Method and system for alignment of a pattern on a spatial coded slide image

• US 8,836,766 B1
• Filed: 11/02/2012
• Issued: 09/16/2014
• Est. Priority Date: 11/23/2011
• Status: Active Grant

• Current Assignee: Creaform, Inc. (Ametek Incorporated)
• Original Assignee: Creaform, Inc. (Ametek Incorporated)
• Inventors: Hebert, Patrick, Rochette, Flix
• Primary Examiner(s): Senfi, Behrooz
• Assistant Examiner(s): Jebari, Mohammed
• Application Number:
  US13/699,773
• Publication Number:
  US 20140247326A1
• Time in Patent Office: 683 Days
• Field of Search: None
• US Class Current: 348/46
• CPC Class Codes: G01B 11/2504 Calibration devices
• CPC Class Codes: G01B 11/2513 with several lines being projected in more than one direction, e.g. grids, patterns
• CPC Class Codes: G06T 5/80 Geometric correction
• CPC Class Codes: G06T 7/521 from laser ranging, e.g. using interferometry; from the projection of structured light
• CPC Class Codes: H04N 13/275 from 3D object models, e.g. computer-generated stereoscopic image signals

Abstract

A method for preparing a spatial coded slide image in which a pattern of the spatial coded slide image is aligned along epipolar lines at an output of a projector in a system for 3D measurement, comprising: obtaining distortion vectors for projector coordinates, each vector representing a distortion from predicted coordinates caused by the projector; retrieving an ideal pattern image which is an ideal image of the spatial coded pattern aligned on ideal epipolar lines; creating a real slide image by, for each real pixel coordinates of the real slide image, retrieving a current distortion vector; removing distortion from the real pixel coordinates using the current distortion vector to obtain ideal pixel coordinates in the ideal pattern image; extracting a pixel value at the ideal pixel coordinates in the ideal pattern image; copying the pixel value at the real pixel coordinates in the real slide image.

Claims

1. A method for preparing a spatial coded slide image in which a pattern of said spatial coded slide image is aligned along epipolar lines at an output of a projector in a system for 3D measurement of a shape of an object, having the projector and a camera in full-field structured light, comprising:

obtaining a set of distortion vectors for projector coordinates of said projector, each said distortion vector representing a distortion from predicted coordinates caused by said projector;

retrieving an ideal pattern image, wherein said ideal pattern image is an ideal image of the spatial coded pattern aligned on ideal epipolar lines;

creating a real slide image by, for each real pixel coordinates of the real slide image,

retrieving a current distortion vector from said set using said real pixel coordinates;

removing distortion from said real pixel coordinates using the current distortion vector to obtain ideal pixel coordinates in the ideal pattern image;

extracting a pixel value at the ideal pixel coordinates in the ideal pattern image;

copying the pixel value at the real pixel coordinates in the real slide image.

2. The method as claimed in claim 1, wherein said creating a real slide image includes creating an electronic version of said real slide image and providing said electronic version to a programmable projector.

3. The method as claimed in claim 1, wherein said extracting a pixel value includes interpolating said pixel value.

4. The method as claimed in claim 1, wherein said pixel value is a level value.

7. A method for setting up a system for 3D measurement of a shape of an object, having a projector with a fixed slide mask and a camera in full-field structured light, comprising:

setting the lens aperture and focus;

carrying the steps of claim 1;

mounting said slide rigidly with the projector lens and aligning a center of said slide with an optical axis of the lens;

adjusting rotation around the optical axis of the lens and the translation of the projector along the optical axis of the lens so as to align the pattern code along the epipolar lines.

5. A method for facilitating matching of coded patterns between a projected image and a captured image in a system for 3D measurement of a shape of an object, having a projector and a camera in full-field structured light, comprising:

calibrating the projector and the camera for intrinsic and extrinsic parameters;

preparing a spatial coded slide image in which a pattern of said spatial coded slide image is aligned along epipolar lines by

obtaining a set of distortion vectors for projector coordinates of said projector, each said distortion vector representing a distortion from predicted coordinates caused by said projector;

retrieving an ideal pattern image, wherein said ideal pattern image is an ideal image of the spatial coded pattern aligned on ideal epipolar lines;

creating a real slide image by, for each real pixel coordinates of the real slide image,

retrieving a current distortion vector from said set using said real pixel coordinates;

removing distortion from said real pixel coordinates using the current distortion vector to obtain ideal pixel coordinates in the ideal pattern image;

extracting a pixel value at the ideal pixel coordinates in the ideal pattern image;

copying the pixel value at the real pixel coordinates in the real slide image;

projecting the spatial coded pattern on a scene object using the projector;

observing the spatial coded pattern on the object using the camera to generate a camera image;

processing the camera image to match codes with the projected image.

6. The method as claimed in claim 5, further comprising undistorting and rectifying the camera image prior to said processing the camera image.