China Education Equipment Procurement Network News: The design and application of large-screen projection systems are complementary aspects of system engineering involving multiple subjects including projector performance, screen performance, ergonomics, optics, and civil engineering. 1. Purchase of projector First of all, it is necessary to clarify the nature of the source to be displayed That is, what is its line frequency is output by the old display card. According to the nature of the displayed source, projectors can be divided into three types: ordinary video machines, digital machines, and graphic machines. When only full TV signal is displayed, such as playing video tape in karaoke hall, you can choose a common video machine; to display the signal output by VGA, you can use a data projector with a line frequency of less than 60KHz, and choose a digital machine. You can decide which grade of projector to buy according to the actual projection content. If the software displayed is based on general teaching and word processing, the resolution is 640 × 480 (VGA); if the requirement is higher, then To select SVGA (800 × 600), such as LP260 / LP340, (1024 × 768), such as LP350, when displaying high-resolution graphics signals, you must select a digital machine with a line frequency above 60KHz. Confirm the installation method Projector installation methods are divided into table type front projection, ceiling front projection, table type rear projection, and ceiling rear projection. Front projection is where the projector's audience is on one side; rear projection is when the projector and the audience are at both ends of the projection screen. If it is used temporarily, you can choose a table-type front projection. This method is greatly affected by ambient light and the layout is messy. . For fixed use, you can choose the ceiling mode. If the space is large and there are overall arrangements during civil construction, the overall effect of choosing the rear projection method is the best. If the space is small, the method of rear projection refraction can be selected. Understand the display environment, such as room size and lighting conditions If the room area is small, LCD projector is optional. When the display environment area is large, there is no sunlight, the lighting is dim, and it is relatively fixed to use. You can choose a CRT projector. When the requirements for ambient light are not high, the display area is extremely large, and high-resolution graphics signals are displayed, the LCD light valve projector can be selected; instead of displaying high-resolution graphics signals, the pursuit of uniformity of the display screen and sharpness of colors can be DLP projector. On-site shopping tips After confirming the selected model, how to identify the actual index of the projector through the projected picture under the condition of on-site power-on? Check the horizontal scanning tracking frequency range According to the horizontal scanning frequency scanning range given in the technical indicators, select three frequencies from high, medium and low to calculate the image resolution corresponding to the three frequency points. Check whether the projector can display normally under these three resolutions. If the line is out of synchronization, that is, the screen twists or shakes, etc., it means that the horizontal scanning and tracking are poor. To check the focusing performance, use the test grid generated inside the projector, or the test grid generated by the signal generator or computer, adjust the focus to the best position, change the image contrast from low to high, and observe the horizontal and vertical lines of the grid Whether there is no defocusing phenomenon, if there is, it indicates poor focusing performance. Check the video bandwidth. Video bandwidth directly affects the details of the video. Use a computer or a signal generator to generate a white background graphic signal that the projector can reach the highest resolution, and observe whether the smallest character graphic on the screen is clear. For example, when the video bandwidth of the side camera is insufficient, the lines displayed on the screen are solid, while the vertical lines are dull, and the image details are blurred. The on-site inspection station of the LCD projector produced a completely white image to observe the color uniformity. Generally speaking, the color uniformity of LCD projectors is difficult to reach a high standard. But the timing uniformity of the good quality machine is relatively better. In addition, the dustproofness of the LCD projector is a problem. A small amount of dust, such as falling on the LCD panel or lens, may be amplified very clearly. On the all-white image, adjust the optical focus from small to large. Observe that if colored spots appear on the screen, there may be dust on the LCD panel or lens. It is estimated that the machine's dustproof system is defective. 2. Purchase of screen Choosing the right screen according to the actual use can meet your needs and get the best projection effect. The following instructions provide guidance for you to choose the most suitable screen. Although these instructions will be applicable in most cases, there are no strict rules for each introduction, depending on your actual use environment. There are four main steps to properly select the projector screen: Choose the screen type: The type you choose should be the most suitable for your specific use needs. For example: the front projection screen needs to choose the type of wall hanging or ceiling mounting, and there are manual and electric specifications; the rear projection screen needs to choose the hard screen or soft screen. In general, if you need a fixed-location projection venue, then a wall-mounted, ceiling-mounted or tripod-type screen is your best choice. If you need to move the screen to a different orientation, a portable screen is your best choice. Choose the best screen size: To choose the best screen size mainly depends on the area of ​​the space used to plan the number of seats and the location of the audience. The first rule is to choose a screen suitable for the audience-not a screen suitable for the projector, that is to put the audience's visual experience first. We provide the following formula for selecting the screen size for your reference: The screen height is approximately equal to 1/6 of the distance from the screen to the last row of seats in the auditorium, so that the audience in each row can clearly see the content of the projection . * The distance between the screen and the first row of seats should be greater than 2 times the height of the screen. * The bottom of the screen should be at least about 122 cm away from the seat of the auditorium. The choice of projector screen fabric: the screen fabric you choose should suit the needs of your projector and audience. However, if a screen needs to be used by multiple projectors, the screen fabric should be selected to suit the needs of the projector with higher screen requirements. For example, when you have both a slide projector and an image projector, because the light output of the projector is lower than that of the slide projector, you should choose the fabric whose reflectance parameter is suitable for the projector. However, because the brightness of most projectors is relatively high, the use of white plastic screens with lower reflectance than glass bead screens can achieve better projection effects.
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