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 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.

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 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

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.