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Introduction To IBR

Introduction To IBR. Ying Wu. View Morphing. Seitz & Dyer SIGGRAPH’96 Synthesize images in transition of two views based on two images No 3D shape is required. The Task. Image Morphing. A morph is determined from two images I 0 and I 1 and maps C 0 : I 0  I 1 and C 1 : I 1  I 0

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Introduction To IBR

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  1. Introduction To IBR Ying Wu

  2. View Morphing • Seitz & Dyer SIGGRAPH’96 • Synthesize images in transition of two views based on two images • No 3D shape is required

  3. The Task

  4. Image Morphing • A morph is determined from two images I0 and I1 and maps C0 : I0I1and C1: I1I0 • A warp function • W0and W1give the displacement of each point p0I0and p1I1 as a function of s[0; 1]. • The in-between images Isare computed by warping the two original images and averaging the pixel colors of the warped images.

  5. Problems for image morphing • Linearly interpolating two perspective views of a clock (far left and far right) causes a geometric bending effect in the in-between images. • The dashed line shows the linear path of one feature during the course of the transformation. • This example is indicative of the types of distortions that can arise with image morphing techniques.

  6. Notations

  7. Assumptions • Two images I1 and I2 of the same 3D objects • Their projection matrices 1 and 2 • Pixel correspondences of the two images

  8. Morphing Parallel Views

  9. Parallel views • Suppose the camera is moved from the world origin to position (Cx,Cy,0) and the focal length changes from f0 to f1, we have • If p0I0and p1I1 be projections of P=[X,Y,Z,1]T

  10. Shape preserving • So, what about non-parallel views?

  11. Image Reprojection • The 3x3 matrix is a projective transformation that reprojects the image plane of onto that of • The operation of reprojection is very powerful because it allows allows the gaze direction to be modified after a photograph is taken

  12. Non-parallel views

  13. Choose the world • Let I0 and I1 be two perspective views with projection matrices and • Choose the world coordinate system so that C0 and C1 lie on the world X-axis, i.e, • Choose the Y axis to be in the direction of the cross product of the two image plane normals

  14. Three-step algorithm

  15. Discussion • Can you see the relation of the prewarp step and the stereo rectification that we have learnt before?

  16. Exceptions: Singular views In the parallel configuration, each camera’s optical center is out of the field of view of the other. A singular configuration arises when the optical center of camera B is in the field of view of camera A. Because prewarping does not change the field of view, singular views cannot be reprojected to form parallel views.

  17. The procedure

  18. Examples

  19. More examples

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