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computer graphics & visualization NPR – Non-photorealistic rendering
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computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group NP vs. NPR?
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computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group PR vs. NPR
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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
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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
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computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Applications Art
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computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Applications Comics/ Cartoons
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computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Applications Architecture
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computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Applications Maps
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computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Applications Maps
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computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Applications Medicine
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computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Applications Medicine
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computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Applications Technical Illustrations
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computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Applications Archeology
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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“)
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computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Algorithms Toon/Cell ShadingSketchingHalftoningScreeningStippling
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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
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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
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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
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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
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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 :
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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
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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
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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
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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
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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 matrix294618 735
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computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Halftoning limited resolution of the human visual system
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computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Error Diffusion Floyd and Steinberg
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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
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computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Screening Screening with text
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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
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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
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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
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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
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computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Stippling Object space: prioritized line textures
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computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Stippling Other prioritized line textures
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computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Stippling
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computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Object / Image Space Stippling
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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
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