Angles Of Reflection

One of the many benefits projection screens offer compared to other types of displays is their flexibility in design.  Granted, most screens in the world take the form of some variety of rectangle but there is no reason why they need to be restricted to that one basic shape.  All sorts of shapes are possible and one popular variation on the standard is a curved screen.

Curved Screens

As a specialty product, a curved screen is rather interesting.  It is automatically a more eye-catching design compared to most displays, simply because it is different from the more typical televisions, billboards, posters, monitors and any other flat rectangle we might happen to see virtually everywhere we look.  

For digital signage, this differentiation of form can be a real boon.  Enticing people to look at the content of an advertisement by delivering it through unconventional means is a great way to get the message across to consumers.  Beyond the novelty, a curved screen can add a very practical benefit in that it is easier to see at least some portion of the screen from a variety of angles, rather than just from a range of positions in front of the screen.

Curved screens can also be put to good use in the field of simulation.  Whether for avionics, military, or even for medical use or in museums of any kind, the ability of a curved screen to envelop the viewer can be quite valuable.  In fact, it is possible to extend a curve into a complete circle to create an entire 360° panorama for a completely immersive environment.

In light of these applications for a curved screen, it may be tempting to use them in other areas as well.  It certainly may be possible to do so in some cases but there are a few points of caution worth mentioning.

The first point to consider is the matter of the projection geometry.  On a flat screen, it is a fairly simple matter of using a projector’s zoom function and the physical location of both the projector and screen to arrive at an image that fills the screen and terminates in nice, square edges.  A curved screen, on the other hand, presents an unusual challenge because not all portions of the screen are the same distance from the projector.

The reason this is a problem is that the size of an image on a screen will increase just as the distance between the screen and projector increases.  A pixel on the edge of the screen will not be the same size as one in the center of the screen’s curve.  This is most noticeable at the very top and bottom of the image, which will bow outwards like a pincushion instead of running parallel to each other and perpendicular to the vertical edges.  Fortunately, image warping software and special lenses can bring the image back into square, though these solutions do contribute to the overall cost.

A more subtle artifact of a non-flat projection surface is that the shape of a pixel will no longer be square.  This is another expression of the correlation between distance and size, outlined above, but on a much smaller scale.  Admittedly, non-square pixels would probably go completely unnoticed in most cases, save for a home theater or any other environment where perfect performance is expected.

Another potential difficulty is that of uniform focus.  The degree to which this is objectionable will depend on the precise nature of the projector’s optical system.  Basically, when a projector is “in focus”, there is often a bit of room in front of and behind the screen that would also qualify as being so.  This range is commonly known as depth of field and a curved screen will certainly benefit from a lens system that is relatively deep in this respect.

Beyond these video considerations, the introduction of any curved surface to a room can present a significant challenge to proper acoustics.  The basic problem is that this sort of shape is excellent at focusing sound waves in ways that flat surfaces cannot.  In practical terms, this means that any source of sound in front of the screen – rear channel speakers, especially – is in danger of sounding inordinately loud from certain positions. 

Not all is lost for curved screens, however, despite the stipulations outlined above.  Integration of any piece of equipment requires some level of compromise, after all.  The important thing is to understand what the restrictions and benefits are for each piece of equipment so that the overall system can perform as expected. 

While it is true that curved screens need a little extra thought and possibly some extra hardware or software to really shine, none of the challenges they present are insurmountable.  The key, again, is weighing the costs against the benefits to arrive at a solution that serves the user’s needs without going “around the bend”.

-- Adam Teevan
    ateevan@da-lite.com

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