January 09, 2006

Tools for Square Projected Images

Video projectors are unique in that they can cast images on any surface. It doesn't matter if that surface is square, round, textured, or whatever you can imagine. Projected images can often be seen as an attention getting display outside local restaurants, or even on a skyscraper downtown. In applications like these, a square image is not critical. But for a big presentation in your boardroom, or in a home theater, a square image is essential. So what features help you achieve a perfectly aligned image? Read on.

There are two features available that help you create a square image with your video projector. Keystone correction and lens shift. Not all projectors come with one, or both, of these features. Here is a quick look at the two features.

Keystone Correction

Today, there are two methods of keystone correction, manual and digital. Manual keystone correction is essentially a physical adjustment to the lens of the projector, outside of the casing. The manual adjustment works well in some situations, but cannot eliminate horizontal keystoning. This kind of correction typcially comes by way of adjustable feet under the projector. Most projectors without digital correction will offer at least this feature.

LCD and DLP™ projectors are both digital display devices. Data such as a PowerPoint™ presentation sent to a projector, is digitally converted and scaled. By adding a special selectable algorithm to the scaling, some new projectors are able to correct the image before it reaches the projection lens. The result is a squared image, even at an angle. This allows presenters more flexibility when setting up their projector in variable environments. Digital keystone correction is available on the Panasonic PT-LB20U.

Quick Tip: Projectors vary in the amount of keystone correction they can provide. For vertical (up and down) keystone correction, some offer a modest 12 degrees while others achieve as much as 35 degrees of correction.

What is Lens Shift?

Lens shift provides space to move the lens itself left and right or up and down within the projector housing. This adjustment can be made either manually with a dial or joystick, or by pressing the menu buttons. This extra space to reposition the lens means greater leeway in the placement of a projector in a room.

For example, imagine looking at a picture on your wall. Now imagine your picture moving up or down so that the top of the image is now located where the center of the image used to be. A projector with lens shift can make an adjustment like this without requiring you to physically move the projector. Rather, the lens inside the projector housing is moving to create the effect. This feature is available on the the Panasonic PT-AE900U and the Panasonic PT-D5500U.

There are a few different kinds of lens shift. Some projectors can perform one kind of shift, most often vertical, while other projectors offer a broader range of motion including vertical, horizontal, and variable (diagonal) movement. Some projectors include a manual lens shift while others feature power adjustment. Power lens shift can sometimes be controled by the remote control, which is an added convenience.

Keystone Correction vs. Lens Shift

Digital Keystone Correction is a great feature for power presenters. However, using lens shift to correct an image will produce better looking images. Why? Because when you use digital keystone correction, the image undergoes a compression and conversion that recreates edge pixels, sometimes causing noticeable artifacts along the corrected portion of the image. Keystone correction works well with still images, and well enough with video in a temporary setting. In a permanent installation, using lens shift will produce the best images.

Quick Tip: While keystone correction is a handy feature for road warriors and other portable projector users, it does not produce an ideal picture quality. Scaling inside the projector creates a slightly distorted image, particularly at the sides of the screen. In a long-term installation, lens shift is preferred to keystone correction.

Still have questions? Call a Projector Expert today for the best advice and the best price on projectors for work and home.

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