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CSCE 641 Computer Graphics: Image Mosaicing

CSCE 641 Computer Graphics: Image Mosaicing. Jinxiang Chai. Outline. Image registration - How to break assumptions? 3D-2D registration Image mosaicing. virtual wide-angle camera. Mosaics: Stitching Image Together. Mosaic Procedure. Basic Procedure. Mosaic Procedure. Basic Procedure

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CSCE 641 Computer Graphics: Image Mosaicing

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  1. CSCE 641 Computer Graphics: Image Mosaicing Jinxiang Chai

  2. Outline Image registration - How to break assumptions? 3D-2D registration Image mosaicing

  3. virtual wide-angle camera Mosaics: Stitching Image Together

  4. Mosaic Procedure Basic Procedure

  5. Mosaic Procedure Basic Procedure • Take a sequence of images from the same position • Rotate the camera about its optical center

  6. Mosaic Procedure Basic Procedure • Take a sequence of images from the same position • Rotate the camera about its optical center • Compute transformation between second image and first

  7. Mosaic Procedure Basic Procedure • Take a sequence of images from the same position • Rotate the camera about its optical center • Compute transformation between second image and first • Transform the second image to overlap with the first

  8. Mosaic Procedure Basic Procedure • Take a sequence of images from the same position • Rotate the camera about its optical center • Compute transformation between second image and first • Transform the second image to overlap with the first • Blend the two together to create a mosaic

  9. Mosaic Procedure Basic Procedure • Take a sequence of images from the same position • Rotate the camera about its optical center • Compute transformation between second image and first • Transform the second image to overlap with the first • Blend the two together to create a mosaic • If there are more images, repeat

  10. real camera synthetic camera Image Mosaic Is a pencil of rays contains all views Can generate any synthetic camera view as long as it has the same center of projection!

  11. mosaic PP Image Re-projection The mosaic has a natural interpretation in 3D • The images are reprojected onto a common plane • The mosaic is formed on this plane • Mosaic is a synthetic wide-angle camera

  12. Issues in Image Mosaic How to relate two images from the same camera center? - image registration How to re-project images to a common plane? - image warping ? ? mosaic PP

  13. Image Mosaicing Geometric relationship between images

  14. Image Mosaicing Geometric relationship between images • Use 8-parameter projective transformation matrix

  15. Image Mosaicing Geometric relationship between images • Use 8-parameter projective transformation matrix • Use a 3D rotation model (one R per image) Derive it by yourself!

  16. Image Mosaicing Geometric relationship between images • Use 8-parameter projective transformation matrix • Use a 3D rotation model (one R per image) Register all pairwise overlapping images • Feature-based registration • Pixel-based registration Chain together inter-frame rotations

  17. Image Stitching Stitch pairs together, blend, then crop

  18. Image Stitching A big image stitched from 5 small images

  19. mosaic Projection Cylinder Panoramas What if you want a 360 field of view?

  20. Cylindrical Panoramas Steps • Re-project each image onto a cylinder • Blend • Output the resulting mosaic

  21. Y X Z Cylindrical Projection • Map 3D point (X,Y,Z) onto cylinder unit cylinder

  22. Y • Convert to cylindrical coordinates X Z unwrapped cylinder Cylindrical Projection • Map 3D point (X,Y,Z) onto cylinder unit cylinder

  23. Y • Convert to cylindrical coordinates X Z unwrapped cylinder cylindrical image Cylindrical Projection • Map 3D point (X,Y,Z) onto cylinder • Convert to cylindrical image coordinates unit cylinder • s defines size of the final image

  24. Cylindrical Panoramas A B mosaic Projection Cylinder Cannot map point A to Point B without knowing (X,Y,Z)

  25. Cylindrical Panoramas A B C mosaic Projection Cylinder But we can map point C (images) to Point B.

  26. Given focal length f and image center (xc,yc) (X,Y,Z) (sinq,h,cosq) Y Z X Cylindrical Warping

  27. f = 180 (pixels) Image 384x300 f = 380 f = 280 Cylindrical Panoramas Map image to cylindrical or spherical coordinates • need known focal length

  28. Cylindrical Panorama 3D rotation registration of four images taken with a handheld camera.

  29. Cylindrical Panorama

  30. Recognizing panoramas • A fully automatic 2D image stitcher system Input Images Output panorama #1

  31. Recognizing panoramas • A fully automatic 2D image stitcher system Input Images Output panorama #2

  32. Recognizing panoramas • A fully automatic 2D image stitcher system Input Images Output panorama #3

  33. Recognizing panoramas • A fully automatic 2D image stitcher system Input Images - How to recognize which images can be used for panoramas? - How to stitch them automatically?

  34. Recognizing panoramas • A fully automatic 2D image stitcher system

  35. Recognizing panoramas • A fully automatic 2D image stitcher system • Image matching with SIFT features • For every image, find the M best images with RANSAC • form a graph and find connected component in the graph • Stitching and blending.

  36. Outline Image registration - How to break assumptions? (cont.) 3D-2D registration Image mosaicing

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