Three shades of black: projector screen colour
Time for a chat about projector screen colour.
Who would have thought in the late 1800s when the first “magic lantern” saw the light of day (no pun intended) that over 200 years later we would still project moving images onto a surface and be in awe? The first professionals to find practical use for the first projector were magicians and entertainers. I guess nothing much has changed….
One of the holy grails in projection is how black the “colour” black can be. As we are projecting light on a white surface, and the light is then reflected on our retina, black can never be really black. Black is an absence of light reflected on a white surface. So black becomes….dark grey, sort of. Unless, of course, you change the projection screen fabric colour from white to….black (or grey)! At Rapallo, we have been supplying projection screens for over a decade. We have had a great relationship with our supplier. So when they sent us their new grey acoustic transparent projection fabric, we jumped at the opportunity to test it and see what the difference was. The results are interesting, to say the least.
While information about the technology of early cinemas is readily available, information about the screens onto which early films were projected is far harder to come by. It is odd that comparatively little attention has been paid to projection screens over the years. The type and quality of the screen so clearly affects a film viewing experience in a number of ways. The clarity, brightness, colour and contrast of the image are all crucially important to many as is the absence of distracting imperfections such as marks on a screen’s surface.
Brightness beyond projector screens
‘Apparent contrast’ in a projected image is the perceived brightness difference between the darkest and lightest areas of a subject. It is dependent on the ambient light conditions, luminous power of the projector and the size of the image being projected.
This really means that a larger screen size means less luminous power per square meter. And thus it also means less contrast in the presence of ambient light. Despite the fact that projector light is directed at the screen, some light will always be reflected on the walls in the room. As a result, it will increase the ambient light level and thus contribute to the degradation of picture quality.
One of the ways you can counter this, is by decorating the room with dark colours. At Rapallo, our demo room is completely black, just like the Hoyts or Event cinemas. That is the perfect setup, but many households won’t be able to push it that far (My wife definitely didn’t let me get away with a black home theatre at home;-)). A dedicated cinema room potentially could be painted in the most optimal colour for contrast. But as soon as the cinema room is used as a family room during the day, it is highly unlikely that black walls and ceilings will be acceptable. You always have to work with what you have…
When projector manufacturers advertise contrast ratios they measure the light levels with projector on full black / full white, giving as high contrast ratios as possible. A real situation will never be this optimal. Never.
But projectors are only one side of the story. Manufacturers of projector screens have been aware of the issues that are caused by ambient light.
Projector screens
One solution for tackling the problem has been by introducing screen surfaces that direct more of the light towards the audience, rather than it being dispersed around the room. They are called screens with ‘high gain’. It’s a balancing act though because highly reflective screens tend to suffer from hot spots when part of the screen seems much more bright than the rest. Screens with high gain also have a narrower usable viewing angle. And the amount of reflected light rapidly decreases as the viewer moves away from the centre of the screen where the light is channelled towards. So, as with anything in life, it’s a matter of balance.
Gain levels range from 0.8 of to a gain 2.5 of the more highly reflective glass bead screens, approaching a mirror-like effect. If at all possible, in our opinion, a screen gain of 1.0 combined with the use of curtains and dark wall colours will give the best result and is the most economical option. If needed, opt for a projector screen with a higher gain, but we recommend not to go overboard.
But what about the black or grey screens we mentioned earlier? A darker (grey) screen reflects less light, of course—both light from the projector and ambient light. This decreases the ambient light. But unfortunately it also decreases the luminance (brightness) of the projected image. So while the light areas of the projected image are dimmer, the dark areas are darker. White is less bright, but intended black is closer to actual black. But also, contrast gets better. That is why many screen manufacturers appropriately call their grey screens “high-contrast” models.
It’s quite easy to understand that grey screens rely on reasonably powerful projectors that are able to produce adequate levels of luminosity. A powerful projector means that the white areas of the image still appear as white.
This is something we got quite fascinated about recently, so we decided to do some tests with both a white and a grey screen. (We didn’t go as far as testing a black screen)
So these are the results we came up with.
For clarity’s sake, in these photos, the left hand side is the white fabric. The right hand side is the grey fabric. Both fabrics are acoustic transparent. And they are mounted on a 120” fixed frame screen. The white fabric is not under tension. It was just taped to the aluminium frame, in front of the grey screen. It’s by no means a situation that we would use for normal viewing. Rather it was a means to an end to test both fabrics at the same time, with identical conditions, projector settings and images. Call it Kiwi ingenuity, if you must. J
The white screen in the pictures has a screen gain of 1.0, the grey one 0.8.
The images are taken with a Panasonic full frame digital camera (for clarity’s sake; they are untouched by Photoshop). Obviously, they are only an approximation of what our eyes see.
Contrast definitely improves, and black levels are superior,
But the Sony VPL-VW260ES (now replaced with the VPL-VW270ES) projector that we used for the tests, struggled with HDR content. Clearly, 1500 lumens in our room is not enough on a grey screen with gain of 0.8.
This was even more exaggerated when watching 3D content. That is because the camera is taking photos without the 3D glasses in front of its lens. The grey colour of the 3D glasses made the experience of low luminosity even worse. So we definitely need a brighter projector than the Sony (which was set to full brightness and high energy light bulb setting).
So….should you go for a grey screen? If you have a dedicated and blacked out theatre room with a bright projector of 1800 lumens or more, we strongly suggest you look into it. Otherwise, it is probably better to stick with white.
Other options to consider are the Screen Innovations screens, who have patented their black diamond screens with a gain of 0.8 and slate grey screens with a gain of 1.2 (as opposed to the grey screen with a 0.8 gain that we tested).