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What is keystone correction?
"Keystone distortion" occurs when the projector is not vertically aligned to the screen, or when the projection screen has an inclined surface. The image generated by one of these misaligns will look trapezoid instead of square. A distorted image is a distraction that most presenters want to avoid. However, in some cases, there is no other place to put the projector. So, what can you do?
Early projectors did not have keystone correction. Projectors are usually found in fixtures, so furniture and screens can be moved to fit. As projectors become lighter and more portable, the need for simpler solutions grows.
Manual keystone correction
Today, there are two keystone correction methods, manual and digital. Manual keystone correction is basically the physical adjustment of the projector lens to project at a higher or lower Angle than on a flat surface. Manual adjustment works well in some cases but does not eliminate the horizontal trapezoid distortion. The projector also needs to be away from the screen to be effective. Not good enough, you say? Read on...
Digital keystone correction
Both LCD and DLP™ projectors are digital display devices. Data such as PowerPoint presentations sent to the projector are digitally transformed and scaled. By adding special selectable algorithms to the zoom, some new projectors are able to change the image before it reaches the projected lens. The result is to square the image, even at an Angle. This allows the presenter more flexibility in setting up the projector in a variable environment.
Correction degree
Projectors can provide different keystone distortion correction amounts. For vertical (up and down) keystone corrections, some offer a moderate 12 degrees, while others offer corrections of up to 35 degrees. Some new projectors, such as the latest Hitachi projector line-up, also offer level (side to side) keystone correction.
Although keystone correction is a convenient feature for road warriors and other portable projector users, it does not produce the desired image quality. Scaling inside the projector produces a slightly distorted image, especially on both sides of the screen. Lens shift is superior to keystone correction in long-term installation.
