Animosaics

AnimosaicsKaleigh 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

Introduction Arrange and rearrange small objects or tiles from fram

e to frame. Manually placing and moving pieces is time-consumin

g. 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 shape

s using area-based centrodial Voronoi diagram.

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 pa

cking. Both the tiles and containers can be arbitrary shape

d.

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.

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.

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 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.

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


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.


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.


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 tohappen only at the boundary.

Preserve a packing’s interiororganization.

The system automatically choosesthe anchor point with thesmallest displacement betweentwo frames.

The animator can choose ifdesired.

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.

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 sh

apes.

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.

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.

Animosaics

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