Fixed pattern calibration for multi-view stitching

1. An apparatus comprising:

an interface configured to receive pixel data from two or more cameras arranged to obtain a predetermined field of view, wherein respective fields of view of each pair of said two or more cameras overlap; and

a processor configured to process said pixel data arranged as video frames and perform a fixed pattern calibration for facilitating multi-view stitching, said fixed pattern calibration comprising (a) performing a geometry calibration process to obtain intrinsic parameters and distortion parameters for each lens of said two or more cameras, and (b) applying a pose calibration process to said video frames, wherein said pose calibration process uses (i) said intrinsic parameters, a respective translate vector, a respective rotation matrix, and said distortion parameters for each lens of said two or more cameras and (ii) a calibration board to obtain configuration parameters for the respective fields of view of said two or more cameras, and said pose calibration process comprises changing a z value of said respective translate vector for each lens of said two or more cameras to at least one of a middle distance value and a long distance value while maintaining said respective rotation matrix for each lens of said two or more cameras unchanged.

2. The apparatus according to claim 1 , wherein said pose calibration process comprises using at least one of a circle detector and a chessboard detector to detect a circle center or a corner, respectively, on the calibration board; and

determining whether a detected point in one view is matched in another view.

3. The apparatus according to claim 1 , wherein said pose calibration process further comprises performing an extrinsic calibration for each lens of said two or more cameras using said intrinsic parameters and said distortion parameters for each lens of said two or more cameras, wherein extrinsic parameters for each lens of said two or more cameras comprise said respective rotation matrix and said respective translate vector.

4. The apparatus according to claim 1 , wherein said pose calibration process comprises projecting key points from world coordinates to image coordinates.

5. The apparatus according to claim 1 , wherein said pose calibration process comprises calculating a respective homography matrix between each adjacent pair of said two or more cameras.

6. The apparatus according to claim 5 , wherein said respective homography matrix between each adjacent pair of said two or more cameras is based on a center view.

7. The apparatus according to claim 5 , wherein said pose calibration process comprises:

applying said intrinsic parameters and said distortion parameters for each lens of said two or more cameras to a corresponding image; and

warping the corresponding image with the respective homography matrix.

8. The apparatus according to claim 1 , wherein said pose calibration process comprises applying a projection model to views of said two or more cameras.

9. The apparatus according to claim 8 , wherein:

for horizontal direction stitching said projection model comprises at least one of a perspective model, a cylindrical model, and an equirectangular model; and

for vertical direction stitching said projection model comprises at least one of a transverse cylindrical model and a mercator model.

10. A method of fixed pattern calibration for multi-view stitching with multiple cameras comprising:

arranging two or more cameras to obtain a predetermined field of view, wherein respective fields of view of each adjacent pair of said two or more cameras overlap;

performing a geometry calibration process to obtain intrinsic parameters and distortion parameters for each lens of said two or more cameras; and

applying a pose calibration process to video frames from said two or more cameras, wherein said pose calibration process uses (i) said intrinsic parameters, a respective translate vector, a respective rotation matrix, and said distortion parameters for each lens of said two or more cameras and (ii) a calibration board to obtain configuration parameters for the respective fields of view of said two or more cameras, and said pose calibration process comprises changing a z value of said respective translate vector for each lens of said two or more cameras to at least one of a middle distance value and a long distance value while maintaining said respective rotation matrix for each lens of said two or more cameras unchanged.

11. The method according to claim 10 , wherein said pose calibration process comprises using at least one of a circle detector and a chessboard detector to detect a circle center or a corner, respectively, on the calibration board; and

determining whether a detected point in one view is matched in another view.

12. The method according to claim 10 , wherein said pose calibration process further comprises performing an extrinsic calibration for each lens of said two or more cameras using said intrinsic parameters and said distortion parameters for each lens of said two or more cameras, wherein extrinsic parameters for each lens of said two or more cameras comprise said respective rotation matrix and said respective translate vector.

13. The method according to claim 10 , wherein said pose calibration process comprises projecting key points from world coordinates to image coordinates.

14. The method according to claim 10 , wherein said pose calibration process comprises calculating a respective homography matrix between each adjacent pair of said two or more cameras.

15. The method according to claim 14 , wherein said respective homography matrix between each adjacent pair of said two or more cameras is based on a center view.

16. The method according to claim 14 , wherein said pose calibration process comprises:

applying said intrinsic parameters and said distortion parameters for each lens of said two or more cameras to a corresponding image; and

warping the corresponding image with the respective homography matrix.

17. The method according to claim 10 , wherein said pose calibration process comprises applying a projection model to views of said two or more cameras.

18. The method according to claim 17 , wherein:

for horizontal direction stitching said projection model comprises at least one of a perspective model, a cylindrical model, and an equirectangular model; and

for vertical direction stitching said projection model comprises at least one of a transverse cylindrical model and a mercator model.

19. The method according to claim 17 , wherein said pose calibration process comprises cropping each view to an inscribed quadrilateral, while maintaining an aspect ratio of the quadrilateral, and zooming to an original size of each view.

20. The method according to claim 10 , wherein said configuration parameters are obtained for one or more of an offset, a width, and a height of the respective fields of view of said two or more cameras.