NPR Non-photorealistic rendering Umesh .A Bhat {umesh@ut.ee} The - - PowerPoint PPT Presentation

▶
npr
SMART_READER_LITE
LIVE PREVIEW

NPR Non-photorealistic rendering Umesh .A Bhat {umesh@ut.ee} The - - PowerPoint PPT Presentation

Oct 20, 2022 245 likes •601 views

OCT 26, 2015 NPR Non-photorealistic rendering Umesh .A Bhat {umesh@ut.ee} The Opposite of making things look real... Watercolors SRC: Lunar Studio Exploded view SRC: Wikipedia Exploded view (complex) SRC: General Electric Ink wash

slide-1
SLIDE 1

NPR

Non-photorealistic rendering

Umesh .A Bhat {umesh@ut.ee}

OCT 26, 2015

slide-2
SLIDE 2

The “Opposite” of making things look real...

slide-3
SLIDE 3

Watercolors

SRC: Lunar Studio

slide-4
SLIDE 4

Exploded view

SRC: Wikipedia

slide-5
SLIDE 5

Exploded view (complex)

SRC: General Electric

slide-6
SLIDE 6

Ink wash (Sumi-e)

SRC: GamesRadar Sumiesociety

slide-7
SLIDE 7

NPR is also known as...

  • Expressive graphics
  • Artistic rendering
  • Non-realistic graphics
  • Art-based rendering
  • Psychographics

SRC: Yao et. al 2011

slide-8
SLIDE 8

Why ?

slide-9
SLIDE 9

Why ?

SRC: Marc Benjamin Zinck Carnegie Mellon University

slide-10
SLIDE 10

“A means of creating imagery that does not aspire to realism” - Stuart Green

slide-11
SLIDE 11

Hue

Perception of “distinct” colors by humans

Tones

Perception of brightness of a color by humans

SRC: Wikipedia

slide-12
SLIDE 12

Two fundamental cues

Silhouette – the visible edges of a surface Hatching – the use of texture to indicate the

local orientation (shading) of a surface

SRC: Salisbury et al. 1997

slide-13
SLIDE 13

NPR can also be classified as

  • Model based NPR
  • Image based NPR

SRC: Doug DeCarlo and Anthony Santella 2002, Winkenbach and Salesin 1996

slide-14
SLIDE 14

Model based NPR

Camera Light 3D Model

Visible polygons Illumination Textures

slide-15
SLIDE 15

Image based NPR

Pen-and-ink drawings Water-color paintings Cartoon style

slide-16
SLIDE 16

NPR – rendering polygonal surfaces

3D Model Lighting Camera Visible polygons Procedural stroke texture Stroke clipping Outline drawing How much 3D information do we preserve ? We will collect a reference image here to indicate desired tone (lightness or darkness) at each pixel

slide-17
SLIDE 17

NPR Categories

  • Pen-and-ink illustration
  • Painterly rendering
  • Cartoons
  • Technical illustrations
  • Scientific visualization
slide-18
SLIDE 18

Pen-and-ink illustrations

user input reference image rendered output

SRC: Winkenbach and Salesin 1994

slide-19
SLIDE 19

Pen-and-ink illustrations

Strokes Curved lines of varying thickness and density Texture Conveyed by collection of strokes Tone Perceived gray level across image or segment Outline Boundary lines that disambiguate structure

SRC: Winkenbach and Salesin 1994

slide-20
SLIDE 20

Strokes and Stroke Textures

Strokes are generated by moving along straight path Strokes are perturbed by

  • Waviness function (straightness)
  • Pressure function (thickness)

Collected in stroke textures

  • Tone dependent
  • Resolution dependent
  • Orientation dependent

SRC: Winkenbach and Salesin 1994

slide-21
SLIDE 21

NPR – rendering parametric surfaces

  • Uses parametric directions as stroke directions
  • Maintain constant tone
  • Varying tone based on lighting
  • Can be combined with texture-mapping

SRC: Winkenbach and Salesin 1996

slide-22
SLIDE 22

NPR – rendering general surfaces

  • Placing strokes along a direction field
  • The field is either computed

automatically or designed by user

SRC: Hertzmann and Zorin 2000

slide-23
SLIDE 23

Automatic painting

Start from color image: no 3D information Paint in resolution-based layers

  • Blur to current resolution
  • Select brush based on current resolution
  • Find area of largest error compared to real image
  • Place stroke
  • Increase resolution and repeat

Layers are painted coarse-to-fine Styles controlled by parameters

SRC: Hertzmann

Blurring Adding detail with smaller strokes

slide-24
SLIDE 24

Painting styles

Style determined by parameters

  • Approximation thresholds
  • Brush sizes
  • Curvature filter
  • Blur factor
  • Minimum and maximum stroke lengths
  • Opacity
  • Grid size
  • Color jitter

Encapsulate parameter settings as style

slide-25
SLIDE 25

Cartoon shading

  • Silhouette edge detection
  • Cartoon shading

The illumination is computed at discrete levels (often 2) between the fully lit illumination and shadow (ambient) color, determined by n.L 2 texels

SRC: [1]

slide-26
SLIDE 26

Cartoon shading

SRC: Lake et. al, NPAR 2000

slide-27
SLIDE 27

Technical illustrations

Level of abstraction

  • Accentuate important 3D properties
  • Diminish or eliminate extraneous details

Does not represent reality Black edge lines Cool to warm shading colors Single light source Shadows rarely used

SRC: SAM Aircraft

slide-28
SLIDE 28

Technical illustrations

Phong shading Metal shading Edge lines Gooch shading

SRC: Gooch et. al 96

slide-29
SLIDE 29

Technical illustrations

Phong shading Metal shading Edge lines Gooch shading

SRC: Gooch et. al 96

slide-30
SLIDE 30

Cel shading

  • The back faces are drawn with thick lines
  • The object is drawn with a basic texture
  • Shading

SRC: Wikipedia

slide-31
SLIDE 31

Cel shading

depth and world-space surface normal screen-sized color texture Sobel filter or similar edge-detection filter

SRC: Wikipedia

slide-32
SLIDE 32

Cel shading

Result

SRC: Wikipedia

slide-33
SLIDE 33

Presentations

[1] http://classes.cec.wustl.edu/~cse452/lectures/lect14_NPR.pdf [2] http://graphics.cs.cmu.edu/nsp/course/15-462/Spring04/slides/21-npr.pdf [3] http://run.usc.edu/cs420-s15/lec24-npr/24-npr.pdf [4] http://www.cs.ucr.edu/~vbz/cs130f14-14.pdf [5] http://gfx.cs.princeton.edu/proj/sg05lines/course7-4-npr.pdf

Select references

Papers

[6] https://cseweb.ucsd.edu/~ravir/npr_materials.pdf [7] https://www.academia.edu/2620342/State_of_the_art_non-photorealistic_rendering_NPR_techniques [8] http://www.cs.northwestern.edu/~bgooch/PDFs/gooch98.pdf

Book

Non-Photorealistic Rendering Bruce Gooch and Amy Gooch. A.K. Peters Ltd. Publishers ISBN: 1-56881-133-0

slide-34
SLIDE 34

SRC: Reddit

slide-35
SLIDE 35

Feel free to ping me at {umesh@ut.ee}

Typos ? Corrections ? Left something out ?