Transcript Animosaics Eurographics Symposium on Computer Animation 2005

Animosaics
Kaleigh Smith, Yunjun Liu, and Allison Klein
McGill University
Eurographics Symposium on
Computer Animation 2005
Abstract
Animated mosaics are a traditional form of
stop-motion animation.
 It is time-consuming and labourious.

Outline
Introduction
 Related Work
 Temporal Coherence and Group Motion
 Construction of a Mosaic Animation
 System Details
 Results
 Conclusion and Future Work

Outline
Introduction
 Related Work
 Temporal Coherence and Group Motion
 Construction of a Mosaic Animation
 System Details
 Results
 Conclusion and Future Work

Introduction





Arrange and rearrange small objects or tiles from
frame to frame.
Manually placing and moving pieces is timeconsuming.
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.
Outline
Introduction
 Related Work
 Temporal Coherence and Group Motion
 Construction of a Mosaic Animation
 System Details
 Results
 Conclusion and Future Work

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.
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.
Outline
Introduction
 Related Work
 Temporal Coherence and Group Motion
 Construction of a Mosaic Animation
 System Details
 Results
 Conclusion and Future Work

Temporal Coherence and
Group 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.

Outline
Introduction
 Related Work
 Temporal Coherence and Group Motion
 Construction of a Mosaic Animation
 System Details
 Results
 Conclusion and Future Work

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
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
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 perframe 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.
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 container’s first frame.
Generate the remaining frames in two step:


1) The system automatically advects the container’s tile
from the current frame to the next
2) The animator optionally inserts new tiles and refines
the current packing to reflect container changes.
Construction of a Mosaic
Animation

Mosaic Packing



Tile Orientation
Tile Repositioning
Temporally Coherent Tile Movement
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.
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.
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
Construction of a Mosaic
Animation

Temporally Coherent Tile Movement
Construction of a Mosaic
Animation

Anchor-point mapping




Cause insertion or deletions to
happen only at the boundary.
Preserve a packing’s interior
organization.
The system automatically chooses
the anchor point with the
smallest displacement between
two frames.
The animator can choose if
desired.
Construction of a Mosaic
Animation

Nearest-edge mapping


Preserve the packing boundary
instead of the interior.
The interior tiles move away form
the center as a container increase.
Outline
Introduction
 Related Work
 Temporal Coherence and Group Motion
 Construction of a Mosaic Animation
 System Details
 Results
 Conclusion and Future Work

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.
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 container’s 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.
Outline
Introduction
 Related Work
 Temporal Coherence and Group Motion
 Construction of a Mosaic Animation
 System Details
 Results
 Conclusion and Future Work

Outline
Introduction
 Related Work
 Temporal Coherence and Group Motion
 Construction of a Mosaic Animation
 System Details
 Results
 Conclusion and Future Work

Result
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.
