Non-Photorealistic Photorealistic Rendering Rendering Non- - - PowerPoint PPT Presentation

Non- Non-Photorealistic Photorealistic Rendering Rendering

Pen-and-Ink Illustration Pen-and-Ink Illustration

Stylized Illustrations Stylized Illustrations

As compared to As compared to photorealistic photorealistic images, images, sometimes: sometimes:

• Convey more information

Convey more information

• Allow more compact storage

Allow more compact storage

• More easily reproduced

More easily reproduced

• More attractive

More attractive

Illustration Applications Illustration Applications

Architectural design Architectural design Medical texts Medical texts Industrial repair manuals Industrial repair manuals

Types of Types of Non- Non-Photorealistic Photorealistic Rendering Rendering

Pen-and-ink Drawings Pen-and-ink Drawings Paintings Paintings Rendering enhancements Rendering enhancements Other artistic modalities Other artistic modalities

• e.g. screening, floral ornamentation,

e.g. screening, floral ornamentation, cartoons, etc. cartoons, etc.

Pen and Ink Concepts Pen and Ink Concepts

Strokes Strokes

• Curved lines of varying thickness and

Curved lines of varying thickness and density of placement density of placement

Texture Texture

• Character conveyed by collection of strokes,

Character conveyed by collection of strokes, e.g. crisp and clean e.g. crisp and clean vs

• vs. rough and sketchy

. rough and sketchy

Tone Tone

• Perceived gray level across the image

Perceived gray level across the image

Outline Outline

• Boundary lines which disambiguate

Boundary lines which disambiguate structure information structure information

Algorithm Goal Algorithm Goal

Place strokes on surfaces to achieve Place strokes on surfaces to achieve particular tone functions particular tone functions

from from Winkenbach Winkenbach and and Salesin

• Salesin. “Rendering

. “Rendering Parametric Surfaces in Pen Parametric Surfaces in Pen and Ink.” and Ink.” Proceedings of Proceedings of SIGGRAPH 96 SIGGRAPH 96. Page 471. . Page 471.

Algorithm Components Algorithm Components

Tone specification Tone specification Stroke placement Stroke placement Stroke width computation Stroke width computation

Tone Specification Tone Specification

Gray levels may be assigned according to Gray levels may be assigned according to conventional rendering: conventional rendering:

• Local/global Illumination

Local/global Illumination

• Material color

Material color

• Texture mapping

Texture mapping

• Bump mapping

Bump mapping

• Environment mapping

Environment mapping

• Shadow mapping

Shadow mapping

Stroke Placement Stroke Placement

Places strokes along Places strokes along isoparameter isoparameter lines of lines of parameterized surface parameterized surface Choose density according to maximum Choose density according to maximum gray level and maximum allowable stroke gray level and maximum allowable stroke width width

v u

Planar Maps Planar Maps

Compute visibility and store in planar map Compute visibility and store in planar map

• Planar map is partition of image plane

Planar map is partition of image plane

• Each partition corresponds to a visible

Each partition corresponds to a visible portion of a primitive (curved surfaces are portion of a primitive (curved surfaces are tessellated). tessellated).

• Shadows may be explicitly represented as

Shadows may be explicitly represented as map partitions map partitions

Clip strokes according to planar map Clip strokes according to planar map

• Reduces computation and allows rendering

Reduces computation and allows rendering with hidden surfaces already removed with hidden surfaces already removed

Create outlines from partition boundaries Create outlines from partition boundaries

Planar Map Example Planar Map Example

from from Winkenbach Winkenbach and and Salesin

• Salesin. “Rendering

. “Rendering Parametric Surfaces in Pen Parametric Surfaces in Pen and Ink.” and Ink.” Proceedings of Proceedings of SIGGRAPH 96 SIGGRAPH 96. Page 474. . Page 474.

Stroke Width Stroke Width

Vary width across each stroke line Vary width across each stroke line S: (u,v) S: (u,v) → → → → ( (x xw

w,

,y yw

w,

,z zw

w)

) V: ( V: (x xw

w,

,y yw

w,

,z zw

w)

) → → → → ( (x xs

s,

,y ys

s)

) M = V S : (u,v) M = V S : (u,v) → → → → ( (x xs

s,

,y ys

s)

) Use Use Jacobian Jacobian of M to estimate divergence

• f M to estimate divergence
• f lines in screen space
• f lines in screen space

Adjust width to account for divergence and Adjust width to account for divergence and desired tone along each stroke desired tone along each stroke

Advanced Techniques Advanced Techniques

Recursive filler strokes Recursive filler strokes

• Allow larger gaps between strokes, then fill

Allow larger gaps between strokes, then fill gaps by adding new strokes gaps by adding new strokes

Stippling Stippling

• draw stipple pattern along strokes

draw stipple pattern along strokes

Cross hatching Cross hatching

• use more than one hatching direction

use more than one hatching direction

Prioritized strokes Prioritized strokes

• stroke

stroke thicknesses thicknesses determined in prioritized determined in prioritized

• rder
• rder

Pen and Ink Example Pen and Ink Example

from from Winkenbach Winkenbach and and Salesin

• Salesin. “Rendering

. “Rendering Parametric Surfaces in Pen Parametric Surfaces in Pen and Ink.” and Ink.” Proceedings of Proceedings of SIGGRAPH 96 SIGGRAPH 96. Page 474. . Page 474.

Pen and Ink Example Pen and Ink Example

from from Winkenbach Winkenbach and and Salesin

• Salesin. “Rendering

. “Rendering Parametric Surfaces in Pen Parametric Surfaces in Pen and Ink.” and Ink.” Proceedings of Proceedings of SIGGRAPH 96 SIGGRAPH 96. Page 475. . Page 475.

Pen and Ink Example Pen and Ink Example

from from Winkenbach Winkenbach and and Salesin

• Salesin. “Rendering Parametric Surfaces

. “Rendering Parametric Surfaces in Pen and Ink.” in Pen and Ink.” Proceedings of SIGGRAPH 96 Proceedings of SIGGRAPH 96. Page 476. . Page 476.

Other Variants of Pen and Ink Other Variants of Pen and Ink

Orientable Orientable Textures Textures

• Greyscale

Greyscale image as input (describes tone) image as input (describes tone)

• User specifies direction field and stroke

User specifies direction field and stroke character character

• Stroke shaded image output

Stroke shaded image output

Real-time NPR Real-time NPR

• Fast visibility computation of silhouette and

Fast visibility computation of silhouette and

• ther feature edges
• ther feature edges
• Render visible edges in modified styles

Render visible edges in modified styles

Orientable Orientable Textures Examples Textures Examples

from from Salissbury Salissbury et al. “ et al. “Orientable Orientable Textures for Textures for Imabe Imabe-Based

• Based

Pen-and-Ink Illustration.” Pen-and-Ink Illustration.” Proceedings of SIGGRAPH 97 Proceedings of SIGGRAPH 97. Pages . Pages 402, 403. 402, 403.

Real-Time NPR Examples Real-Time NPR Examples

from from Markosian Markosian et al. “Real-Time et al. “Real-Time Nonphotorealistic Nonphotorealistic Rendering.” Rendering.” Proceedings Proceedings

• f SIGGRAPH 97
• f SIGGRAPH 97. Page 420.

. Page 420.

Videos Videos

• Salisbury, Wong, Hughes, and

Salisbury, Wong, Hughes, and Salesin Salesin. . “ “Orientable Orientable Texture for Image-Based Pen- Texture for Image-Based Pen- and-Ink Illustration.” and-Ink Illustration.” Proceedings of Proceedings of SIGGRAPH 97. SIGGRAPH 97.

• Markosian

Markosian, , Kowalski Kowalski, and Hughes. “Real- , and Hughes. “Real- Time Time Nonphotorealistic Nonphotorealistic Rendering.” Rendering.” Proceedings of SIGGRAPH 97 Proceedings of SIGGRAPH 97. .

• Banks and Turk. “Image-guided

Banks and Turk. “Image-guided Streamline Placement.” Streamline Placement.” Proceedings of Proceedings of SIGGRAPH 96. SIGGRAPH 96.