Animosaics

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Animosaics

• Kaleigh Smith, Yunjun Liu, and Allison Klein
• McGill University

Eurographics Symposium on Computer Animation 2005
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Abstract

• Animated mosaics are a traditional form of
  stop-motion animation.
• It is time-consuming and labourious.

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Outline

• Introduction
• Related Work
• Temporal Coherence and Group Motion
• Construction of a Mosaic Animation
• System Details
• Results
• Conclusion and Future Work

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Outline

• Introduction
• Related Work
• Temporal Coherence and Group Motion
• Construction of a Mosaic Animation
• System Details
• Results
• Conclusion and Future Work

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Introduction

• Arrange and rearrange small objects or tiles from
  frame to frame.
• Manually placing and moving pieces is
  time-consuming.
• Making small changes means exactly
  reconstructing.
• Packing objects to fill a desired shape is a
  problem in computer science.
• Create static mosaics comprised of different tile
  shapes using area-based centrodial Voronoi
  diagram.

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Outline

• Introduction
• Related Work
• Temporal Coherence and Group Motion
• Construction of a Mosaic Animation
• System Details
• Results
• Conclusion and Future Work

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Related Work

• Simulating decorative mosaics.Hausner A. 01
• Take as input a rectangular image.
• Generate a mosaic composed of rectangular or oval
  tiles
• Discuss methods for tile orientation
• Jigsaw Image Mosaics. Kim Pellacini 02
• Define a metric that measures the quality of a
  tile packing.
• Both the tiles and containers can be arbitrary
  shaped.

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Related Work

• (a) packs a single tile shape well.
• (b) achieves tight packings with irregular
  shapes.
• The CAVD approach (c) handles any variety of
  arbitrary shapes.

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Outline

• Introduction
• Related Work
• Temporal Coherence and Group Motion
• Construction of a Mosaic Animation
• System Details
• Results
• Conclusion and Future Work

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Temporal Coherence andGroup Motion

• Minimize temporal discontinuities while having
  primitives appear attached to underlying scene
  object.
• Even if individual primitives have temporal
  smoothness, uncoordinated changes among groups of
  NPR primitives will still yield distracting.

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Outline

• Introduction
• Related Work
• Temporal Coherence and Group Motion
• Construction of a Mosaic Animation
• System Details
• Results
• Conclusion and Future Work

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Construction of a Mosaic Animation

• A temporally coherent sequence of mosaic images
  over time.
• Given a container C (a closed polygon over time)
  and a collection of tile shapes T (called a
  packing of C).
• Three challenges
• 1) Temporal coherence
• 2) Stylistic coherence
• 3) Performance

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Construction of a Mosaic Animation

• 1) Temporal coherence
• Tiles should move smoothly, appear attached to
  their underlying object
• Tile appearances or disappearances should be
  minimized
• 2) Stylistic coherence
• Tiles are evenly distributed, tightly packed with
  minimal overlaps,
• Tiles orientations reflect the edge of the
  container shape

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Construction of a Mosaic Animation

• 3) Performance
• In order to support input from the animator, the
  first two properties should be achieved as
  interactively as possible
• Conflict between these three goals
• Independently packing each frame will lead to
  high per-frame mosaic quality, but at the cost of
  distracting temporal artifacts.
• Very smooth, coherent tile movements may not
  yield pleasing individual mosaic.
• Performance requirements limit the amount of time
  that can be spent optimizing either for packing
  quality or temporal coherence.

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Construction of a Mosaic Animation

• Take as input an animated scene represented as a
  collection of 2D containers (polygons).
• Pick the desired tile shapes and sizes, then pack
  the containers first frame.
• Generate the remaining frames in two step
• 1) The system automatically advects the
  containers tile from the current frame to the
  next
• 2) The animator optionally inserts new tiles and
  refines the current packing to reflect container
  changes.

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Construction of a Mosaic Animation

• Mosaic Packing
• Tile Orientation
• Tile Repositioning
• Temporally Coherent Tile Movement

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Construction of a Mosaic Animation

• Mosaic Packing
• Tile Orientation
• Similar container shapes should lead to similar
  orientation fields.
• KP02 preserves container edges by fitting tiles
  against boundaries and previously placed tiles.
• Reinforce container edges but do not preserve an
  internal orientation field.
• Hau01 aligns tiles to a continuous orientation
  field based on feature lines.
• EW03 align tiles along concentric contour lines
  to emphasize container shape.

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Construction of a Mosaic Animation

• Mosaic Packing
• Tile Orientation
• Preserve the container shape boundary by aligning
  each tile with its closest container edge.
• To enable tighter packings and reduce image
  regularity, each tile shape may have a set of
  equivalent orientations.

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Construction of a Mosaic Animation

• Mosaic Packing
• Tile Repositioning
• Use an artist-specified collection of arbitrary
  tile shapes to pack a container.
• centroidal Voronoi diagram vs.
• centroidal area Voronoi diagram

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Construction of a Mosaic Animation

• Temporally Coherent Tile Movement

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Construction of a Mosaic Animation

• Anchor-point mapping
• Cause insertion or deletions tohappen only at
  the boundary.
• Preserve a packings interiororganization.
• The system automatically choosesthe anchor point
  with thesmallest displacement betweentwo
  frames.
• The animator can choose ifdesired.

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Construction of a Mosaic Animation

• Nearest-edge mapping
• Preserve the packing boundaryinstead of the
  interior.
• The interior tiles move away formthe center as a
  container increase.

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Outline

• Introduction
• Related Work
• Temporal Coherence and Group Motion
• Construction of a Mosaic Animation
• System Details
• Results
• Conclusion and Future Work

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System Details

• Container Specification
• Containers are specified as scalable vector
  graphics (SVG) animation.
• SVG is a human-readable format for describing 2D
  graphics shapes in XML and enables easy
  specification of vector graphic shapes and
  animations.
• Use a graphic SVG editor (Corel WebDraw).
• Translate scene elements into colored container
  shapes.

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System Details

• Packing
• The artist choose the set of shapes and the
  number of tiles.
• The system calculate the tiles size for each
  shape to randomly seed in the container.
• Each tile is assigned its containers color.
• Tiles can be add manually or automatically.
• The artist can also add noise to tile positions
  and orientation for a more hand-crafted look.

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Outline

• Introduction
• Related Work
• Temporal Coherence and Group Motion
• Construction of a Mosaic Animation
• System Details
• Results
• Conclusion and Future Work

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Outline

• Introduction
• Related Work
• Temporal Coherence and Group Motion
• Construction of a Mosaic Animation
• System Details
• Results
• Conclusion and Future Work

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Result
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Conclusion and Future Work

• Meets the three challenges of temporal coherence,
  per-frame mosaic quality, and performance that
  supports interactive input from the artist.
• Use area-based centroidal Voronoi diagrams to
  create mosaics comprised of different tile
  shapes.
• Blend in other NPR animation styles.
• Pack 3D volumes with 3D objects.