresh rate is above 75Hz, users will not easily feel the screen flicker.
For liquid crystal displays, the refresh rate will not make the picture flicker. When the refresh rate is 60Hz, LCD can get a good picture. In the LCD display, each pixel continues to emit light until the non-emission signal is sent to the controller, so the LCD display will not flicker due to continuous charging and discharging.
Some people may ask: If most liquid crystal displays can achieve the best picture quality at the refresh rate of 60Hz, why not lock the refresh rate at 60Hz, but have a choice range of 60-75Hz? In fact, this is related to the flexibility and compatibility of use. Because LCD monitors try to replace CRT monitors in the market, and most graphics cards are still designed for CRT monitors, higher flexibility and compatibility will help LCD monitors cut into the market and replace CRT monitors.
Step 6 solve
Whether you buy an LCD or a general CRT monitor, resolution is the main measure of the monitor. Because the display must support the resolution required by hardware and software.
The resolution supported by traditional CRT monitors is more flexible. Both high resolution and low resolution can be displayed without any loss of display quality. This is because the image of CRT display is mainly produced by points and lines composed of pixels, so the number of pixels is an important factor affecting the resolution.
But LCD only supports the so-called "true resolution", which is comparable to the highest resolution of general CRT displays. The main difference is that LCD liquid crystal display can only present the best image effect under "true resolution". When the resolution is lower than the real resolution, the image can still be presented, but the displayed image cannot be optimized to the real resolution. The real resolution of LCD is defined as "fixed-point form", so when using LCD, we must remember to set the resolution to the highest, so that the image presented in the picture will be clearer and feel better when using it.