Detailed explanation of performance index of projector
The performance index of projector is a mark to distinguish the grade of projector, mainly including the following indexes: < br / >
Optical output < br / >
It refers to the light energy output by the projector, and the unit is "lumen". A physical quantity related to light output is brightness, which refers to the ratio of the light energy emitted by the light on the screen surface to the screen area. The commonly used unit of brightness is "lux" (LX, 1LX = 1lm / m2). When the light output by the projector passes through a certain area, the larger the projection area, the lower the brightness, otherwise, the higher the brightness. The factors that determine the light output of projector include the area of projection and fluorescent screen, performance and lens performance. Usually, the area of fluorescent screen is large and the light output is large. The performance of projector lens with liquid coupling lens is good, and the light output of projector can be improved accordingly.
Horizontal scanning frequency < br / >
The movement of electrons from left to right on the screen is called horizontal scanning, or line scanning. The scanning frequency per second is called horizontal scanning frequency. The horizontal scanning frequency of video projector is fixed. The scanning frequency of 15.625kHz (PAL system) or 15.725khz (NTSC system) data and graphic projector is not different frequency band. In this frequency band, the projector can automatically track the input signal line frequency, and the phase-locked circuit can realize the complete synchronization with the input signal line frequency. Horizontal scanning frequency is an important index to distinguish the grade of projector. A projector with a frequency range of 15khz-60khz is usually called a data projector. Those whose upper frequency is more than 60 kHz are usually called graphic projectors.
Vertical scanning frequency < br / >
When the electron beam is scanning horizontally, it moves from top to bottom. This process is called vertical scanning. Each scan forms an image. The number of scans per second is called the vertical scan frequency. The vertical scan frequency is also called the refresh frequency. It represents the number of times the image is refreshed per second. The vertical scanning frequency is generally no less than 50Hz, otherwise the image will have a flicker sense.
Video bandwidth < br / >
The total band width of the video channel of the projector is defined as the upper limit frequency of the corresponding signal when the amplitude of the video signal drops to 0.707 times. The increment of 0.707 times is - 3dB, so it is also called - 3dB bandwidth.
Resolution < br / >
There are three resolutions: addressable resolution, RGB resolution and video resolution.
For CRT projector, the addressable resolution is the highest resolution pixel of the projection tube, which 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 highest pixel that the projector can pass when receiving RGB resolution video signal. For example, the resolution is 1024 & times; 768, which means the horizontal resolution is 1024, and the vertical resolution is 768. RGB resolution is related to the horizontal scanning frequency, vertical scanning frequency and video bandwidth.
Video resolution refers to the highest resolution of the projector when displaying composite video. Here, it is necessary to analyze the relationship between video band, horizontal scanning frequency, vertical scanning frequency and RGB resolution: first, look at the relationship between horizontal scanning frequency and vertical scanning frequency.
Focusing performance of CRT tube < br / >
The smallest unit of a graph is the pixel. The smaller the pixel, the higher the graphics resolution. In CRT, the minimum pixel is determined by the focusing performance. The so-called addressable resolution refers to the number of minimum pixels. There are three focusing mechanisms of CRT projector: electrostatic focusing, magnetic focusing and electromagnetic compound focusing. Among them, electromagnetic compound focusing is more advanced, which has the advantages of good focusing performance, especially defocusing under high brightness conditions, and high focusing accuracy. It can focus in different regions, edges and corners, so that every point on the screen is very clear.
Convergence refers to the coincidence of three RGB colors on the screen. For CRT projector, convergence control is particularly important, because it has three RGB CRT tubes, which are installed in parallel on the ground bracket. In order to achieve complete convergence of images, all kinds of distortion of images must be corrected. The change of machine position and convergence also need to be readjusted. Therefore, the requirements for convergence are full function and convenience. There are static convergence and dynamic convergence, and dynamic convergence has tilt, bow, amplitude, linear, trapezoid, pillow and other functions. Each function can be adjusted in horizontal and vertical directions. In addition, it can adjust the nonlinear balance, trapezoid balance and pillow balance. Some projectors have the function of point convergence, which divides the whole screen into 208 points and adjusts them point by point on 208 points, so every point on the screen can achieve accurate convergence.