Fast Paint Texture

Aaron HertzmannNew York University

Pierce Groover

CS 395 – NPR

Thursday, January 22, 2004

Overview

• Texture plays important part in visual appearance

• Methods can take a long time• Let’s build faster/easy algorithm to

work with existing programs and hardware

Overview

Other work

• Simulated buildup of material– Cockshott et al. ’92, Curtis et al. 97– Processing time, fluid dynamics

• Fixed texture maps– Bronskill, Litwinowicz, Meier,

Markosian– No paint mixing or building– No consistent lighting on individual

strokes

Implementation - Overview

• Raw color image (brush strokes)• Height field is computed

– Height of the painted surface at each pixel

• Final painting generated by bump-mapping the raw image (Phong shading)

Brush Strokes

• Hertzmann and Perlin 2000– Could be any type of stroke though

• Brush stroke specified by a smooth curve – brush radius – solid color.– texture mapped

• Brush strokes are tesselated as triangle strips

Brush Strokes

Opacity Map

Base Image

• Render a color image– Paint color for each

pixel, without lighting

• Composite every brush stroke in back-to-front order– Use opacity map and

paint color

Height Map

• Per-pixel height of the painted surface.• Initialized to black (zero height)• Height determined by texture map, then…

– First strokes are drawn very dark, later strokes drawn lighter.

– Boundaries between the two appear as height discontinuities

• Note that the height map is not cumulative. – Adding stroke heights difficult to prevent

hidden strokes

Height Map

Texture MapHeight Field

Lighting

• Bump-map original flat image using directional derivatives from height map– Phong shading

• Done!

Results

Results

Results

Results

Future Work

• New types of stroke textures and new lighting functions

• Hardware vertex shaders

• Paint textures have the shiny, static appearance of viscous oil paint – More styles could probably be achieved with

suitable stroke textures, height and opacity textures.

Thank You

Questions?