Aesthetic Computing and Shape Chapter 14

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Aesthetic Computing and Shape (Chapter 14)

• John Nichols, Beau Hollis, Jay DiVilbiss

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Overview

• Gestalt Principles
• Mathematical representation of structure Medial
  Axis
• Shock Scaffolding

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The Beauty of Shape

• The human face What constitutes beauty?
• The nose of a Nefertiti or David?
• Eyes The round pattern of the iris, with its
  varying, yet repetitive set of colored patches?
• These can be beautiful, but what of the face as a
  whole?

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The Beauty of Shape

• Beautiful eyes can look funny if their
  interdistance is too large or too small, with
  respect to the remaining overall figure,
  especially the nose.
• Same rationale could be applied to the lips,
  ears, etc.
• The juxtaposition of elements and their
  relationships with one another account for
  passing or failing the test of beauty in the
  eyes of humans.

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The Whole Package

• e.g. Jessica Simpson
• The same idea can be applied to most pictures
  registered by the brain photograph, painting,
  drawing, etc.
• Psychologists and art historians have long
  attempted to objectify the beauty of shape in
  order to provide physical theories for analyzing
  human perception and works of art.
• This lead to the Gestalt Theory.

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Gestalt Psychology

• founded by Max Wertheimer (1880 1943)
• Was, to some extent, a rebellion against the
  molecularism of Wundts program for psychology of
  the time.
• Gestalt means a unified or meaningful whole.
• Shift the focus of psychological study from parts
  to whole.
• Since the late 1800s, Gestalt Psychologists
  noticed that the human eye is sensitive to
  illusory patterns, creating paths of
  relationships where there is no signal (e.g.
  optical illusions).

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1.) Figure and Ground

• These terms explain how we elements of the scene
  which are similar in appearance and shape and
  group them together as a whole.
• Similar elements (figure) are contrasted with
  dissimilar elements (ground).
• A good whole is often characterized as the
  figure, which means the figure usually
  incorporates more than one Gestalt Principle.
• Closedness is one key principle in establishing
  the figure.

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2.) Closure

• We tend to see complete figures, even when part
  of the information is missing.
• Our minds react to patterns that are familiar.
• Speculated to be a survival instinct, allowing us
  to detect the complete form of a predator, even
  with incomplete information.

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3.) Area

• The smaller of two overlapping figures is
  perceived as figure, while the larger is regarded
  as ground.
• We perceive the smaller square to be a shape on
  top of the other figure, as opposed to a hole in
  the larger shape.
• We can use shading to get our point across and
  reverse this effect.

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4.) Symmetry

• The whole of a figure is perceived rather than
  the individual parts which make up the figure.
• What do you see to the right? Two overlapping
  diamonds, or three objects a small diamond and
  two irregular objects above and below it?
• Most people would perceive according to the
  principle of symmetry, thus seeing two diamonds
  overlapping.

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5.) Similarity

• Things which share visual characteristics such as
  shape, size, color, texture, value or orientation
  will be seen as belonging together.
• Above right The two filled lines gives our eyes
  the impression of two horizontal lines, even
  though all the circles are equidistant from each
  other.
• Bottom right The larger circles appear to belong
  together because of the similarity in size.

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6.) Proximity or Contiguity

• Features that are spatially close together are
  grouped together perceptually.
• Since the horizontal rows of circles are closer
  together than the vertical columns, we perceive
  vertical lines.
• Further, since the first two columns and the last
  two columns have less space between them than the
  center two columns, we perceive two groups of two
  columns.

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7.) Continuity

• Lines based on smooth continuity are preferred
  over abrupt changes of direction.
• We perceive the figure as two crossed lines
  instead of 4 lines meeting at the center.

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Rudolph Arnheim

• Arnheim was a student of the German Gestalt
  school of the early 1900s.
• Applied these Gestalt Principles to the arts,
  including cinema, sculpting, painting and
  drawing.
• Thought of the visual experience as a field of
  forces, with its balance, dynamics, and lines of
  main attraction and repulsion.

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Computational Models

• Gestalt school provided insights and guidelines
  into understanding of how shape is perceived.
• However, it lacked a clear mathematical framework
  for a computation model of the aesthetics of
  shape, its implementation, and use.

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The Medial Axis of Blum

• Harry Blum
• Radio Engineer
• Mathematical framework based on the notion of
  wave propagation

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Grassfire Analogy

• Equidistant from two different parts of the
  boundary
• Locus of these quench points is the medial axis

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Maximal Discs

• Meeting wave fronts initiated from the boundary
  and navigating at constant speedsalso..
• Empty discs tangent to one boundary growing until
  it becomes tangent with two or more

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Maximal Discs

• (Middle empty disc expanding)
• (Bottom wave fronts converging)

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Directed Paths

• Obtained by taking the distance of converging
  wave fronts or radii of empty discs
• Arrows indicate direction of increasing distance

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Skeletonization/MAT

• Process for reducing foreground regions while
  still preserving the size and connectivity of the
  original object
• Created using Blums process

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Medial Hierarchies

• Medial Axis is a continuous structure that
  branches at various places

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Medial Hierarchies

• Each Branch in the hierarchy corresponds to a
  different piece of the object each bump on
  the object is a branch, etc.
• Triple Points - Qualitative differences in
  objects seen where three branches meet
• Length Original objects length obtained from
  distance of one endpoint to another

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Problems with the Medial Axis

• Thresholding grayscale/color images
• Difficult to obtain ideal binary image

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Problems with the Medial Axis

• Unexpected binary images produce complex and
  confusing medial axis

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Problems with the Medial Axis

• Noise
• Medial axis is extremely sensitive to noise
• Each noise point in the original object has a
  branch connected to it in the skeleton

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Interactive Skeletonization Experimentation

• Link to experiment
• http//homepages.inf.ed.ac.uk/rbf/HIPR2/skeletonde
  mo.htm
• Image to load http//homepages.inf.ed.ac.uk/rbf/
  HIPR2/images/wdg2thr3.gif
• Phone http//homepages.inf.ed.ac.uk/rbf
  /HIPR2/images/phn1thr1.gif

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Shock Scaffolding

• 3D graph
• describes the shape of an object
• Uses medial access data
• Has a flexible hierarchical structure

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Types of Contact

• Use A notation to denote number of tangent curves
  and the degree of curvature at the tangent point.
• Only odd degree curvatures are suitable for
  contact spheres.

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Singularity Flow

• The flow for each MA point is defined in the
  direction of increasing radius, R, of associated
  maximal contact spheres in a neighborhood of that
  point.
• This flow itself can have singularities, and
  shocks thereby can flow along sheets or curves
  in various ways

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Types of Shock Points
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Reduced shock scaffold (SC-)

• The reduced shock scaffold is the SC where link
  attributes (i.e., geometry and dynamics) have
  been discarded.

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Shock Scaffolding (SC)

• The shock scaffold is a directed graph, with
  nodes P and links L.

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Augmented Shock Scaffold (SC)

• The augmented shock scaffold, is the MA
  augmented with the set of shock nodes, P,
  connected by links L and hyperlinks H.

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Shock Hypergraph

• The shock hypergraph, SH, adds to SC sources,
  relays and sinks of shock sheets (indicated as
  blue squares) and links amongst these as well as
  with respect to the sheet boundaries.

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Examples
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Criticism

• Good technical overview, but doesnt explain its
  connection to rules of Aesthetics
• Not many examples of the uses of Medial Axis or
  Shock Scaffolding
• Difficult to understand

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• Works Cited
• Gestalt Principles Examples and Explaination
• http//www1.cs.columbia.edu/paley/spring03/assig
  nments/HWFINAL/es481/principlestable.html
• Gestalt Principles of Perception
• http//www.usask.ca/education/coursework/skaalid/
  theory/gestalt/gestalt.htm
• Gestalt Principles Web Design
• http//tepserver.ucsd.edu/jlevin/gp/index.html
• Bryan S. Morse. Shape Description (Regions,
  contd).
• http//homepages.inf.ed.ac.uk/rbf/CVonline/LOCAL_
  COPIES/MORSE/medial.pdf
• Hypermedia Image Processing Reference (HIPR2).
  Skeletonization/Medial Axis Transform.
• http//homepages.inf.ed.ac.uk/rbf/HIPR2/skeleton.
  htm
• Benjamin B. Kimia. On The Role of Categories
  in Recognition of 2D Shapes
• http//www.mis.informatik.tu-darmstadt.de/events/
  cvpr04-gorc/talks/6-kimia.pdf