Calibration based on intrinsic parameter selection and a projected calibration target

• US 10,395,389 B2
• Filed: 04/11/2016
• Issued: 08/27/2019
• Est. Priority Date: 04/11/2016
• Status: Active Grant

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Inventors: Pollard, Stephen
• Primary Examiner(s): Lee, Y
• Application Number:
  US15/096,121
• Publication Number:
  US 20170294009A1
• Time in Patent Office: 1,233 Days
• CPC Class Codes: G06T 7/80 Analysis of captured images to determine intrinsic or extrinsic camera parameters, i.e. camera calibration
• CPC Class Codes: H04N 17/002 for television cameras

Abstract

A computing system includes a projector, a camera, a calibration target, and a processor. The calibration target has known dimensions and four corners in a fixed position relative to both the projector and the camera. The processor causes the projector to project a calibration image having four corners and a repetitive pattern. The processor further causes the camera to capture a captured image of the calibration image and determine a rotation and translation that brings the four corners of the captured image into correspondence with the four corners of the calibration target and identify internal corner points of the repetitive pattern. The processor further selects an intrinsic parameter value and calibrates a 3D coordinate system of at least one of the camera and the projector to the calibration target using the selected intrinsic parameter value, the rotation and translation, and the internal corner points.

Claims

1. A computing system, comprising:

a projector;

a camera;

a calibration target of known dimensions defining a real world coordinate frame and having four corners, wherein the projector and the camera are in a fixed position relative to the calibration target; and

a processor to;

cause the projector to project an image of uniform brightness, wherein the image of uniform brightness is to determine a projection area;

cause the camera to capture a first captured image of the image of uniform brightness;

cause the projector to project a calibration image having four corners and a repetitive pattern to provide location information in the real world coordinate frame of one of the projector and the camera relative to the calibration target onto the calibration target;

cause the camera to capture a second captured image of the calibration image;

determine a rotation and translation that brings the four corners of the second captured image into correspondence with the four corners of the calibration target;

identify internal corner points of the repetitive pattern in the captured image;

select an intrinsic parameter value from a set of intrinsic parameter values based on a comparison of the effect of each of the intrinsic parameter values in the set applied to information related to the calibration target, the first captured image, and the second captured image;

calibrate a 3D coordinate system of at least one of the camera and the projector to the real world coordinate frame of the calibration target using the selected intrinsic parameter value, the rotation and translation, and the internal corner points, wherein the 3D coordinate system is associated with the calibration target, wherein the 3D coordinate system comprises a vertical z-axis from the center of the calibration target, and a horizontal x-axis and horizontal y-axis along the surface of the calibration target; and

output information related to the 3D coordinate system.

2. The computing system of claim 1, wherein the calibration target comprises an input device.

3. The computing system of claim 1, wherein the calibration target comprises a flat and rectangular calibration target.

4. The computing system of claim 1, wherein the processor is further to receive information about the set of intrinsic parameter values from at least one of a network and a storage and wherein the set of intrinsic parameter values are related to a calibration of a separate device.

5. The computing system of claim 1, wherein the intrinsic parameter comprises at least one of:

camera focal length, camera aspect ratio, camera radial distortion, camera center of camera, projector center of projection, projector focal length, projector aspect ratio, and projector radial distortion.

6. The computing system of claim 1, wherein causing the projector to project a calibration image comprises causing the projector to project a first image including a pattern with the repetitive pattern of the calibration image and to project a second image of uniform brightness with the four corners of the calibration image.

7. A method, comprising:

capturing a first captured image and a second captured image, by a camera, of a calibration target of known dimensions defining a real world coordinate frame and having four corners, wherein a projector and a camera are in a fixed position relative to the calibration target, wherein the projector is to project an image of uniform brightness to determine a projection area and a calibration image having four corners and a repetitive pattern onto the calibration target to provide location information in the real world coordinate frame of one of the projector and the camera relative to the calibration target, wherein the first captured image is of the image of uniform brightness and the second captured image is of the calibration image;

determining a rotation and translation that brings the four corners of the second captured image into correspondence with the four corners of the calibration target;

identifying the internal corner points of the repetitive pattern in the second captured image;

determining first calibration information associated with a first intrinsic parameter value based on a comparison of the calibration target to the first captured image and the second captured image by associating the first intrinsic parameter value with a device comprising at least one of the camera and the projector;

determining second calibration information associated with a second intrinsic parameter value based on a comparison of the calibration target to the second captured image by associating the second intrinsic parameter value with the device;

selecting the first intrinsic parameter value based on a comparison of the first calibration information and the second calibration information;

calibrating a 3D coordinate system of the device to the real world coordinate frame of the calibration target using the selected first intrinsic parameter value, the rotation and translation, and the internal corner points, wherein the 3D coordinate system is associated with the calibration target, wherein the 3D coordinate system comprises a vertical z-axis from the center of the calibration target, and a horizontal x-axis and horizontal y-axis along the surface of the calibration target; and

outputting information related to the 3D coordinate system.

8. The method of claim 7, wherein the set of intrinsic parameter values comprises intrinsic parameter values associated with a factory calibration of another device.

9. The method of claim 7, wherein the calibration target comprises an input device.

10. The method of claim 7, wherein determining the first calibration information comprises determining a residual error associated with the first calibration parameter value.

11. A computer readable non-transitory storage medium comprising instructions executable by a processor to:

create 3D calibration information for a device, comprising at least one of a projector and a camera that are in a fixed position relative to a calibration target, based on a set of intrinsic calibration parameter value options, the calibration target that comprises known dimensions that define a real world coordinate frame and four corners in a fixed position relative to both the projector and the camera, and a first captured image and a second captured image captured by the camera, wherein the first captured image is of an image of uniform brightness projected by the projector and the second captured is of a calibration image projected by the projector, wherein the calibration image has four corners and a repetitive pattern to provide location information in the real world coordinate frame of one of the projector and the camera relative to the calibration target onto the calibration target, wherein creating 3D calibration information comprises instructions to associate the 3D coordinate system with the calibration target, wherein the 3D coordinate system comprises a vertical z-axis from the center of the calibration target, and a horizontal x-axis and horizontal y-axis along the surface of the calibration target;

determine a rotation and translation that brings the four corners of the second captured image into correspondence with the four corners of the calibration target; and

identify the internal corner points of the repetitive pattern in the second captured image, wherein creating the 3D calibration information comprises instructions to;

select at least one of the set of intrinsic calibration parameter value options based on a result of a comparison of the calibration target to the first captured image and the second captured image; and

calibrate a 3D coordinate system of at least one of the camera and the projector to the real world coordinate frame of the calibration target based on the selected intrinsic calibration parameter value, the rotation and translation, and the internal corner points.

12. The computer readable non-transitory storage medium of claim 11, wherein the calibration target comprises an input device associated with a computing system including the projector and the camera.

13. The computer readable non-transitory storage medium of claim 11, further comprising instructions to select at least one of the calibration intrinsic parameter value options based on a residual error associated with the intrinsic parameter value.

14. The computer readable non-transitory storage medium of claim 11, wherein the intrinsic parameter value options comprise intrinsic parameter values associated with other devices.