Download - Poisson Image Editing - CGL @ ETHZCGL slideset 1 Poisson Image Editing Patric Perez, Michel Gangnet, and Andrew Black (SIGGRAPH 2003) Seminar Talk by Tim Weyrich CGL slideset 15 Mixing

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Page 1: Poisson Image Editing - CGL @ ETHZCGL slideset 1 Poisson Image Editing Patric Perez, Michel Gangnet, and Andrew Black (SIGGRAPH 2003) Seminar Talk by Tim Weyrich CGL slideset 15 Mixing

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Poisson Image Editing

Patric Perez, Michel Gangnet, and Andrew Black (SIGGRAPH 2003)

Seminar Talk by

Tim Weyrich

Page 2: Poisson Image Editing - CGL @ ETHZCGL slideset 1 Poisson Image Editing Patric Perez, Michel Gangnet, and Andrew Black (SIGGRAPH 2003) Seminar Talk by Tim Weyrich CGL slideset 15 Mixing

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Overview

• Guided Image Interpolation• Discretized Solution• Editing Operations• Discussion

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Interpolation Problem

• f *: known image values• f : unknown values over region Ω• Assuming scalar image values

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Simple Interpolation

• Maximize smoothness

• Boundary constraints

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Simple Interpolation

• Solution: Laplace Equation with Dirichletboundary conditions

• Membrane solution• Unsatisfactory due to over-blurring

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Guided Interpolation

• v: guided field• v may be gradient of a function g

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Guided Interpolation

• Minimize differenceof gradient fields

• Solution: Poisson Equationwith Dirichlet boundary conditions

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Discrete Poisson Solver• Discretize directly by

for neighbors p and q with

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Discrete Poisson Solver• Minimum satisfies linear system of equations

If neighborhood overlaps boundary:

For interior points:

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Discrete Poisson Solver

• Linear system of equations– sparse (banded)– symmetric– positive-definite

• Irregular shape of boundary requires general solver, such as– Gauss-Seidel iteration– Multi-grid

• System can be solved at interactive rates

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Seamless Cloning

• Importing Gradients froma Source Image g

• Discretize

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Seamless Cloning Results

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Page 14: Poisson Image Editing - CGL @ ETHZCGL slideset 1 Poisson Image Editing Patric Perez, Michel Gangnet, and Andrew Black (SIGGRAPH 2003) Seminar Talk by Tim Weyrich CGL slideset 15 Mixing

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Mixing Gradients• Two Variants

– v averaged from source and destination gradients transparency

– Select stronger one from source and destination gradients:

Discretization:

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Mixing Gradients Results

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Mixing Gradients Results

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Mixing Gradients Results

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Texture Flattening

• Preserve only salient gradients

with masking function so that

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Texture Flattening

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Local Illumination Changes

• Approximate tone mapping transformation after Fattal et al. 2002:

• Attenuating large gradients

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Local Color Changes

• Mix two differently colored version of original image– One provides f * outside– One provides g inside

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Local Color Changes

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Seamless Tiling• Select original image as g• Boundary condition:

– f *north = f *south = 0.5 (gnorth + gsouth)– Similarly for the east and west

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Discussion

Pros• Very general framework• No parameter tuning required• Method does not require precise selection• Versatile method

– Seamless cloning, mixing gradients– Texture flatening– Local changes of illumination and color– Seamless tiling

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Discussion

Cons• Cloning requires either of the images to be

smooth• No refined selection is returned• Minimization only adapts low-frequency

content– Potential color shift / re-coloring difficult to control– Dissatisfactory tiling– Cloning requires careful placement of prominent

features

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Outlook

• More image editing operators– Combinations (insert while flattening)– Other non-linear operations on gradients– More than one source images

• Poisson editing of triangle meshes– Feature transfer– Detail preserving deformations

• Other editing domains possible?

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Thanks

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Seamless Tiling

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Mixing Gradients Results