Today, projectors have become a must-have product in daily life, not only in schools, government, etc., but even ordinary individual users have begun to use projection products. In a projection system, the projection screen or the projection screen is also part of the entire projector optical system. It not only can present the projected image, but also has a greater impact on the image display effect.
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However, in the actual process, many of them know little about the projection screen, and the importance of the projection screen is often overlooked during the projection process. During the projection process, a good projection screen can enhance the projection effect by nearly 20%, especially in digital cinema projections. In order to present high-quality movie images, it depends on three major factors, including projector level and suitability. The projection environment and projection screen quality, and whether the projection screen is suitable for the matching projection product will better enhance the projection level of the image.
Type of projection screen
First, let's first introduce the type of projection screen. Generally speaking, the projection screen can be divided into two types: front projection and rear projection. The front projection screen can be divided into soft screen and hard screen. The soft screen has various types such as white screen, pearl screen and metal screen. The hard screen has two types of flat screen and curved screen. The rear projection screen can also be used. It is divided into a soft screen and a hard screen.
Front projection screen
In the front projection screen, we can usually see the manual hanging curtain, electric hanging curtain, two-legged bracket curtain, triangular branch
There are many types of curtains and hanging screens. Among them, the manual hanging screen, the two-legged bracket screen and the triangular bracket screen can be used in one scene, which can be applied to different places, such as various types of mobile digital film screening; while the electric hanging screen and the hanging screen are suitable for conference rooms and theaters. Such as fixed places.
Rear projection screen
The rear projection screen can be divided into a hard rear projection screen and a soft rear projection screen. Generally speaking, the hard rear projection screen has better picture quality than the soft rear projection screen, so it is said that during the actual projection application process. The application of the rear projection hard screen is still more.
Projection screen type
Soft screen
In general, soft screens can be divided into white screens and beaded screens depending on the manufacturing process and surface coating.
First, a white matt screen is introduced. This projection screen is similar to a white canvas. It is painted on a special fabric and is made after a simple treatment. More importantly, the surface of the screen is rough, its effect on image sharpness is minimal, the brightness of the projected image is uniform, and there is no directionality, and it has low price, wide viewing angle, soft visual effect, etc. advantage.
However, the shortcoming of this white matte curtain is that the brightness gain is not high, and it has high requirements for the light-shielding effect of the projection environment during the projection process. Therefore, it is more suitable for use in small and medium-sized conference rooms, and it will work better with high-brightness projectors.
In addition to the second glass bead curtain, this screen is uniformly coated with fine glass beads on the surface of the curtain base, and this fine glass bead can play a role of concentrating light, so the screen has a certain directionality. And its incident light will basically reflect in the original direction, and the gain of light will be quite high.
Moreover, the screen is moderately priced, has a wide viewing angle, is resistant to aging, is not easy to fade, and has good color reproduction. The disadvantage is that it is not suitable to roll up repeatedly, because in this case, the glass beads will easily fall off, which will affect its future use.
However, this glass bead curtain has the characteristics of strong directivity and high optical gain, which also makes it more adaptable. In a projection classroom that is highly demanding on brightness, it is a better choice to equip such a screen.
At present, in the domestic market, there are two kinds of soft screens: domestic and imported. The imported screen is characterized by good quality. The general use period is 2 years, but the price is relatively expensive. The domestic soft screen is relatively cheap, and the specifications are complete. , after-sales service is also done better, but generally after a year of use will gradually turn yellow and curling.
Hard screen
The hard screen is generally made of metal, which can be divided into aluminum foil reflective screen and silver powder screen. The surface of the curtain surface of the aluminum foil reflective curtain is usually coated with a layer of aluminum foil, and the aluminum foil is used to reflect the projection light; the silver powder screen is evenly coated with silver powder on the curtain base to reflect the projected light.
The advantage of these metal screens is that the reflection coefficient is high, and the brightness of the reflected light is larger than that of the white matte screen. When used in conjunction with a low-brightness projector, it can enhance the visual effect; and the disadvantage is that it is expensive and exists. The problem of viewing angle, which is made of metal, is cumbersome and easily oxidized. Therefore, it is not suitable for use with home and professional-grade projections, and can play a more important role in the field of business projection.
Introduction to projection screen technical indicators
After introducing the type and type of projection screen, I feel that it is necessary to further introduce the main technical indicators of the projection screen.
Gain
In the case where the projection light angle is constant and the projection luminous flux is constant, the ratio of the brightness of the projection screen in a certain direction to the brightness under the ideal state is called the luminance coefficient in the direction. The maximum value is referred to as the gain of the projection screen. It reflects the ability of the projection screen to reflect the projected light. It is a parameter that measures the relative value of the screen brightness and the optical properties of different screen materials.
We usually set the gain of the matt white wall to 1. If the projection screen gain is less than 1, it will weaken the projected light. If the projection screen gain is greater than 1. It will reflect or refract more of the projected light.
When introducing the gain indicator, you have to talk about the half gain and the half gain angle. In the projection screen industry, we generally define a definition of the screen brightness performance when the viewer views the image from a large angle as a half gain, and the half gain angle of the projection screen will directly affect the display effect of the screen.
The peak brightness of the projection screen refers to the value obtained when the viewer is directly in front of the screen and viewing the screen perpendicular to the center of the screen, also referred to as the 0 degree observation axis peak gain. When the viewer moves from the center of the screen to the periphery, the brightness of the projected image will decrease significantly. When the brightness falls to half of the peak brightness, the resulting screen gain is half gain. This angle is the half gain angle of the screen. The half gain angle is more Large. The content of the screen can be clearly seen by more people from different angles. It is important to choose the gain and half gain angle of the screen depending on the environment in which it is used.
Perspective
We know that the projection screen has different reflections in all directions. The farther away from the center of the screen, the lower the brightness. When the brightness is reduced to 50%, we define it as the angle of view.
When viewing an image within a viewing angle, the brightness of the displayed image must be satisfactory; while viewing the projection outside of the viewing angle, the projected brightness will be insufficient. Generally speaking, the larger the gain of the screen, the smaller the angle of view; the smaller the gain, the larger the angle of view, and the latter is the characteristic of the white screen. Therefore, in the case of a large number of occasions, we can use a white plastic screen with a small gain value, which can expand the viewing angle.
Width to height ratio
The aspect ratio of the projection screen is also an important technical indicator, which directly affects the quality of the screen. The display will only be displayed if the projection screen's aspect ratio and the projector's natural resolution and source resolution are perfectly suitable. perfect.
In the current screen market, the width and height ratio of the projection screen are as follows:
4:3, it is mainly used in video/PC image display;
16:9, mainly used in HDTV image display;
1.85:1, mainly providing support for wide-screen TV signal images;
2.35:1, mainly used in wide-screen stereo image display.
Resolution (resolution) and contrast
This technical indicator of the projection screen is mainly for the projector type. In general, the resolution of the projected image is mainly divided according to its type. Among them, the resolution parameter of the LCD/DLP/LCOS projector is measured - pixel. This refers to the value obtained by multiplying the high and wide pixels of the resolution. That is, the true resolution of the projector.
Contrast refers to the ratio of the bright and dark areas of the picture. High-contrast screens are crucial when displaying multi-screen levels.
Evenness
Finally, the uniformity of the projection screen is closely related to the projection technology. The high screen uniformity ensures that the brightness and color of the screen will be more consistent when viewing the screen at 0-180 degrees in the horizontal and vertical directions. The uniformity of the material also complements the uniformity of the projector's picture.
Projection screen basic technology
After reading the above introduction, we know that the projection screen can be divided into hard screen and soft screen in material and production process. The types of projection screens and technical parameters are related, complementary and different. The key to exploring the technology is how the material on the surface of the screen behaves, reflects and reflects the incident light. For the above two screens, there are two major projection screen technologies on the market - soft screen and hard screen technology.
Soft screen technology
Regardless of the application method, the main technology of the soft screen is to carry out various kinds on the surface of an opaque cloth.
Different materials are sprayed, and different optical materials are applied to the surface material. The optical factor and distribution in the optical material determine the gain, viewing angle and resolution of the screen. At the same time, these optical factors and other pigments optimize the color saturation and picture of the projected image.
The projection light of the rear projection is illuminated from the back to the screen and imaged. The material of the soft screen is PVC. The quality of the screen is also related to the surface material and the screen material.
Hard screen technology
The production of hard screens mainly uses optical diffuse reflection and Fresnel lens technology. The diffuse reflection screen is characterized by large viewing angle, low gain, strong adaptability to ambient light, and wide application range. One of the diffuse reflection screen technologies is to directly process the plexiglass material, the acrylic surface, the screen angle and clarity are not ideal, and the solar effect is also serious.
Another diffuse reflection screen technology is made by using a transparent material such as acrylic or glass as a substrate, and a rear-projection soft screen is attached to the surface. The screen's top, bottom, left, and right viewing angles are all 180 degrees, and there is no sun effect, and the size of such screens is generally large.
The Fresnel optical lens screen increases the gain of the screen, but its vertical viewing angle is limited. Fresnel optical lens screens vary according to the Fresnel lens slot angle, and each screen has a different focal length to meet the needs of different lens projectors.
Reasonable selection of projection screen
As the saying goes, the good horse is equipped with a good saddle. With the proper projector, we have to equip it with a suitable projection screen. Because there is no good projection screen to match, the quality of the projection will be greatly reduced.
First of all, we have to consider the projection method. So far, the projection screen technology has not reached the level of positive and negative two-way use, so in the purchase we can only choose one according to the actual situation.
When paired with the positive cast, we are more sensitive to the effects of ambient light. Therefore, when selecting the projection screen, we recommend to choose a product with higher gain under various conditions and conditions. If you need to build a high-end conference room, I recommend using a rear-projection method, which can be less affected by ambient light.
Second, we have to choose different projection screens for different projectors. For low-end LCD liquid crystal projectors, its brightness and contrast are relatively low. During projection, the projector, human eye, and screen remain parallel on the same line of sight, otherwise severe keystone distortion is likely to occur. At this time, the projection screen should select a high-gain projection screen that reflects in the direction of the incident light source. This kind of screen can compensate for the lack of brightness and the uneven brightness of the image to some extent.
High-end LCD projection and DL P projectors generally have high definition, precision imaging and progressive scanning techniques. The projected images will be clearer and more detailed, and the colors will be richer in natural and image level performance. Also quite good. When choosing the curtain, we should choose high-quality matt screen or high-grade pearl screen. The light gain of the projection screen should not be too high. Because high-gain screens produce more reflections, this can affect the projection.
Third, projector brightness and contrast should also be considered. Because the brightness of the projector directly affects the display of the screen, the brightness per unit area (L) is an important parameter to measure the effect. The calculation formula is as follows: L = B (projector brightness ANSI) / S (projection screen area). In a brighter environment, we should find ways to increase the value of L, while high gain can increase the display brightness under the same conditions. High-gain screens and low-brightness projections are very appropriate.
At present, the contrast of the projector has also been increasing. In order to improve the picture quality and better match the use of the projector, the projection screen technology is also constantly improving. The gray screen technology is to make the projection screen gray, which improves the contrast and gray level of the display screen, better reveals the details of the dark part, and makes the projection picture more colorful.
Fourth, the optical characteristics of the projector should also attract the attention of everyone. We know that the projected picture refers to both the axis and the off-axis. Optical screens have a viewing angle, while Fresnel optical screens also have a lens center, and the projection of all projectors directly affects the quality of the screen.
Users using Fresnel screens are recommended to use on-axis projectors. On-axis projectors can also choose a good quality diffuse screen. If everyone's projector is off-axis, I recommend using a front projection screen or diffuse reflection. Screen, it is best not to use Fresnel optical lens screen.
Fifth, we have to choose the right screen size. In general, the optimal screen size depends primarily on the amount of space used and the number of seats in the audience and the location. So we must first choose the screen that suits the audience, instead of simply selecting the screen that matches the projector, that is, we want to put the viewer's visual experience first. Pay attention to the following points. The height of the screen should allow the viewers of each row to clearly see the contents of the projected picture; the distance from the screen to the first row of seats should be greater than 2 times the height of the screen; The ground distance should also be around 1.5 meters.
We also need to understand the relationship between the projection distance and the brightness. The farther the distance, the lower the brightness, and the higher the gain, the higher the screen brightness. At the same time, the screen gain and viewing angle are a pair of contradictory bodies, high gain small viewing angle, large viewing angle and low gain. How can we balance the two, fish and bear's paw? We should according to the actual requirements, when the projection screen should be small size, we should consider a large viewing angle, when the projection screen is large, we should consider high gain screen.
In addition, we should also choose the format that suits the projection device used, that is, the appropriate aspect ratio, mainly between the 4:3 and 16:9 formats.
Sixth, everyone must pay attention to the lens ratio of the projector, because the lens ratio of the projector directly affects the projection distance, the relationship is: D = WX F + A. Where: D is the projection distance, F is the projector lens focal length, w is the screen image width, and A is the projector correction value.
We know that when the projection distance D and the focal length F are the same, the quality of the projected picture will be optimal. If the projector is equipped with a short-focus lens, we can achieve the desired results while saving the projection space.
Seventh, consider the use and function of the projector and screen. In general, projection screens are used in teaching, home, business, and engineering applications. The functions and parameters of the projection screen will be different for different purposes, so we have to choose the appropriate projection screen according to the specific use.
For example, in the field of teaching and business applications, we generally need larger screens to demonstrate text and other content for multi-person viewing. I recommend using a projection screen with an aspect ratio of 4:3, high resolution, and high screen gain. In the home application, the author suggests using a high contrast ratio and an aspect ratio of 16:9. At this time, the gain of the projection screen does not have to be too high; in engineering applications, we need high-resolution image images, so it should also Select a projection screen with a higher resolution.
Finally, we should also pay attention to its manufacturing process when choosing a projection screen. Of course, we don't want quality problems with the projection screens we purchase, so we should also carefully review the manufacturing process and processing quality. Some manufacturers' processes are not enough, and the installation of their screens may be troublesome. Some manufacturers may cut corners on the screen, which will make it impossible to maintain a tight and straight state after a long time of use.
The matching degree of each part of the projection screen and the indicating processing condition should also be noticed by everyone. The real high-quality screen is treated with black matte material when exposed to light, which can absorb the scattered light. This should be paid special attention.
In addition, we have to point out to everyone that in order to get better digital film screening effects, in addition to choosing a good projection screen, we should pay special attention to the improvement of the projection environment. The shading effect of the projection environment should be as good as possible. In order to prevent the projected image from becoming dull and unclear as much as possible.
Projection screen maintenance and care
Through the above introduction, we have a certain understanding of the type, type, index, and basic technology of the projection screen, and have a certain understanding of how to select the projection screen. And if you really have a projection screen, this is not everything, and you can enjoy it. We should also manage the projection screen scientifically when we use it. Such as the regular decontamination of the projection screen, when the projection screen is not used for a long time, it should also be rolled up for proper storage and so on.
Only when we do this, we will not use the projection screen to reduce the ability of the reflected light, the yellowing of the white signal, and the color distortion of the image.
The author lists the following precautions, hoping to provide a great help for the majority of consumers to use and maintain the projection screen.
1. The glass bead screen should not be folded. We can't touch the screen of the projection screen with fingers or sharp or hard objects to avoid damage.
Second, when we do the dust removal treatment on the screen surface of the special projection screen, we should use soft brush or feather duster to wipe it. If the stain is heavy, we can wipe it gently with cotton ball and clear water.
Third, if there is a stain on the bucky white plastic screen, we can wipe it gently with a damp cloth;
4. If the screen is stained with oil that is difficult to wipe, we can use the silk cloth to clean the distilled water containing the glass cleaner of Armonia (ammonia). The amount of detergent must be strictly controlled, especially for optical micro The structural curtain prevents the cleaning agent from forming a large area of ​​penetration along the lines of the rear projection screen;
Fifth, the spring reel curtain should be handled with care to avoid collision and deformation, affecting the service life of everyone;
6. In the process of using the projection screen, if there is an abnormal phenomenon, we must stop immediately and eliminate the fault in time;
7. When the voting screen is not used for a long time, we should roll in the screen, put it into the shell, and save it properly. When rewinding, we should also pay attention to check the surface of the curtain to ensure that there are no foreign objects, so that it can be rolled back;
Eight, for the electric screen, we can generally use the scrolling up and down continuously, but the time can not exceed 5 minutes, otherwise the motor will overheat and even enter the protection state automatically. When you use it again, you need to wait until the motor is cooled before you can use it;
9. When the projection screen is not in use, it should be placed in parallel in a dry place to avoid high temperature and humidity, and should be kept away from corrosive substances, and it is necessary to prevent crushing and collision between hard objects;
10. When you use the projection screen, you must not disassemble it yourself. Even if there is a problem, you should get it after the sale to avoid further damage.
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