Non-Photorealistic Rendering

Non-PhotorealisticRendering

Greg TurkCollege of Computing and GVU Center

Painterly Rendering for Animation Barbara Meier, SIGGRAPH 1996

Painterly Rendering Issues

• Frame-to-frame coherence (maintain strokes across time)

• Idea: fix brush strokes in screen-space

• Problem: shower door effect

• Better idea: fix brush strokes to object

Painting Pipeline

Brushes (color & opacity):

Different Brushes and Orientation Fields

Draw Image in Layers

Video

Pen and Ink SketchesMike Salisbury, Michael Wong, John Hughesand David Salesin, SIGGRAPH 1997

Pen and Ink

• Given: grayscale image (e.g. photo)

• Make: pen-and-ink illustration

• Approach:

Gray scaleimage

Directionfield

BrushStrokes

FinalImage+ + =

Pen and Ink Sketches

ToneMap

OrientationField

Strokes

Pen and Ink Sketches

ToneMap

OrientationField

Strokes

Stroke Details

• Strokes are B-spline curves (similar to Bezier)

• Strokes clipped to silhouettes

• Stroke density controlled by blurred stroke image

• Strokes follow orientation field

Painting Orientation Field

Stroke Density

Strokes

BlurredStrokes

Stroke Density Varies with Drawing Size

Art-Based RenderingOf Fur, Grass andTrees

Kowalski, Markosian,Northrup, Bourdev,Barzel and Hughes,SIGGRAPH 2000

Approach

• Real-time rendering

• Use reference images for color and object ID

• Place “strokes” based on density

• Try to place same strokes on next frame

Reference Images: Hardware Rendering

Final Image

Stroke Drawing

“Illustrating Smooth Surfaces”Aaron Hertzmanand Denis ZorinSIGGRAPH 2000

Goals

• Create pen-and-ink strokes based on 3D geometry

• Show silhouettes

• Have cross-hatching

Issues

• Silhouette detection

• Orientation field (use curvature)

• Hatching

• Undercuts

Silhouette Detection

Orientation Field Smoothing

Orientation Field and Shading

Hatching

Hatching and Undercuts

Results

Results

Other NPR

• Cel Animation

• Painterly Video

• Cel Video

• ???

Painterly Video

“What Dreams May Come”

Cel Animation: Zelda Windwalker

Cel-Like Video

End