投影幕種類繁多，選擇難，而每種投影幕又各有特點，針對不同的應用，怎樣才能發揮到最好的效果？想要為設備選對投影幕，您需要了解以下幾點：
Where’s the projector: front or rear?
投影機的位置：是在前方還是背后？
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:
正投顧名思義，指投影機和觀眾分布在投影幕的同側；而背投的投影機則在投影幕的后方，觀眾面對投影機觀看投影幕，投影幕是作為介質分散其投射光。兩種投影各有優點，同時也存在缺點：
Front Projection
正投
Smaller projectors can be used compared to a rear projection.
高增益投影，視角廣闊，衰減少，無損清晰度。
Projector beam must be a clear “throw” towards the screen, so presenters can cause unwanted shadows on the screen.
投影光束必須清晰地“拋”到投影幕上，避免照射到主持人，在投影幕上造成不必要的陰影。
Audience area has to be darkened to get the best result.
觀眾區要比較暗才可以有更好的播放效果。
White surface can be disturbing for the audience.
白色面會讓觀眾不舒服。
Rear Projection
背投
Better contrast thanks to a wider colour palette of screen surfaces.
更多顏色可以選擇，所以對比度較高。
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陰影。
The area behind the screen can be darkened, audience area can maintain ambient light. (ideal for taking notes during conferences)
投影幕后方區域變暗，觀眾區域仍可保持燈光（適合開會時做筆記）。
Darker screens can “disappear” and blend in with the set.
較深顏色的投影幕可以“消失”或與背景融為一體。
Stunning effects in combination with a digital print on the surface.
在投影幕上進行數字印刷，會有令人驚喜的效果。
Some rear projection screens can cause a “hot spot” and therefore narrow down the viewing angle.
有些背投屏幕可能會有“熱點”出現，視角變窄。
The area behind the screen requires valuable space and can not be used for any other purpose.
投影幕后面的區域要有足夠的空間，而且不可用作其他用途。
Dual or Twin Projection
雙面投影
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，所以叫做雙投影投影幕。
Viewing angle: wide or narrow?
視角：寬還是窄？
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與在標準白色參考材料上相比得出的值。所以說，1.0增益投影幕反射的光與參考材料反射的光一樣。而1.5增益值的投影幕反射的光比參考材料反射的光則多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時度量計算的數值，最亮的定義是指在投影幕正前方0度軸的位置。當然跟所選的屏幕面也有關系，越在屏幕兩側的角度觀看，投影圖象就會越暗：
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.
平穩增益的投影幕光線可以均勻分布在各個方向，適合比較廣闊的觀賞角度。無論哪個角度的觀眾都可以欣賞到一樣品質的畫面。
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.
峰值增益的投影幕對于坐在中心的觀眾比較有利，坐在外圍的觀眾所看到的畫面品質會下降。比較適合窄視角設置的觀賞。
The number of projectors: single or multiple?
投影機數量：單個還是多個？
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)
單個投影機較多用在比較傳統的地方，如影院（臨時或永久）、接力幕（如：舞臺兩側）或者小型會議（如：會議室）。
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“疊層”來增加，兩個投影機上下疊放就可以投影出較亮的畫面。
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.
邊緣融合，即兩個或兩個以上的投影機一起使用的投影方法。每個投影圖象的邊緣進行重疊，創建更適合寬屏內容展示的熒幕。顯然，最適合選用平穩增益比的投影幕，減弱“熱點”，擴大可視范圍。
Ambient lighting: relevant or not?
環境燈光：有關還是無關？
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.
投影畫面的品質還取決于周圍環境的燈光。一般來所，相對于正投幕來說，背投幕受周圍燈光的影響較小，因為正投幕反射所有的光源，包括投影機和周圍燈光。
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.
較暗的背投幕反射較少的光，降低了投影畫面和周圍燈光的亮度。理論上，兩種投影幕都不會有好的測試結果，但實際上卻并非如此。
High gain screens are more vulnerable to ambient light, as the amount of reflected light increases by the amount of gain.
高增益投影幕不適合周圍有燈光，因為增益值高，反射的光也會增加。
Contrast ratio: important for content?
對比度：對投影內容重要嗎？
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.
對比度指的是畫面明暗區域最亮的白和最暗的黑之間不同亮度層級的測量，對比度越大，投影幕越好。然而，環境光對投影幕有很大的影響。
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.
因為所有正投幕反射所有的光源，所以它的對比度很大程度上取決于周圍的燈光。總體來說，高增益的正投幕在保持圖像對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.
由于投影機無法投射黑色內容，所以看到的黑色其實就是沒有光線。較暗的投影幕反射較少的光源，由于投影面本身顏色較深，因此看上去的黑色“更暗”。這在實際使用中反而增加了投影畫面的對比度。
