投影幕种类繁多，选择难，而每种投影幕又各有特点，针对不同的应用，怎样才能发挥到最好的效果？想要为设备选对投影幕，您需要了解以下几点：
Where’s the projector: front or rear?
投影机的位置：是在前方还是背后？
Front projection means the projector and the audience are on the same side of the screen, whereas with rear projection, the projector is placed behind the screen and the audience is looking towards the projector with the screen functioning as a diffuser. Both systems have advantages and disadvantages:
正投顾名思义，指投影机和观众分布在投影幕的同侧；而背投的投影机则在投影幕的后方，观众面对投影机观看投影幕，投影幕是作为介质分散其投射光。两种投影各有优点，同时也存在缺点：
Front Projection
正投
Smaller projectors can be used compared to a rear projection.
高增益投影，视角广阔，衰减少，无损清晰度。
Projector beam must be a clear “throw” towards the screen, so presenters can cause unwanted shadows on the screen.
投影光束必须清晰地“抛”到投影幕上，避免照射到主持人，在投影幕上造成不必要的阴影。
Audience area has to be darkened to get the best result.
观众区要比较暗才可以有更好的播放效果。
White surface can be disturbing for the audience.
白色面会让观众不舒服。
Rear Projection
背投
Better contrast thanks to a wider colour palette of screen surfaces.
更多颜色可以选择，所以对比度较高。
No unwanted shadows from the presenters or actors.
可以避免主持或者表演者造成的不必要阴影。
The area behind the screen can be darkened, audience area can maintain ambient light. (ideal for taking notes during conferences)
投影幕后方区域变暗，观众区域仍可保持灯光（适合开会时做笔记）。
Darker screens can “disappear” and blend in with the set.
较深颜色的投影幕可以“消失”或与背景融为一体。
Stunning effects in combination with a digital print on the surface.
在投影幕上进行数字印刷，会有令人惊喜的效果。
Some rear projection screens can cause a “hot spot” and therefore narrow down the viewing angle.
有些背投屏幕可能会有“热点”出现，视角变窄。
The area behind the screen requires valuable space and can not be used for any other purpose.
投影幕后面的区域要有足够的空间，而且不可用作其他用途。
Dual or Twin Projection
双面投影
Some screens are used for both front and rear projection, they are called dual screens.
有些投影幕既可以正投又可以背投，所以叫做双投影投影幕。
Viewing angle: wide or narrow?
视角：宽还是窄？
The amount of light reflected by the screen is known as ‘gain’. This represents the light reflected from the screen compared to that reflected from a defined standard white reference material. Therefore, a screen with a 1.0 gain will reflect the same amount of light as the reference material. A screen rated 1.5 gain will reflect 50% more light as the reference material.
投影幕反射的光量叫做“增益”。增益是指投影屏幕表面反射的光亮度与在标准白色参考材料上相比得出的值。所以说，1.0增益投影幕反射的光与参考材料反射的光一样。而1.5增益值的投影幕反射的光比参考材料反射的光则多50%。
Gain is measured from the point of view where the screen is at its brightest, which is directly in front and at a 0° axis to the screen. Depending on the choice of screen surface, the more you move to the side and view the screen from an angle, the less bright the projected image becomes:
增益值是在投影幕最光亮时度量计算的数值，最亮的定义是指在投影幕正前方0度轴的位置。当然跟所选的屏幕面也有关系，越在屏幕两侧的角度观看，投影图象就会越暗：
A screen with a flat gain ratio diffuses light more evenly in all directions, great for seating to be placed in a wide viewing angle relative to the screen. Spectators will experience a similar image quality regardless of the angle of view.
平稳增益的投影幕光线可以均匀分布在各个方向，适合比较广阔的观赏角度。无论哪个角度的观众都可以欣赏到一样品质的画面。
A screen with a peak gain ratio is more suitable for setups with a more narrow viewing angle, as the image quality increases to those seated in the center, but drops for those seated at the outside.
峰值增益的投影幕对于坐在中心的观众比较有利，坐在外围的观众所看到的画面品质会下降。比较适合窄视角设置的观赏。
The number of projectors: single or multiple?
投影机数量：单个还是多个？
Single projectors are used in more classical setups such as, cinema’s (temporary or permanent), relay screens (e.g. on both sides of a stage) or smaller conferences (e.g. meeting rooms)
单个投影机较多用在比较传统的地方，如影院（临时或永久）、接力幕（如：舞台两侧）或者小型会议（如：会议室）。
The brightness of the projection can be increased by using a “double stack”, this is when two projectors are placed on top of each other to create one brighter image.
投影的亮度可以用“叠层”来增加，两个投影机上下叠放就可以投影出较亮的画面。
Soft edge blending is a method whereby two or more projectors are used together. The edges of each of the projected images are overlapping, creating a wider display more suitable for showing wide screen content. Obviously, this works best with screens that have a flat gain ratio and therefore reducing the “hot spot” effect and enlarge the viewing area.
边缘融合，即两个或两个以上的投影机一起使用的投影方法。每个投影图象的边缘进行重叠，创建更适合宽屏内容展示的荧幕。显然，最适合选用平稳增益比的投影幕，减弱“热点”，扩大可视范围。
Ambient lighting: relevant or not?
环境灯光：有关还是无关？
The quality of the projected image is subject to the level of ambient lighting. Generally speaking, rear projection screens are more resistant to ambient lighting than front projection screens because the latter reflects all light sources, both from the projector as ambient light.
投影画面的品质还取决于周围环境的灯光。一般来所，相对于正投幕来说，背投幕受周围灯光的影响较小，因为正投幕反射所有的光源，包括投影机和周围灯光。
A darker rear screen reflects less light, decreasing the brightness of the projected image but also of the ambient light. In theory, these screens don’t have the most spectacular test results, but in practice, they seem to give a much better result.
较暗的背投幕反射较少的光，降低了投影画面和周围灯光的亮度。理论上，两种投影幕都不会有好的测试结果，但实际上却并非如此。
High gain screens are more vulnerable to ambient light, as the amount of reflected light increases by the amount of gain.
高增益投影幕不适合周围有灯光，因为增益值高，反射的光也会增加。
Contrast ratio: important for content?
对比度：对投影内容重要吗？
Contrast is the difference between the whitest white and the darkest black displayed; the greater the contrast, the better the screen. However, ambient lighting has a big effect on screen contrast.
对比度指的是画面明暗区域最亮的白和最暗的黑之间不同亮度层级的测量，对比度越大，投影幕越好。然而，环境光对投影幕有很大的影响。
As front screens reflect all light sources, their perceived contrast is highly dependent on the presence of ambient light. Overall, front projection screens with higher gains will do the best job of preserving image contrast.
因为所有正投幕反射所有的光源，所以它的对比度很大程度上取决于周围的灯光。总体来说，高增益的正投幕在保持图像对比度方面取得很大的成功。
Since a projector cannot project black in its content, it is actually the absence of light that you are seeing. Darker screen surfaces reflect less of the ambient light sources and they appear to have “darker” black levels because of the colour of the projection surface. This actually increases the contrast perception of the projected image.
由于投影机无法投射黑色内容，所以看到的黑色其实就是没有光线。较暗的投影幕反射较少的光源，由于投影面本身颜色较深，因此看上去的黑色“更暗”。这在实际使用中反而增加了投影画面的对比度。
