Image Synthesis
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Transcript of Image Synthesis
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computer graphics & visualization
Image Synthesis
NPR – Non-photorealistic rendering
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computer graphics & visualization
Image Synthesis – WS 07/08Dr. Jens Krüger – Computer Graphics and Visualization Group
NP vs. NPR?
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computer graphics & visualization
Image Synthesis – WS 07/08Dr. Jens Krüger – Computer Graphics and Visualization Group
PR vs. NPR
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computer graphics & visualization
Image Synthesis – WS 07/08Dr. 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 07/08Dr. 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 07/08Dr. Jens Krüger – Computer Graphics and Visualization Group
ApplicationsArt
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computer graphics & visualization
Image Synthesis – WS 07/08Dr. Jens Krüger – Computer Graphics and Visualization Group
ApplicationsComics/ Cartoons
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computer graphics & visualization
Image Synthesis – WS 07/08Dr. Jens Krüger – Computer Graphics and Visualization Group
ApplicationsArchitecture
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computer graphics & visualization
Image Synthesis – WS 07/08Dr. Jens Krüger – Computer Graphics and Visualization Group
ApplicationsMaps
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computer graphics & visualization
Image Synthesis – WS 07/08Dr. Jens Krüger – Computer Graphics and Visualization Group
ApplicationsMaps
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computer graphics & visualization
Image Synthesis – WS 07/08Dr. Jens Krüger – Computer Graphics and Visualization Group
ApplicationsMedicine
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computer graphics & visualization
Image Synthesis – WS 07/08Dr. Jens Krüger – Computer Graphics and Visualization Group
ApplicationsMedicine
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computer graphics & visualization
Image Synthesis – WS 07/08Dr. Jens Krüger – Computer Graphics and Visualization Group
ApplicationsTechnicalIllustrations
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computer graphics & visualization
Image Synthesis – WS 07/08Dr. Jens Krüger – Computer Graphics and Visualization Group
ApplicationsArcheology
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computer graphics & visualization
Image Synthesis – WS 07/08Dr. Jens Krüger – Computer Graphics and Visualization Group
BasicsObject Space Screen Space3D 2DGeometry processing Image processingObject Precision Screen 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 07/08Dr. Jens Krüger – Computer Graphics and Visualization Group
AlgorithmsToon/Cell Shading
Sketching
Halftoning
Screening
Stippling
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computer graphics & visualization
Image Synthesis – WS 07/08Dr. 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 07/08Dr. 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 07/08Dr. Jens Krüger – Computer Graphics and Visualization Group
Toon ShadingColor 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 07/08Dr. Jens Krüger – Computer Graphics and Visualization Group
Toon ShadingSilhouettes (Screen Space)
• generate Depth map• find discontinuities
• generate normal map• find discontinuities
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computer graphics & visualization
Image Synthesis – WS 07/08Dr. Jens Krüger – Computer Graphics and Visualization Group
Toon ShadingCombination of both silhouette detections ideas:
Technical Illustrations:
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computer graphics & visualization
Image Synthesis – WS 07/08Dr. 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 07/08Dr. Jens Krüger – Computer Graphics and Visualization Group
Computer SketchingMotivation:• 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 07/08Dr. Jens Krüger – Computer Graphics and Visualization Group
Computer SketchingExample: 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 07/08Dr. 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 07/08Dr. Jens Krüger – Computer Graphics and Visualization Group
HalftoningAlgorithm:• Input: Gray scale image• Group pixles ( loss of image resolution)• Compute average intensity• Replace group by dither matrix
2 9 4
6 1 8
7 3 5
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computer graphics & visualization
Image Synthesis – WS 07/08Dr. 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 07/08Dr. Jens Krüger – Computer Graphics and Visualization Group
Error Diffusion
Floyd and Steinberg
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computer graphics & visualization
Image Synthesis – WS 07/08Dr. 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 07/08Dr. Jens Krüger – Computer Graphics and Visualization Group
ScreeningScreening with text
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computer graphics & visualization
Image Synthesis – WS 07/08Dr. 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 07/08Dr. 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 07/08Dr. 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 07/08Dr. Jens Krüger – Computer Graphics and Visualization Group
StipplingStipple 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 07/08Dr. Jens Krüger – Computer Graphics and Visualization Group
StipplingObject space:• prioritized line textures
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computer graphics & visualization
Image Synthesis – WS 07/08Dr. Jens Krüger – Computer Graphics and Visualization Group
Stippling• Other prioritized line textures
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computer graphics & visualization
Image Synthesis – WS 07/08Dr. Jens Krüger – Computer Graphics and Visualization Group
Stippling
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computer graphics & visualization
Image Synthesis – WS 07/08Dr. Jens Krüger – Computer Graphics and Visualization Group
Object / Image Space Stippling
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computer graphics & visualization
Image Synthesis – WS 07/08Dr. Jens Krüger – Computer Graphics and Visualization Group
Object / Image Space Stippling
black-and-white stippling
Supersampling in screen spacesurface based anti-aliasing