Feature found in front projectors designed to compensate for mounting situations when the centerline of the projector's lens is not perpendicular to the screen to allow greater mounting flexibility.
Keystone correction makes a projected image rectangular. This can be accomplished by positioning the projector to be perpendicular to the screen. Since it is not always possible, most projectors are equipped with keystone correction that allows the image to be keystone corrected (made rectangular) by adjusting optics, making mechanical adjustments, or applying digital correction to the image. Keystone correction can be one- or two-dimensional and manual or automatic, depending on the projector and the manufacturer.
"Keystoning" is a form of video image distortion that occurs with front projectors if the centerline of the projector's lens is not perpendicular to the screen. Keystoning results in an image which is shaped like a trapezoid rather than a rectangle — the top of the picture is wider than the bottom, or the left side is taller than the right, or vice versa. Most front projectors include "keystone correction" to correct this distortion. Some models have vertical keystone correction, while others include both vertical and horizontal correction. Although keystone correction allows greater mounting flexibility, it is a form of processing which usually has a slight softening and dimming effect on the picture.
A method of correcting a keystoned image.
A projector's ability to correct the effects of "pointing up" or "pointing down" at a screen, enabling the projector user's audience to view a rectangular image rather than one with a wider top or bottom.
a projector's ability to correct the distortion (usually of a wide-top, narrow-bottom effect) of a projected image caused by improper projector to screen angle.
Most decent projectors come with this feature. Keystone correction allows you to change the shape of the image projected. Basically, if the projector is not set straight or what you are projecting onto is at an angle, you can adjust the keystone to make the image seem flat and normal.
Keystone correction means making a projected image rectangular by mechanical (change position), electronic (adjust optics), or digital means. Projectors may have manual or automatic keystone correction, as well as vertical and/or horizontal correction.
"Keystoning" is caused by the projected image not being perpendicular to the screen, causing the sides of the image to distort and become different widths. A projector equipped with keystone correction can automatically correct this image distortion using a negative keystone. Most projectors have a set number of degrees to which this distortion can be corrected.
Using optics design or other methods to apply a "negative" keystone to the image, which will partially cancel the effects of keystoning. If you aim a projector with keystone correction at a screen with the lens level with the middle of the screen, you will not that the image at the bottom is wider than at the top. When the projector is in normal position, pointing upward 10-25 degrees, the resulting image is fairly rectangular.
See Electronic Keystone Correction and Optical Keystone Correction.
The keystone effect happens when you project an image from any angle other than straight onto the projection surface. This results in an image that is not square. Keystone correction controls can digitally compensate for this offset to produce a square image. Many smaller portable projectors offer just vertical correction to compensate for projector tilt, but some also offer horizontal correction if the projector is off to one side of the screen.
Keystone correction, colloquially also called keystoning, is a function that allows multimedia projectors that are not placed perpendicular to the horizontal centreline of the screen (too high or too low) to skew the output image, thereby making making it rectangular. Without such correction the image will appear as a horizontal trapezoid, the shape of an architectural keystone; hence the name of the feature.