# US 8,540,375 B2 · Offset projection distortion correction

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- Number: US 8,540,375 B2
- Document ID: US8540375B2
- Status: Granted
- Kind: B2
- Application number: 11/948,811
- Filed: 2007-11-30
- Published: 2009-06-04
- Granted: 2013-09-24
- Earliest claimed: 2007-11-30
- Assignees: Texas Instruments Incorporated
- Applicants: Patrick Rene Destain
- Inventors: Patrick Rene Destain
- Web page: https://patentgrep.com/patent/US8540375B2

## CPC

- G03B 21/28: Reflectors in projection beam {(in illumination beam G03B21/2066)}
- G03B 21/10: Projectors with built-in or built-on screen
- G03B: APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR (optical parts of such apparatus G02B; photosensitive materials or processes for photographic purposes G03C; apparatus for processing exposed photographic materials G03D)

## Abstract

A system and method for correcting optical distortion in an off-axis system is provided. The offset between the center of a display plane and the optical axis of the projection lens system is configured such that the offset is greater than half the vertical dimension of the display plane. In this manner, the distortion, such as a pincushion-type or barrel-type of distortion, is not symmetrical about the horizontal axis. In this scenario, the display plane, the projection lens system, a folding mirror, and/or the spatial light modulator may be tilted such that a keystone effect is induced. This keystone effect may be used to offset the distortion, particularly the pincushion-type or barrel-type of distortions.

## Claims

### Claim 1

A rear-projection image display system, comprising:
a display screen having a display plane with a vertical height and a vertical height center;
a folding mirror;
a projection system having a projection optical axis; and
a housing enclosing the display plane, folding mirror and projection system;
wherein the folding mirror is positioned relative to the display plane and the projection system for folding the projection optical axis by reflecting light projected rearwardly from the projection system onto itself and onto the display plane;
wherein the projection system is positioned relative to the display plane with a vertical offset between the projection optical axis and the vertical height center of the display plane by an optical offset that is about one-half or greater than the vertical height of the display plane; and
wherein the display plane is tilted relative to a plane orthogonal to the projection optical axis by a vertical offset angle to induce a keystone distortion in the displayed image which substantially compensates for a pincushion or barrel distortion in the orthogonal plane.

### Claim 2 (depends on 1)

The system of claim 1, wherein the optical offset is about one-half the vertical height.

### Claim 3 (depends on 1)

The system of claim 1, wherein the vertical offset angle is about 0.12°.

### Claim 4 (depends on 1)

The system of claim 1, wherein the keystone distortion is a negative keystone distortion that substantially compensates for a pincushion distortion in the orthogonal plane.

### Claim 5 (depends on 1)

The system of claim 1, wherein the keystone distortion is a positive keystone distortion that substantially compensates for a barrel distortion in the orthogonal plane.

### Claim 6 (depends on 1)

The system of claim 1, wherein the induced keystone distortion is determined by the relationship:
Dis
⁡
(
%
)
≈
100
*
(
1
-
η
⁢
cos
⁡
(
θ
⁢
⁢
max
)
*
cos
⁡
(
θ
⁢
⁢
keystone
)
cos
⁡
(
θ
⁢
⁢
max
+
θ
⁢
⁢
keystone
)
)
;
where θmax is one-half a field of view of a projection lens of the projection system from the projection system optical axis to a top of a displayed image vertical field of view; η is a factor dependent upon a display screen format (f>1) and offset in % defined by
η
~
100
*
f
2
*
offset
;
and θkeystone is the vertical offset angle.

### Claim 7 (depends on 2)

The system of claim 2, wherein the vertical offset angle is about 0.12°.

### Claim 8 (depends on 7)

The system of claim 7, wherein the keystone distortion is a negative keystone distortion that substantially compensates for a pincushion distortion in the orthogonal plane.

### Claim 9 (depends on 7)

The system of claim 7, wherein the keystone distortion is a positive keystone distortion that substantially compensates for a barrel distortion in the orthogonal plane.