System and method for improved keystone correction

• US 7,705,862 B1
• Filed: 09/15/2006
• Issued: 04/27/2010
• Est. Priority Date: 01/28/2003
• Status: Active Grant

• Current Assignee: Pixelworks Semiconductor Technology Company Limited
• Original Assignee: Pixelworks Incorporated
• Inventors: Teng, Tianbing Brian
• Primary Examiner(s): Chauhan; Ulka
• Assistant Examiner(s): Ricks; Donna J
• Application Number:
  US11/532,358
• Time in Patent Office: 1,320 Days
• Field of Search: 345/647, 715/723, 715/721, 715/719, 715/733
• US Class Current: 345/647
• CPC Class Codes: G03B 21/14 Details
• CPC Class Codes: G03B 27/58 Baseboards, masking frames, or other holders for the sensitive material G03B27/53 takes precedence ; for electrophotographic copiers G03G15/65
• CPC Class Codes: G03B 5/04 Vertical adjustment of lens; Rising fronts
• CPC Class Codes: G06T 5/80 Geometric correction
• CPC Class Codes: G09G 2320/02 Improving the quality of display appearance
• CPC Class Codes: G09G 2320/028 by changing the viewing angle properties, e.g. widening the viewing angle, adapting the viewing angle to the view direction
• CPC Class Codes: G09G 2320/0693 Calibration of display systems
• CPC Class Codes: G09G 2320/08 Arrangements within a display terminal for setting, manually or automatically, display parameters of the display terminal
• CPC Class Codes: G09G 2370/04 Exchange of auxiliary data, i.e. other than image data, between monitor and graphics controller
• CPC Class Codes: G09G 3/001 using specific devices not provided for in groups G09G3/02 - G09G3/36, e.g. using an intermediate record carrier such as a film slide; Projection systems; Display of non-alphanumerical information, solely or in combination with alphanumerical information, e.g. digital display on projected diapositive as background slide projectors per se G03B23/00 = 42 HP
• CPC Class Codes: G09G 3/002 to project the image of a two-dimensional display, such as an array of light emitting or modulating elements or a CRT
• CPC Class Codes: H04N 5/74 Projection arrangements for image reproduction, e.g. using eidophor
• CPC Class Codes: H04N 9/31 Projection devices for colour picture display , e.g. using electronic spatial light modulators [ESLM]
• CPC Class Codes: H04N 9/3185 Geometric adjustment, e.g. keystone or convergence optical or mechanical adjustment of convergence H04N9/317; using scanning means H04N3/22; optical or mechanical adjustments of projectors not peculiar to the presence of an electronic spatial light modulator G03B21/14
• CPC Class Codes: H04N 9/3194 including sensor feedback

Abstract

I describe and claim a system and method for improved keystone correction. The method comprising identifying input values associated with an image projected on the projection surface, the input values including one or more center-points on edges of a distorted projection of the image and including a plurality of corners within the distorted projection of the image, the corners corresponding to an undistorted projection of the image, determining one or more keystone scaling values responsive to the identifying, and predistorting the image responsive to the determining, the predistorted image exhibiting no distortion and aligning with the plurality of corners when projected on the projection surface.

Claims

1. A method comprising:

identifying input values associated with an image projected by a projection system on a projection surface, the input values including a rotation angle of the projection system, one or more center-points located on edges of a distorted image projection, and a plurality of corners within the distorted image projection, the corners corresponding to an undistorted projection of the image;

a keystone driver determining a vertical scaling value VerticalScaler, a vertical increment value VerticalScalingIncrement, a horizontal scaling value HorizontalScaler, and a horizontal increment value HorizontalScalingIncrement based on the input values, wherein the determining comprises applying the following first and second equations;

$\mathrm{InputHeight}=\mathrm{VerticalScaler}+\frac{\mathrm{OutputHeight}<br><br>\left(\mathrm{OutputHeight}-1\right)}{2}\times <br><br>\mathrm{VerticalScalingIncrement};<br><br><br><br>\mathrm{and}$ $\mathrm{InputCenter}=\mathrm{OutputCenter}<br><br>\times <br><br>\mathrm{VerticalScaler}+\frac{\mathrm{OutputCenter}<br><br>\left(\mathrm{OutputCenter}-1\right)}{2}\times <br><br>\mathrm{VerticalScalingIncrement},$

wherein InputHeight comprises a height of the distorted image projection, InputCenter comprises a distance to the center of an edge of the distorted image projection, OutputHeight comprises a height of the undistorted projection of the image, and OutputCenter comprises a distance to the center of an edge of the undistorted projection of the image; and

a keystone corrector predistorting the image responsive to the determining and based on the determined vertical scaling value, vertical increment value, horizontal scaling value, and horizontal increment value, the predistorted image exhibiting no distortion and aligning with the plurality of corners when projected on the projection surface.

2. The method of claim 1 where each center-point is located at a mid-point between two adjacent corners of the distorted image projection.

3. The method of claim 1 including

storing one or more sets of the input values to at least one keystone table according to orientation data received from an interface, the orientation data to identify a configuration of a projection device;

and

retrieving the sets of the input values responsive to the orientation data.

4. The method of claim 1 where the orientation data indicates at least one of an orientation of the projection device relative to the projection surface, a type of optical lens to be used to project the image, and a position associated with zoom functionality.

5. The method of claim 1 where at least one of the sets of input values includes center-points associated with three edges of a distorted projection of the image and four corners corresponding to the undistorted projection of the image.

6. The method of claim 1, wherein the determining further comprises applying the following third and fourth equations:

$\mathrm{InputLength}=\mathrm{HorizontalScaler}+\frac{\mathrm{OutputLength}<br><br>\left(\mathrm{OutputLength}-1\right)}{2}\times <br><br>\mathrm{HorizontalScalingIncrement},<br><br>\mathrm{and}$ $\mathrm{InputCenter}=\mathrm{OutputCenter}<br><br>\times <br><br>\mathrm{HorizontalScaler}+\frac{\mathrm{OutputCenter}<br><br>\left(\mathrm{OutputCenter}-1\right)}{2}\times <br><br>\mathrm{HorizontalScalingIncrement},$

wherein InputLength comprises a length of the distorted image projection and OutputLength comprises a length of the undistorted projection of the image.

7. The method of claim 6 including vertically scaling the image according to the vertical scaling value VerticalScaler and the vertical increment value VerticalScalingIncrement.

8. The method of claim 7 including horizontally scaling the vertically scaled image according to the horizontal scaling value HorizontalScaler and the horizontal increment value HorizontalScalingIncrement.

9. A device comprising:

an interface to ascertain input values associated with an image projected on the projection surface, the input values including one or more center-points on edges of a distorted projection of the image and including a plurality of corners within the distorted projection of the image, the corners corresponding to an undistorted projection of the image;

a keystone driver to determine one or more keystone scaling values responsive to the input values, where the keystone driver is adapted to calculate a vertical scaling value VerticalScaler, a vertical increment value VerticalScalingIncrement, a horizontal scaling value HorizontalScaler, and a horizontal increment value HorizontalScalingIncrement responsive to the corners and the center-points using the following first and second equations;

$\mathrm{InputHeight}=\mathrm{VerticalScaler}+\frac{\mathrm{OutputHeight}<br><br>\left(\mathrm{OutputHeight}-1\right)}{2}\times <br><br>\mathrm{VerticalScalingIncrement};<br><br><br><br>\mathrm{and}$ $\mathrm{InputCenter}=\mathrm{OutputCenter}<br><br>\times <br><br>\mathrm{VerticalScaler}+\frac{\mathrm{OutputCenter}<br><br>\left(\mathrm{OutputCenter}-1\right)}{2}\times <br><br>\mathrm{VerticalScalingIncrement},$

wherein InputHeight comprises a height of the distorted image projection, InputCenter comprises a distance to the center of an edge of the distorted image projection, OutputHeight comprises a height of the undistorted projection of the image, and OutputCenter comprises a distance to the center of an edge of the undistorted projection of the image; and

a keystone corrector to predistort the image responsive to the keystone scaling values, the predistorted image exhibiting no distortion and aligning with the plurality of corners when projected on the projection surface, wherein the keystone corrector comprises;

a vertical scaler to vertically scale the image according to the vertical scaling values; and

a horizontal scaler to horizontally scale the vertically scaled image according to the horizontal scaling values.

10. The device of claim 9 where each center-point is located at a mid-point between two adjacent corners of the distorted projection of the image.

11. The device of claim 9 includes one or more keystone tables to store at least one set of the input values, where the keystone driver stores and retrieves the input values according to orientation data received from the interface, the orientation data to identify a configuration of a projection device.

12. The device of claim 11 where the orientation data indicates at least one of an orientation of the projection device relative to the projection surface, a type of optical lens to be used to project the image, and a position associated with zoom functionality.

13. The device of claim 9

where the keystone driver is adapted to interpolate the keystone scaling values;

and

where keystone corrector is adapted to predistort the image responsive to the interpolated keystone scaling values.

14. The device of claim 9, wherein the keystone driver is further adapted to calculate VerticalScaler, VerticalScalingIncrement, HorizontalScaler, and HorizontalScalingIncrement using the following third and fourth equations:

$\mathrm{InputLength}=\mathrm{HorizontalScaler}+\frac{\mathrm{OutputLength}<br><br>\left(\mathrm{OutputLength}-1\right)}{2}\times <br><br>\mathrm{HorizontalScalingIncrement},<br><br>\mathrm{and}$ $\mathrm{InputCenter}=\mathrm{OutputCenter}<br><br>\times <br><br>\mathrm{HorizontalScaler}+\frac{\mathrm{OutputCenter}<br><br>\left(\mathrm{OutputCenter}-1\right)}{2}\times <br><br>\mathrm{HorizontalScalingIncrement},$

wherein InputLength comprises a length of the distorted image projection and OutputLength comprises a length of the undistorted projection of the image.

15. An apparatus including a computer-readable medium containing instructions, when executed by a processor or multiple communicating processors, perform a method comprising:

identifying input values associated with an image projected on a projection surface, the input values including one or more center-points on edges of a distorted projection of the image and including a plurality of corners within the distorted projection of the image, the corners corresponding to an undistorted projection of the image;

determining a vertical scaling value VerticalScaler, a vertical increment value VerticalScalingIncrement, a horizontal scaling value HorizontalScaler, and a horizontal increment value HorizontalScalingIncrement based on the input values, wherein the determining comprises applying the following first and second equations;

$\mathrm{InputHeight}=\mathrm{VerticalScaler}+\frac{\mathrm{OutputHeight}<br><br>\left(\mathrm{OutputHeight}-1\right)}{2}\times <br><br>\mathrm{VerticalScalingIncrement};<br><br><br><br>\mathrm{and}$ $\mathrm{InputCenter}=\mathrm{OutputCenter}<br><br>\times <br><br>\mathrm{VerticalScaler}+\frac{\mathrm{OutputCenter}<br><br>\left(\mathrm{OutputCenter}-1\right)}{2}\times <br><br>\mathrm{VerticalScalingIncrement},$

wherein InputHeight comprises a height of the distorted image projection, InputCenter comprises a distance to the center of an edge of the distorted image projection, OutputHeight comprises a height of the undistorted projection of the image, and OutputCenter comprises a distance to the center of an edge of the undistorted projection of the image; and

predistorting the image responsive to the determining and based on the determined vertical scaling value, vertical increment value, horizontal scaling value, and horizontal increment value, the predistorted image exhibiting no distortion and aligning with the plurality of corners when projected on the projection surface.

16. The apparatus of claim 15 where each center-point is located at a mid-point between two adjacent corners of the distorted projection of the image.

17. The apparatus of claim 15 including

calculating vertical scaling values responsive to the corners and the center-points;

and

vertically scaling the image according to the vertical scaling values.

18. The apparatus of claim 17 including

calculating horizontal scaling values responsive to the corners and the center-points;

and

horizontally scaling the vertically scaled image according to the horizontal scaling values.

19. The apparatus of claim 15 including

storing one or more sets of the input values to at least one keystone table according to orientation data received from an interface, the orientation data to identify a configuration of a projection device;

and

retrieving the sets of the input values responsive to the orientation data.

20. The apparatus of claim 15 where the orientation data indicates at least one of an orientation of the projection device relative to the projection surface, a type of optical lens to be used to project the image, and a position associated with zoom functionality.

21. The apparatus of claim 15 where at least one of the sets of input values includes center-points associated with three edges of a distorted projection of the image and four corners corresponding to the undistorted projection of the image.

22. The apparatus of claim 15, wherein the determining further comprises applying the following third and fourth equations:

$\mathrm{InputLength}=\mathrm{HorizontalScaler}+\frac{\mathrm{OutputLength}<br><br>\left(\mathrm{OutputLength}-1\right)}{2}\times <br><br>\mathrm{HorizontalScalingIncrement},<br><br>\mathrm{and}$ $\mathrm{InputCenter}=\mathrm{OutputCenter}<br><br>\times <br><br>\mathrm{HorizontalScaler}+\frac{\mathrm{OutputCenter}<br><br>\left(\mathrm{OutputCenter}-1\right)}{2}\times <br><br>\mathrm{HorizontalScalingIncrement},$

wherein InputLength comprises a length of the distorted image projection and OutputLength comprises a length of the undistorted projection of the image.

23. A device comprising:

means for identifying input values associated with an image projected on a projection surface, the input values including one or more center-points on edges of a distorted projection of the image and including a plurality of corners within the distorted projection of the image, the corners corresponding to an undistorted projection of the image;

means for determining vertical scaling value VerticalScaler, a vertical increment value VerticalScalingIncrement, a horizontal scaling value HorizontalScaler, and a horizontal increment value HorizontalScalingIncrement based on the input values, wherein the means for determining comprises applying the following first and second equations;

$\mathrm{InputHeight}=\mathrm{VerticalScaler}+\frac{\mathrm{OutputHeight}<br><br>\left(\mathrm{OutputHeight}-1\right)}{2}\times <br><br>\mathrm{VerticalScalingIncrement};<br><br><br><br>\mathrm{and}$ $\mathrm{InputCenter}=\mathrm{OutputCenter}<br><br>\times <br><br>\mathrm{VerticalScaler}+\frac{\mathrm{OutputCenter}<br><br>\left(\mathrm{OutputCenter}-1\right)}{2}\times <br><br>\mathrm{VerticalScalingIncrement},$

wherein InputHeight comprises a height of the distorted image projection, InputCenter comprises a distance to the center of an edge of the distorted image projection, OutputHeight comprises a height of the undistorted projection of the image, and OutputCenter comprises a distance to the center of an edge of the undistorted projection of the image; and

means for predistorting the image responsive to the determining and based on the determined vertical scaling value, vertical increment value, horizontal scaling value, and horizontal increment value, the predistorted image exhibiting no distortion and aligning with the plurality of corners when projected on the projection surface.

24. The method of claim 23 where each center-point is located at a mid-point between two adjacent corners of the distorted projection of the image.

25. The method of claim 23 including

means for calculating vertical scaling values responsive to the corners and the center-points;

and

means for vertically scaling the image according to the vertical scaling values.

26. The method of claim 25 including

means for calculating horizontal scaling values responsive to the corners and the center-points;

and

means for horizontally scaling the vertically scaled image according to the horizontal scaling values.

27. The method of claim 23 including

means for storing one or more sets of the input values to at least one keystone table according to orientation data received from an interface, the orientation data to identify a configuration of a projection device;

and

means for retrieving the sets of the input values responsive to the orientation data.

28. The method of claim 23 where the orientation data indicates at least one of an orientation of the projection device relative to the projection surface, a type of optical lens to be used to project the image, and a position associated with zoom functionality.

29. The method of claim 23 where at least one of the sets of input values includes center-points associated with three edges of a distorted projection of the image and four corners corresponding to the undistorted projection of the image.

30. The device of claim 23, wherein the means for determining further comprises applying the following third and fourth equations:

$\mathrm{InputLength}=\mathrm{HorizontalScaler}+\frac{\mathrm{OutputLength}<br><br>\left(\mathrm{OutputLength}-1\right)}{2}\times <br><br>\mathrm{HorizontalScalingIncrement},<br><br>\mathrm{and}$ $\mathrm{InputCenter}=\mathrm{OutputCenter}<br><br>\times <br><br>\mathrm{HorizontalScaler}+\frac{\mathrm{OutputCenter}<br><br>\left(\mathrm{OutputCenter}-1\right)}{2}\times <br><br>\mathrm{HorizontalScalingIncrement},$

wherein InputLength comprises a length of the distorted image projection and OutputLength comprises a length of the undistorted projection of the image.