[Shopping school: seven criteria for choosing front projection screens] Projection screens
When users are faced with screen selection, they may have a lot of doubts. Da-Lite provides seven screen selection criteria for different application environments.
1. Video projector type
CRT technology: CRT projector is what we usually call a three-shot projector, composed of three projection tubes, CRT projector decomposes the input signal source into R (red), G (green), B (blue) ) On the phosphor screen of the three CRT tubes, the luminous signals are amplified, converged and displayed on the large screen under high pressure. This type of projector has the characteristics of rich image color and high resolution, but its disadvantage is that the brightness is usually low. .
LCD technology: LCD technology uses traditional light sources, usually metal halide lamps. The three primary colors of red, green, and blue are completed by three separate liquid crystal panels, and the three primary colors can almost reach the screen for imaging at the same time.
DLP technology: The full English name of DLP is Digital Light Processor, which means 'digital light processor'. This technology is a patented technology developed by Texas Instruments. It is a projection technology using DMD (Digital Micormirror Device) as the imaging device. A digital micro-reflector is used as a light valve imaging device. Even a single-chip DMD is composed of many micro-mirrors. The physical resolution of the DLP projector is also determined by the number of micro-mirrors. Many small micromirrors together form a DMD, and each micromirror reflection image represents a pixel.
D-ILA technology: D-ILA is a direct drive image light source amplifier technology. The core component of its technology is a reflective active matrix liquid crystal on silicon panel, which is commonly referred to as a reflective liquid crystal panel (LCOS), so the industry refers to this technology as reflective liquid crystal technology. The advantage of this technology is that the brightness and contrast are relatively high.
LCOS technology: This projection technology uses a CMOS integrated circuit chip coated with liquid crystal silicon as the substrate of a reflective LCD. It is polished by an advanced process and then plated with aluminum as a mirror to form a CMOS substrate, and then the CMOS substrate It is laminated with the glass substrate containing the transparent electrode, and then is packaged by injecting liquid crystal. LCOS places the control circuit behind the display device, which can increase the light transmittance, thereby achieving greater light output and higher resolution.
35mm slide projector: This technology is one of the most common projection methods when displaying a single image. Like other portable film projection methods, slides can be played continuously, and the output brightness of the projector is also very high (from 1000-6000 lumens), which can project very perfect picture details, and the colors are also very rich.
In business and education applications, overhead projectors are also a common projection method. They are flexible to install, easy to use, and have a brightness output of up to 3000 lumens. Speakers can use them according to their hobbies.
Three-dimensional projection technology is realized by using light polarization. Stereoscopic projection has high requirements on the polarization of the screen and also has high requirements on the gain of the screen. Some front projection screens will also affect the polarization effect. In some special video projection application environments, relatively high contrast is required due to the influence of ambient light, so it is best to use curved projection screens in such applications.
2. Ambient light
Ambient light is one of the key links in the projection application. After we have selected the projector, we must clarify whether the ambient light can be ideally controlled in the projection environment. Only when the light is controlled can the projection room be guaranteed. The light can be adjusted at any time as required, and the ambient light can be increased or decreased at an appropriate time, so that the projected image will not be affected by uncontrollable changes in the light. Some rooms will have some uncontrollable light, then we must determine whether the light will directly hit the screen and affect the projected image. In short, the user must have a clear understanding of all the light in the projection environment to ensure The entire projection effect is under control.
Three, display device brightness
Use the following formula to calculate the brightness of the display device
Fourth, the room setting/size
First determine whether the shape of the two sides of the audience seat and the screen is narrow and long trapezoidal (Figure 1) or rectangular (Figure 2, the viewing angle between the two sides of the seat and the center of the screen is greater than 30 degrees), if the shape of the room is set to Figure 2 If the viewing angle between the audience and the projection screen is greater than 30 degrees, you need to choose a wide viewing angle screen material.
5. Projected image requirements
Traditional video images, this type of image usually does not require very strict details, and resolution is not the most important factor.
Continuous tone image: This is the most common of various slide film projection methods, and provides the best image quality in terms of clarity and color reproduction.
Digital or pixelated data with fine details (that is, texture information used in LCD and DLP video projection equipment), in order to project high-definition image characters, higher resolution requirements are required.
6. The position of the horizontal line between the projector and the center of the screen
When the projector and the audience are on opposite sides of the central horizontal line of the screen, the screen gain is required to be higher, and a reflective screen should be used (Figure 1). When the position of the projector and the audience is in the same direction as the central horizontal line of the screen ( As shown in Figure 2), the gain requirement is higher, and retroreflective screen is recommended.
Seven, screen maintenance
See if the following situation occurs on the screen: it may be dirty or damaged due to unintentional or frequent operations. Typical situations are as follows: In places with heavy traffic, people may accidentally touch the screen surface; in public places or educational environments, it is impossible for users to protect the screen at all times; in places with suspended particles or dust problems, the screen It may be soiled.