Optics: image projectors – Distortion compensation
Reexamination Certificate
2000-05-03
2003-01-28
Dowling, William (Department: 2851)
Optics: image projectors
Distortion compensation
C348S746000, C353S121000
Reexamination Certificate
active
06511185
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to methods and apparatus for projecting electronically stored images, and more particularly to methods and apparatus for electronically compensating a projected image.
BACKGROUND OF THE INVENTION
Typically, when a digital image is projected onto a wall using a projector the projected image appears slanted (i.e. not a perfect rectangle) as the axis of the light source is not perpendicular to the projection wall or screen. For example, the projector may be placed on a table so that the image is projected upwards onto a wall or screen, or may be mounted on a ceiling so that the image is projected downwards onto a wall or screen. This can result in a “pyramidal effect.” With the increased use of stored digital images and digitally converted or processed images from other media such as films, negatives, etc, projecting the images, for example, directly from a laptop computer or another image source becomes very convenient. However, if not compensated properly either by a mechanical or by an electrical/electronic means—the pyramidal effect becomes very pronounced especially when the projected image is large, thereby making the distortions more problematic.
Several mechanical solutions have been proposed. One solution involves tilting the screen to be perpendicular to the projection axis of the projector. However, this requires the expense and manipulation of a special tiled screen. Oftentimes, only flat walls or flat screens are available. In addition, optical solutions have been proposed that require a projector to have special lens arrangements to compensate for the pyramidal effect. However, such optical lens arrangements can be very expensive and can add to the weight and cost of projectors. In addition, different lenses may be required for different projector types.
In addition, graphics processors are known which perform ratiometric expansion on finally rendered information from a frame buffer and then output the ratiometrically expanded (scaled) image on a display device such as a laptop display or other suitable display. However, the scaled image is typically not re-stored in the frame buffer for display. In addition, the ratiometric expansion provides the same amount of scaling applied to every display line. Accordingly, such ratio metric expanders are typically not adapted for pyramidal effect compensation.
Another optical solution that may be used includes the use of a mirror to provide a reflection at an angle perpendicular to the display surface. Again, this requires special lens construction.
Consequently, a need exists for a method and apparatus to compensate a projected image that provides electronic compensation to allow compensation of the image at the source.
REFERENCES:
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patent: 5548357 (1996-08-01), Appel et al.
patent: 5664858 (1997-09-01), Woo
patent: 5752758 (1998-05-01), Woo
patent: 5795046 (1998-08-01), Woo
patent: 6305805 (2001-10-01), Liebenow
ATI International SRL
Dowling William
Vedder Price Kaufman & Kammholz
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