Detailed explanation of the performance index of the projector

The performance index of the projector is a sign to distinguish the level of the projector, mainly the following indicators:

Light output
Refers to the light energy output by the projector, in units of "lumens" (lm). A physical quantity related to light output is brightness, which refers to the ratio of light energy emitted by light irradiation on the surface of the screen to the area of the screen. The commonly used unit of brightness is "lux" (lx,1lx = 1lm/m2). When the light output by the projector passes through a certain period, the larger the projection area, the lower the brightness, and vice versa, the higher the brightness. The factors that determine the light output of the projector are projection and fluorescent screen area, performance and lens performance. Usually, the fluorescent screen area is large and the light output is large. The projector lens with the liquid coupling lens has good performance, and the projector light output can be improved accordingly.

Horizontal scanning frequency
The movement of electrons on the screen from left to right is called horizontal scanning, also known as line scanning. The number of scans per second is called the horizontal scanning frequency. The horizontal scanning frequency of the video projector is fixed. The scanning frequency of the data and graphics projector is 15.625KHz(PAL system) or 15.725KHz(NTSC system). In this frequency band, the projector can automatically track the line frequency of the input signal, and the phase locking circuit can realize complete synchronization with the line frequency of the input signal. Horizontal scanning frequency is an important projector indicator to distinguish the projector grade. Projectors in the frequency range of 15kHz-60kHz are commonly referred to as data projectors. The upper limit frequency exceeding 60kHz is usually called a graphics projector.

Vertical scanning frequency
The electron beam scans horizontally while moving from top to bottom, a process called vertical scanning. Each scan to form an image, the number of scans per second is called the vertical scan frequency, the vertical scan frequency is also called 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.

Video Bandwidth
The total bandwidth of the video channel of the projector is defined as the upper limit frequency of the signal when the amplitude of the video signal drops to 0.707 times. The increment corresponding to 0.707 times is-3db, so it is also called-3db bandwidth.

Resolution
Resolution: addressable resolution, RGB resolution, video resolution three.
For CRT projectors, the addressable resolution refers to the highest pixel that can be resolved by 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 signals. For example, the resolution is 1024 × 768, which means that 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 at which the projector displays the 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.

Focusing performance
of CRT tubes The minimum unit of a graphic is a pixel. The smaller the pixels, the higher the graphics resolution. In the CRT tube, the minimum pixel is determined by the focus performance, the so-called addressable resolution, that is, the number of minimum pixels. The projector focusing mechanism of CRT tube includes electrostatic focusing, magnetic focusing and electromagnetic compound focusing. Among them, electromagnetic compound focusing is more advanced. Its advantages are good focusing performance, especially defocusing under high brightness conditions, and high focusing accuracy. It can be focused in different regions, edge focusing and four corners, thus every point on the picture can be clearly defined.

Convergence
Convergence refers to the coincidence of RGB three colors on the screen. For CRT projectors, convergence control is particularly important, because it has RGB three CRT tubes, which are installed in parallel on the support. In order to achieve complete convergence of the image, all kinds of distortions of the image must be corrected. When the position of the machine changes, the convergence must also be readjusted. Therefore, the requirements for convergence are full-featured and convenient. Convergence has static convergence and dynamic convergence, in which dynamic convergence has tilt, bow, amplitude, linear, trapezoidal, pincushion and other functions, each of which can be adjusted in both horizontal and vertical directions. In addition, can also be nonlinear balance, trapezoidal balance, pillow balance adjustment. Some projectors have a point convergence function, which divides the full screen into 208 points and adjusts them point by point at 208 points, so each point on the screen is accurately converged.