Preliminary Study on Vision-based Pen-and-Ink Drawing by a Robotic Manipulator - PowerPoint PPT Presentation

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Preliminary Study on Vision-based Pen-and-Ink Drawing by a Robotic Manipulator

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Motivation Skill-dependent Motivation Time-consuming A. Robot Platform 5-DOF manipulator 0.1mm ... Canny edge detection ... image and object image: Idf ... – PowerPoint PPT presentation

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Title: Preliminary Study on Vision-based Pen-and-Ink Drawing by a Robotic Manipulator


1
Preliminary Study onVision-based Pen-and-Ink
Drawing by a Robotic Manipulator
Yan Lu, Josh Lam, Yeung Yam
The Chinese University of Hong Kong Dept. of
Mechanical and Automation Engineering
2
Outline
  • Motivation
  • Background
  • Methodology
  • Demonstration
  • Summary

3
Motivation
  • Pen-and-Ink is a traditional form of art,
    which is still popular today.

4
Motivation
  • Skill-dependent
  • Time-consuming

5
Background
  • A. Robot Platform
  • 5-DOF manipulator
  • 0.1mm movement
  • resolution
  • Visual feedback by
  • CCD camera

6
Background
  • B. Pen-and-Ink Properties
  • Stroke is monochromatic
  • Stroke contributes to both tone and texture
  • 3. Strokes work collectively, that is, no single
    one is of critical importance.

7
Methodology
  • Main challenge
  • Only monochromatic strokes can be used to
    convey three key aspects of an image
  • structural contents
  • tone brightness and darkness
  • and textures

8
Methodology
  • A. Structural Contents
  • Step 1. Outline extraction Canny edge detection
  • Step 2. Structural significance of edges
    measured by the lifetime in the Gaussian scale
    space of the original image (Orzan et al. 2007)

  • http//artis.imag.fr/Publications/2007/OBBT07/
  • Step 3. Outline delineation by strokes of
    different widths according to structural
    significance

9
Original image
Structural significance
10
Methodology
  • B. Tone Expression
  • The key is to place a stroke at a right
    location, based on the rule that strokes should
    be placed evenly close together in dark areas,
    and widely spaced in bright areas.
  • To accomplish this hatching process, we need
    the vision system to provide visual feedback.

11
Methodology
  • B. Tone Expression (Contd)
  • Step 1. Capture the current drawing by camera,
    blur it by an average filter, transfer it to top
    view by homography, denoted as Iop
  • Step 2. Compute the difference between current
    image and object image IdfIoj-Iop

12
Methodology
B. Tone Expression (Contd) Step 3. Determine the
importance image as Step 4. Place the next
stroke at the point where the value of the
importance image is the largest Step 5. Repeat
14 steps
Where i denotes the i -th stroke, and a is a
parameter, empirically set as 0.10.5.
13
Methodology
B. Tone Expression (Contd) Example of
determining stroke position
Object image Ioj
Current image Iop
Importance image Iip
14
Methodology
C. Texture Representation Strokes should be
appropriately orientated to represent desirable
textures. A natural way is to orientate a
stroke according to the gradient direction of the
original image. However, in practice, image
gradient directions are often too noisy to be
used directly.
15
Methodology
C. Texture Representation (Contd) Problem
illustration
By gradient
Original image
Local texture
16
Methodology
C. Texture Representation (Contd) Since
strokes work collectively, a local texture should
be expressed by a group strokes with consistent
orientations. We propose to select a set of
strong points whose gradients are large enough
to be believed, and calculate stroke direction by
interpolation using a few nearest strong
points.
17
Methodology
C. Texture Representation (Contd) Stroke
Orientation at p
Where pi is one of the n strong points nearest to
p, ?(pi) is the gradient direction at pi , and
d(p,pi) denotes the distance between p and pi .
18
Methodology
C. Texture Representation (Contd)
Strong points
By gradient
By gradient interpolation
19
Methodology
D. Stop Criterion A criterion function is
proposed to terminate the hatching process
automatically as follows
The first component is a descending function wrt.
stroke number i, while the second is an ascending
one. They work together to determine the stop
point.
20
Methodology
D. Stop Criterion (Contd)
The hatching process stops at the minimum point
of the criterion function, which can be tuned by
b.
b0.9, i1400
b1.0, i1000
21
Methodology
Overview
22
Demonstration
i0 i300 i700
i1026
i1283 i1502
23
(No Transcript)
24
Summary
  • We have presented a robotic system for
    automated Pen-and-Ink rendering
  • Structural contents delineated according to
    structural significance of edges
  • Tone expression based on visual feedback
  • Texture representation by interpolating local
    gradient directions
  • Automatic stop using a criterion function

25
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