Refers to the light energy output by the projector, the unit is “lumens” (lm). A physical quantity related to light output is brightness, which refers to the ratio of the light energy emitted by the surface of the screen to the area of the screen. The common unit of brightness is “lux” (lx, 1lx=1lm/m2). When the light output by the projector passes a certain amount, the larger the projected area, the lower the brightness, and vice versa, the higher the brightness. The factors that determine the light output of the projector are the projection and phosphor screen area, performance and lens performance. Generally, the phosphor screen area is large and the light output is large. The performance of the projector lens with the liquid coupling lens is good, and the light output of the projector can be improved accordingly.
Horizontal scanning frequency
The movement of electrons from left to right on the screen is called horizontal scanning, or line scanning. The number of scans per second is called the horizontal scan frequency. The horizontal scan frequency of the video projector is fixed, 15.625KHz (PAL system) or 15.725KHz (NTSC system). The scanning frequency of data and graphic projectors is not a different frequency band; In this frequency band, the projector can automatically track the horizontal frequency of the input signal, and the phase-lock circuit realizes complete synchronization with the horizontal frequency of the input signal. The horizontal scanning frequency is an important projector index that distinguishes the grade of the projector. A projector with a frequency range of 15kHz-60kHz is usually called a data projector. The upper limit frequency exceeds 60kHz is usually called a graphic projector.
Vertical scan frequency
The electron beam moves from top to bottom while scanning horizontally. This process is called vertical scanning. Each scan forms an image. The number of scans per second is called the vertical scan frequency, and the vertical scan frequency is also called the refresh frequency, which represents the number of times the image is refreshed per second. The vertical scanning frequency is generally not less than 50Hz, otherwise the image will have a sense of flicker.
The total bandwidth of the video channel of the projector is defined as the upper limit frequency of the corresponding signal when the video signal amplitude drops to 0.707 times. The increment corresponding to 0.707 times is -3db, so it is also called -3db bandwidth.
There are three resolutions: addressable resolution, RGB resolution, and video resolution.
For CRT projectors, addressable resolution refers to the high pixels that the projection tube can distinguish. It is mainly determined by the focusing performance of the projection tube and is an important parameter of the quality index of the projection tube. The addressable resolution should be higher than the RGB resolution. RGB resolution refers to the high pixels that the projector can pass through when the RGB resolution video signal is connected, such as a resolution of 1024×768, which means that the horizontal resolution is 1024, the vertical resolution is 768, the RGB resolution and the horizontal scanning frequency , Vertical scanning frequency and video bandwidth are all related. Video resolution refers to the high resolution of the projector when displaying composite video. Here, it is necessary to analyze the relationship between the video band, the horizontal scanning frequency, the vertical scanning frequency and the RGB resolution: first look at the relationship between the horizontal scanning frequency and the vertical scanning frequency. In the projector index, the resolution is a concept that is easy to confuse, and it is often given in the projector technical index
Focusing performance of CRT tube
The small units of graphics are pixels. The smaller the pixels, the higher the graphics resolution. In CRT tubes, small pixels are determined by focusing performance. The so-called addressable resolution refers to the number of small pixels. The projector focusing mechanism of CRT tube includes electrostatic focusing, magnetic focusing and electromagnetic composite focusing. Among them, electromagnetic composite focusing is more advanced. Its advantage is good focusing performance, especially defocusing under high brightness conditions, and high focusing accuracy. It can focus on sub-regions, edges, and four corners, so that every point on the screen is very clear.
Convergence means that the three colors of RGB are overlapped on the screen. For CRT projectors, convergence control is particularly important, because it has three RGB CRT tubes, which are installed in parallel on the ground bracket. If you want to achieve complete convergence of the image, Various distortions of the image must be corrected. As the position of the machine changes, the convergence must be re-adjusted. Therefore, the requirements for convergence are one of full functions, and the other is convenient and fast. Convergence has static convergence and dynamic convergence. Dynamic convergence has functions such as tilt, bow, amplitude, linear, trapezoid, and pincushion. Each function can be adjusted in both horizontal and vertical directions. In addition, non-linear balance, trapezoidal balance, and pincushion balance can also be adjusted. Some projectors have a point convergence function, which divides the full screen into 208 points, and adjusts the 208 points point by point, so every point on the screen is accurately converged.