Image and View MorphingImage and View Morphing

[Beier and Neely ’92, Chen and Williams ’93, Seitz and Dyer ’96]

OverviewOverview

Image morphing can look interesting, but morphs don’t usually account for differences in viewpoint

“shape-preserving” means that each in-between image looks like the same object, but in a different orientation, position, etc.

Most morphs are not shape-preserving, especially if the viewpoint or object orientation changes

View morphing is an extension to image morphing that handles 3D projection, scene transformations, and changes in viewpoint

Existing Morphing Techniques DistortExisting Morphing Techniques Distort

Image-morphing is a class of techniques for producing transitions between images Recall Beier-Neely

Does morphing preserve shape? Do all the in-between images look real? If “Yes”, then the morph is shape-preserving

In general, morphs are not shape-preserving

View morphing tries to produce shape-preserving morphs

Existing Morphing Techniques DistortExisting Morphing Techniques Distort

Linear interpolation between two perspective views

of a clock face.[1]

View MorphingView Morphing

The view morphing technique has three steps: Pre-warp of source and destination images Morph using some existing technique, such as Beier-Neely Post-warp to get interpolated image (in-between image)

View morphing requires: Two images Information about the projections

View Morphing DemoView Morphing Demo

[2]

Symbol GlossarySymbol Glossary

center optical

scamera' thespecifiesat vector th1 x 3 a is C

scoordinate in worldn orientatio plane image

thespecifies ation that transform3 x 3 a is

matrix projection 4 x 3 a is

imagebetween -inan is

image end theis image,start theis 10

H

HCHΠ

Π

I

II

s

View Morphing with Parallel ViewsView Morphing with Parallel Views

Suppose we have two images of the same scene where the viewpoint is translated parallel to the view plane

This is already shape-preserving

Seitz and Dyer offer a proof

But what about non-parallel views?

Image ReprojectionImage Reprojection

We can use image reprojection to change the gaze direction of an existing image

Assumes that the camera’s optical center doesn’t move

Reprojection can be done efficiently with an algorithm due to Wolberg [3].

Image Reprojection FormulaeImage Reprojection Formulae

Ip

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CHHΠ-HCH Π ˆˆ and

are matrices projection ingcorrespond The

pHHp

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1

View Morphing with Non-Parallel ViewsView Morphing with Non-Parallel Views

Image reprojection can be used to make two new images where the views are parallel

Parallel view morphing can be used to generate in-between images in this parallel space

A post-warp stage is added to get the real in-between image

View Morphing with Non-Parallel ViewsView Morphing with Non-Parallel Views

[1]

View Morphing with Non-Parallel ViewsView Morphing with Non-Parallel Views

I0 and I1 are endpoint images

Recall that Hs is the matrix that describes the placement of the image plane in space.

Morph is done in three steps Apply H0

-1 to I0 and H1-1 to I1

Morph using parallel view technique (e.g. Beier-Neely or linear interpolation)

Apply Hs to in-between image from previous step

View Morphing with Non-Parallel ViewsView Morphing with Non-Parallel Views

How do we pick Hs ? Interpolate an angle of rotation, which can be determined from the

normals of the image view planes or Hs can be determined by interactively selecting four non-collinear

corresponding points before and after the post-warp step at s = 0.5.

Does it work?Does it work?

Yes...

... but there are limitations Blurriness Relies on other morphing technique as an intermediate step, so we’re

also stuck with the limitations of the selected morphing technique (e.g. holes)

More View Morphing DemosMore View Morphing Demos

[2]

SummarySummary

View morphing: Does a morph between two images where the viewpoint has changed Can produce a realistic looking transition Uses some other morphing technique as an intermediate step Uses two pre-warps and a post-warp

References, AcknowledgementsReferences, Acknowledgements

[1] Seitz, Steven and Charles Dyer. View Morphing. Proceedings of SIGGRAPH 96

[2] Movies are all from Steven Seitz’s view morphing web site: http://www.cs.washington.edu/homes/seitz/vmorph/vmorph.htm

[3] Wolberg, George. Digital Image Warping. IEEE Computer Society Press, Los Alamitos, CA, 1990. Unfortunately out of print.