What's the first thing that comes to mind when you think of digital signage? If it's a flat panel LCD or plasma display hanging in some public place like a retail store, corporate lobby or museum, you wouldn't be alone. For most indoor digital signage networks, these two display technologies dominate the landscape.

However, they aren't the only solution, and in some cases they might not even be the best or most affordable solution. Equally appropriate in some circumstances are projected images played back from the same sort of media server as those used to drive LCD and plasma panels.

Video projectors offer some advantages over flat panel displays. For instance, in terms of price per square inch of display, LCD and plasma panels can't compete. In other words, projectors, which can produce much bigger images than LCDs and plasmas, can be significantly less expensive than the largest flat panels per square inch of displayed image.

Additionally, projectors can create images in unexpected places or ways that are sure to grab the attention of those nearby. For example, some projectors can be used to project onto fog to create an ethereal look that just can't be recreated with flat panels.

Traditionally, projectors haven't been used widely in digital signage applications for at least a couple of important reasons. First, there's the problem with high ambient light. In full daylight conditions, the relatively dim projected light withers, creating a washed- out look at best, and at worst a completely unviewable picture. That's why you're far more likely to find them being used in settings where there's a high degree of control over ambient light, such as in museums.

Another traditional objection to using projectors for digital signage is the relatively narrow range from which they can work to create plumb and square images. In a retail setting, where a store owner doesn't want the public accidentally coming into contact with the projector, working in that useable projection range can often be nearly impossible. That's not to say that projectors aren't built with circuitry to correct keystoned images, but rather that the only placement option in a retail setting may be well out of the area where keystone correction will work.

Fortunately for those who wish to consider projection as a realistic alternative to flat panel displays, the traditional limitations of projectors -high ambient light and projector placement limitations- are vanishing.

Making practical their use in high ambient light environments is a whole new generation of projection screen technology that intelligently accepts the projected light for reflection to the eyes of viewers but rejects ambient light reflection. So successful is this technology that demonstrations of the new screens have been done in the atriums of large retail centers with light streaming in from glass ceilings and at hotel hospitality suites during trade shows where the curtains are thrown wide open during the day.

Correcting for extreme geometric distortions is now possible and affordable thanks to new computer software applications that can be used to determine the severity of distortion and automatically correct the geometry This is no small feat, given where projectors in retail stores must be placed to remain safe from the public. Still, such geometric distortion engines can make the necessary compensation, and in some cases give their users such a high degree of control that images can actually be wrapped around cylinders or onto globes.

Will video projectors replace LCD and plasma panels as the dominant display technology in digital signage networks? Probably not. That said, given the rapid advancements in technology needed to overcome their limitations for digital signage networks, it is a smart idea for anyone planning a digital signage network to consider how projectors might make sense.