computer graphics & visualization NPR – Non-photorealistic rendering

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group NP vs. NPR?

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group PR vs. NPR

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Why NPR? “Science”: Convey information more efficiently by reduction, abstraction, accentuation “Art”: create novel artistic, creative imagery

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Reasons against photorealism? Too much (unnecessary) information  maps, technical/medical illustrations Constraints Creativity  improper for caricatures, comics, art Time consuming image generation  (probably) not feasible for real-time applications No room for the fantasy of the viewer „Photorealism, like pornography, leaves nothing to the imagination“ - Cassidy Curtis

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Applications Art

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Applications Comics/ Cartoons

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Applications Architecture

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Applications Maps

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Applications Maps

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Applications Medicine

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Applications Medicine

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Applications Technical Illustrations

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Applications Archeology

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Basics Object Space Screen Space 3D 2D Geometry processing Image processing Object PrecisionScreen Precision Pseudo code: „for each Object do…“ Pseudo code: „for each Pixel do…“ Usually does not require recomputation on affine transformations Recomputation every time the image changes (  no frame-to-frame coherence „Shower Door Effect“)

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Algorithms Toon/Cell ShadingSketchingHalftoningScreeningStippling

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Toon Shading Toon/Cell Shading: Rendering technique to create cartoon like movies

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Toon Shading -large homogenous regions -very few colors -enhanced silhouettes -simple geometry -reduction to important elements Motivation: Simpel and (semi-) automatic (mass-) production of comics

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Toon Shading Color computation (object space): precompute 2-3 shades for each color (Light-/ Shadow- color) and store them in a 1D texture assignment of final color by 1D texture lookup 1D texture surface

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Toon Shading Silhouettes (Screen Space) generate Depth map generate Depth map find discontinuities find discontinuities generate normal map generate normal map find discontinuities find discontinuities

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Toon Shading Combination of both silhouette detections ideas: Technical Illustrations :

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Sketching Sketching: Automatic method to create computer images that look like and hand-made drawings

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Computer Sketching Motivation: Ideal to present concepts (architecture) Precise Depiction often looks very sterile Methods: Use special output device Image space post-processing Object space 3D model modification

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Computer Sketching Example: Object space approach: Pseudo-Randomly change length of lines Cut lines into multiple sub-lines Move line center

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Halftoning Halftoning: Reproduce (color/grayscale) images with a (very) limited amount of colors, usually only black/white “Historically”, a necessity to print images in newspapers

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Halftoning Algorithm: Input: Gray scale image Group pixles (  loss of image resolution) Compute average intensity Replace group by dither matrix

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Halftoning limited resolution of the human visual system

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Error Diffusion Floyd and Steinberg

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Screening Bild Screening: Artistic variation of the halftoning algorithm Replaces the simple dither matrix by one ore more complex images

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Screening Screening with text

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Stippling Stippling: Construct an image of a large number of dots

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Pointillismus Georges Seurat - Ein Sonntagnachmittag auf der Insel La Grande Jatte

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Stippling Motivation: Results in very “clean/cold” illustrations Very time-consuming to create manually Applications: Scientific and technical illustrations Art Print media

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Stippling Stipple points simulate both tone and texture. Usually a uniform distribution without any recognizable pattern is used

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Stippling Object space: prioritized line textures

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Stippling Other prioritized line textures

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Stippling

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Object / Image Space Stippling

computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Object / Image Space Stippling black-and-white stippling Supersampling in screen space surface based anti-aliasing