Keystoning and focus correction for an overhead projector

Details Keystoning and focus correction for an overhead projector Keystoning and focus correction for an overhead projector

1995-06-06

1996-08-20

Dowling, William C.

Optics: image projectors

Distortion compensation

353 70, G03B 2100

Patent

active

055483577

ABSTRACT:
In order to correct for keystoning distortion when projecting a transparency onto a projection screen, computer software is used to deliberately distort an electronic image. A transparency, which can be a slide or a projection panel display such as an LCD panel, is then produced with the intentionally distorted image. The oblique angle between the horizontal plane through the projector and the viewing screen is compensated for by an inverse tapered compression of the electronic image. In one embodiment, a test slide is generated with a plurality of non parallel line pairs, each line pair representing a different distortion correction to an image. The test slide is projected to the screen to be used. A pair of line pairs most parallel to each other is identified. The line pair identification is used to activate the portion of software which generates that particular image distortion. In another embodiment, focus distortion is corrected by placing the transparency on an easel whose angle, relative to the horizontal, is adjustable. The angle of final projection is selected to obtain optimum focus on the screen.

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patent: 5414480 (1995-05-01), Morizumi
patent: 5422691 (1995-06-01), Ninomiya et al.

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