In Part 1 of this four-part series, I talked about some basic yet critical factors that will impact which projector screen you should buy, including viewing distance and screen size. In Part 2, I'll look solely at screen gain, as it is an extremely important factor, especially in today's 4K HDR world.
Every screen on the market has a "gain" rating/factor. Some screens are "negative gain" and some are "positive gain." The gain factor number represents a ratio of the light that is reflected from the screen as compared to the light reflected from a standard white (Magnesium Oxide) board. Therefore, a screen with a gain factor of 1.0 will reflect the same amount of light as that from a white board. A screen rated at 1.5 gain factor, meanwhile, will reflect 50% more light than that from a white board, whereas a gray screen with a 0.8 gain factor will reflect 80% of the light from a white board. Please note, however, that there are 1.2 gain screens that are grey in colour, too.
A screen is a passive device, so how can they have "gain?" Screens with a positive gain factor reflect more of the light incident on them toward the centre of the viewing area, producing a dimmer image the more it goes off to the sides. The higher the gain factor, the more apparent the difference in brightness between its middle area and its sides.
The most ideal home theatre screens are neutral matte white screen, i.e. have a gain factor of 1.0. Stewart's StudioTek 100 is the de-facto standard within the professional crowd, considered to be the most neutral screen for projection.
To enhance black level, some of today's screens are gray with a negative gain as low as 0.8. On the other hand, one vendor is marketing screens with gain factors that it claims to be higher than 2.0. However, unless you've gone shopping for a screen before, you're not likely to know what any of these numbers mean.
The higher the gain, however, will result in a negative side-effect of having a smaller viewing angle. With a 1.0 gain screen, you will achieve equal brightness and the most accurate colour no matter where you sit. The higher the gain factor, the smaller the viewing angle and the more chance of hot-spotting (when the middle portion of the image appears brighter than the edges when you're viewing the screen from a centre position), which can be an annoyance.
Furthermore, screens with higher gain factors tend to generate colour shifts in the image that are noticeable as the viewer moves around the screen, looking on from different angles. This anomaly happens because high gain-factor screens do not typically reflect colours equally. So once again, the image looks different to each viewer depending on where they are seated.
If you are still using a regular HD projector, I strongly recommend screen gain factors between 1.0 to 1.3. Beyond that, I can easily detect hot-spotting; and at 2.0 gain factor or higher, I find the hot-spots to be unbearable and bothersome. For HDR, however, due to the lack of brightness produced by any projector for HDR purposes, a screen gain of around 1.3 to 1.6 is highly recommended. Stewart's StudioTek 130 G3 is the film industry's de-facto standard for HDR. If you want a grey screen, Screen Innovations' Slate 1.2 gain screen is also a great option. Bear in mind, however, that any grey screen, regardless of brand, will have a slight blue tint shift, making proper calibration even more necessary than ever.
In Part 3 next week, I'll look at screen aspect ratio. Stay tuned.