At present, there are three kinds of projection technology: CRT, LCD, and DLP.
CRT projector is the earliest projection technology, which is similar to the CRT display. It has the advantages of long life, rich color display, good reducibility, and rich ability to adjust geometric distortion. Due to technical constraints, it is impossible to improve the resolution and lumen at the same time. Therefore, CRT projectors have been phased out at this stage.
The technology of LCD projector is transmission projection technology, which is the most mature at present. The color of the projection screen is restored to be true and bright. With high color saturation and high light utilization efficiency, an LCD projector has a higher brightness output. At present, the LCD projector is the main projector with a high lumen in the market. Its disadvantage is that the black layer is not very good. LCD projection technology is divided into LCD and 3LCD. The difference between them lies in the color restoration degree and picture quality.
DLP reflective projection technology. The gray level and signal-noise ratio of DLP projector image are greatly improved, and the image quality is fine and stable. In particular, when playing dynamic video, the image is more smooth, without pixel structure sense, the image is natural, and the digital image restoration is true and accurate. The advantage of DLP compared with 3lcd is that there is no crosstalk between grayscale and 3D.
Of course, there is also LCOS projection technology, which is a new projection technology. Because the cost is too high, it is seldom used
Contrast is the ratio of black to white, that is, the gradient level from black to white. The larger the ratio, the more gradients from black to white, and the richer the color representation. Contrast is very important to the visual effect. Generally speaking, the larger the contrast is the clearer the image is, and the brighter the color is. However, if the contrast is small, the whole picture will be gray. High contrast is very helpful for the clarity, detail, and gray level of the image. High contrast has advantages in black-and-white contrast, clarity, integrity, and so on. Relatively speaking, in the aspect of the color level, the influence of high contrast on an image is not obvious. The contrast has a greater impact on the dynamic video display effect. Because of the fast conversion of light and dark in the dynamic image, the higher the contrast, the easier it is for the human eyes to distinguish such a conversion process. The products with high contrast have more obvious advantages in detail performance, clarity, and high-speed moving objects performance in some dark scenes.
The brightness of the projector is usually expressed by light out, which describes the ability of light source radiation to produce a visual response in unit time, and its unit is the lumen. There are two methods to measure brightness. 1. The average brightness of 9 intersections of "Tian" is multiplied by the length and width of projection. Test precondition projection distance is 2.4m; the projection size is 60 inches. 2. All black and all white contrast method. Select a black-and-white contrast image, measure, and calculate the black-and-white brightness difference times the projected area. When choosing the projector to determine the brightness index, we should not only consider the size of the used space but also consider the influence of the use of environment brightness. And the brightness selection should leave a margin, and the brightness will decrease after a period of use due to the influence of the bulb. It is recommended to choose 800-2000 lumens for the brightness of the home projector, 2000-4500 lumens for a small conference room or standard classroom, 3500-5000 lumens for medium conference room, and ladder classroom, and 5000 lumens for large conference room or auditorium. Of course, this is only a reference value. The accurate brightness should be calculated according to the actual ambient brightness and the size of the screen. For example, taking the classroom as an example, the average brightness is 500lux, and the formula is projector brightness = ambient brightness * 2 (Times) × screen length * screen width * 1.2 (loss coefficient) ≈ 3300. Therefore, it is necessary to fully consider the use environment and cost performance to select the appropriate brightness index.
Zoom ratio: the ratio of the maximum focal length to the minimum focal length, that is, the zoom ratio of the projection picture under a certain projection distance. This parameter does not affect the projection distance, etc.
Projection ratio: projection distance / screen width.
Lens focal length: distance from LCD panel to lens, unit: mm
Projection distance: distance from lens to screen, unit: mm
Panel size: LCD size in inches
Screen width: the effective width of the screen, in inches. It should be noted that the aspect ratio should be the same as that of the panel.
Calculate the projection distance according to the projector: projection distance = screen width * lens focal length/panel size
Projection distance = screen width (mm) × projection ratio
Calculate the appropriate projector according to the site conditions: lens focal length = projection distance * panel size/screen width
Precautions for projector installation:
1. Accurately calculate the projection distance, which is the distance between the lens and the screen; align the projector lens with the left and right center of the screen as much as possible; calculate the installation height of the projector according to the difference between the lens and the screen height (refer to the projector manual). Special attention shall be paid to this item when using a fixed focus projector, so as to avoid that the image cannot be full screen or over the screen. In case of slight error, fine adjustment can be made through the relative position between the projector and hanger.
2. During construction, pay attention to load-bearing reinforcement for the installation position of the projector and curtain according to the actual situation on site.
3. Try to select the projector hanger with excellent quality. The poor hanger is not perpendicular to the roof, and the installation screws cannot be tightened. Such problems affect construction efficiency.
4. If the electric screen is selected, a strong electric socket shall be reserved in the screen box, and the electric screen shall be equipped with remote control as far as possible to avoid affecting the appearance.
5. Do not power off the projector immediately after debugging. After the bulb cools and the fan stops rotating, cut off the power.
6. For projector cable, VGA, HDMI, and other cables can be reserved according to specific requirements, and network cable can be reserved according to specific functions of the projector.