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# How to do it?

• 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

• but wait, why should this work at all?

• What about the 3D geometry of the scene?

• Why aren’t we using it?

# Aligning images: translation

left on top

right on top

Translations are not enough to align the images

# Image reprojection

• Basic question

• How to relate 2 images from same camera center?

• how to map a pixel from PP1 to PP2

• Cast a ray through each pixel in PP1

• Draw the pixel where that ray intersects PP2

But don’t we need to know the geometry of the two planes in respect to the eye?

PP1

PP2

Observation: Rather than thinking of this as a 3D reprojection, think of it as a 2D image warp from one image to another

real

synthetic

camera

camera

# A pencil of rays contains all views

Can generate any synthetic camera view as long as it has the same center of projection!

# Image reprojection

mosaic PP

• 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

# Back to Image Warping

Which t-form is the right one for warping PP1 into PP2? e.g. translation, Euclidean, affine, projective

## Perspective

2 unknowns

6 unknowns

8 unknowns

2

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