Automatic keystone correction system and method
View Patent ↗A projector assembly and method for automatically correcting keystone distortion includes an image correction engine, a light engine, a projection lens having a projection axis, a processor, a directional sensor and an inclination sensor. The sensors determine the absolute vertical and horizontal direction of the projection axis. The inclination sensor determines the vertical zero reference. The direction sensor is used to determine the horizontal zero reference. The processor calculates vertical and horizontal difference angles between the absolute directions and zero reference values in the vertical and horizontal directions. Using difference angles, the processor calculates the keystone distortion and instructs the image correction engine to apply geometric and brightness correction to the image data proportional and inverse to the keystone distortion and lens parameters (field of view, focal length, imperfections, etc) such that the image projected onto a viewing screen, is free from keystone distortion.
1. A projection method for automatically correcting keystone distortion within an optical image that is projected onto a projection surface through a projection lens having a projection axis that is oriented in a direction that is off-axis from the surface normal of the projection surface, said projector method comprising the steps of:
(a) obtaining input image data representing the optical image to be displayed;
(b) determining the absolute horizontal direction of the projection axis, the absolute vertical direction of the projection axis, a vertical zero reference and a horizontal zero reference by:
(i) positioning a directional device against the projection surface, said directional device being adapted to provide a data signal that contains the horizontal zero reference;
(i) receiving the data signal from the directional device and determining the horizontal zero reference from the data signal;
(c) calculating the vertical difference angle by subtracting the vertical zero reference from the absolute vertical direction of the projection axis and the horizontal difference angle by subtracting the horizontal zero reference from the absolute horizontal direction of the projection axis;
(d) determining the keystone distortion based on the vertical difference angle and the horizontal difference angle; and
(e) applying geometric correction to the image data proportional and inverse to said keystone distortion such that the projected image is free from keystone distortion.
2. The projection method of claim 1 , wherein the determination of the vertical zero reference in (b) consists of determining the constant vector of acceleration due to gravity.
3. The projection method of claim 1 , wherein determination of the vertical zero reference in (b) is accomplished by positioning the projection lens in a substantially horizontal perpendicular direction and instantaneously measuring the horizontal direction and recording it as the horizontal zero reference.
4. The projection method of claim 1 , wherein the projection surface is curved and wherein the method further includes concatenating the distortions caused by the shape of the projection surface with said keystone distortion, and applying a correction to the image data that is proportional and inverse to the combined distortions, such that, the resulting projected image is visually distortion free.
5. The projection method of claim 1 , wherein the method further includes concatenating the distortions caused by zooming variations, including changes in the field of view, size of the distortions, and location of a micro-display device relative to the projection surface with said keystone distortion, and applying a correction to the image data proportional and inverse to the combined distortions, such that the resulting projected image is visually distortion free.
6. The projection method of claim 1 , wherein (b) further comprises determining the absolute horizontal direction of the projection axis using a magneto-resistive compass device.
7. The projection method of claim 1 , wherein (b) further comprises determining the absolute horizontal direction of the projection axis using an inertial device.
8. A projection assembly for automatically correcting keystone distortion within an optical image that is projected onto a projection surface based on image data, said projector assembly comprising:
(a) a projection lens having a projection axis that is oriented in a direction that is off-axis from the surface normal of the projection surface;
(b) an inclination sensor coupled to the projection lens in a fixed manner for measuring the absolute vertical direction of the projection axis and a vertical zero reference and a directional sensor coupled to the projection lens and to the inclination sensor in a fixed manner for measuring the absolute horizontal direction of the projection axis;
(c) an input communications device for receiving a horizontal zero reference;
(d) a directional device adapted to be positioned against the projection surface, said directional device including a direction sensor for measuring the horizontal zero reference and signaling means for providing said input communication device with a data signal that includes the horizontal zero reference;
(e) a processor coupled to said directional sensor, said inclination sensor, and said input communications device, said processor being adapted to determine the vertical difference angle by calculating the difference between the absolute vertical direction of the projection axis and the vertical zero reference and the horizontal difference angle by calculating the difference between the absolute horizontal direction of the projection axis and the horizontal zero reference and further adapted for calculating the keystone distortion based on the vertical difference angle and the horizontal difference angle;
(f) an image correction engine applying geometric correction to the image data proportional and inverse to said keystone distortion such that the projected image is free from keystone distortion.
9. The projector assembly of claim 8 , wherein the vertical zero reference is the constant vector of acceleration due to gravity.
10. The projection assembly of claim 8 further comprising an external data processing device selected from the group consisting of: a computer, a handheld personal digital assistant, an infrared remote control unit, said external data processing device being adapted to provide said at least one of said vertical zero reference and said horizontal zero reference to said communication device.
11. The projection assembly of claim 8 , wherein the projection surface is curved, and wherein said processor is further adapted to concatenate the distortions caused by the shape of the projection surface with said keystone distortion, and to apply a correction to the image data that is proportional and inverse to the combined distortions, such that, the resulting projected image is visually distortion free.
12. The projection assembly of claim 8 , wherein said processor is further adapted to concatenate the distortions caused by zooming variations, including changes in the field of view, size of the distortions, and location of a micro-display device relative to the projection surface with said keystone distortion, and to apply a correction to the image data proportional and inverse to the combined distortions, such that the resulting projected image is visually distortion free.
13. The projection assembly of claim 8 , wherein the directional sensor is a magneto-resistive compass device.
14. The projection assembly of claim 8 , wherein the directional sensor is an inertial device.