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Computer Vision & Robotics
Dr Suprava Patnaik
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What???
- Modeling & replicating human vision system (AI)
- A field that includes methods for acquiring,processing, analysing, and understanding images
Challenges???
- Computing properties of the 3D world from one ormore digital images
- Interpretations are ambiguous
- Forward problem(Graphics) vs Inverse problem(CV)
- Changing view point, Moving light source, Shapedeformation.
How??
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Applications: touching our life
Sports
Movies
Surveillance
HCI hand gestures, Hand gesture & signed
language
Face recognition &
Biometrics Road monitoring
Industrial inspection
Robotic control
Autonomous driving
Space: planetary
exploration, docking Medicine pathology,
surgery, diagnosis
Microscopy
Military
Remote Sensing
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Course Coverage
Computer Vision
Basics of Imaging, Low level & High level
Processing, Representation and Interpretation
Robotics
Introduction to Robot dynamics & Kinematics
Microcontroller & Simple Programing
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IMAGE FORMATION
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Pinhole Camera It is a first order approximation of sensing devices
like eyes and camera, used for mapping from a
3D scene to 2D image.
Captures pencil of rays all rays through a single
point through a pinhole called Center ofProjection (COP)
Image is formed on the Image Plane. Effective
focal length fis distance from COP to Image Plan
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Magnification
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Orthographic projection (m=1)
Object Dimension are preserved from one view to other
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Weak-Perspective
Approximation of perspective projection byorthographic projection followed by scaling.
Conditions:
- Object dimensions are small compared to thedistance of the object from the center ofprojection
- Object is close to the principal axis : linepassing through the center of projection andcenter of image plane
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Assignment-1
For different dimensions compare the
difference between the orthographic and
perspective volume.
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Problems with Pinholes
Pinhole size (aperture) must be very small to
obtain a clear image.
However, as pinhole size is made smaller, less light
is received by image plane.
If pinhole is comparable to wavelength of
incoming light, DIFFRACTION
effects blur the image!
Sharpest image is obtained when:
pinhole diameter
Example: Iff = 50mm,
= 600nm (red),
d = 0.36mm
'2 fd
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Why Lens
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Image Formation using Lenses
Lenses are used to avoid problems with pinholes.
Ideal Lens: Same projection as pinhole but gathers more light!
i o
foi
111Gaussian Lens Formula:
f is the focal length of the lensdetermines the lenss ability to bend (refract) light
P
P
f
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Two Lens System
Rule : Image formed by first lens is the object for the second lens.
Main Rays : Ray passing through focus emerges parallel to optical axis.
Ray through optical center passes un-deviated.
image
plane
lens 2 lens 1
object
intermediate
virtual image
1i
1o
2i
2o
2f
1f
finalimage
d
Magnification:
1
1
2
2
o
i
o
im
Exercises: What is the combined focal length of the system?
What is the combined focal length if d = 0?
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Focus and Defocus
foi
111
Depth of Field: Range of object distances over which image is sufficiently well focused.
i.e. Range for which blur circle is less than the resolution of the imaging sensor.
d
aperture
diameter
aperture
foi
1
'
1
'
1Gaussian Law:
Blur Circle, b
)'()()'(
)'( oofo
f
fo
fii
Blur Circle Diameter : )'('
iii
db
i
'i
o
'o
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Varying Focus
There is a specific distance at which objects are in focus
other points project to a circle of confusion in the image
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Depth of Field
http://www.cambridgeincolour.com/tutorials/depth-of-field.htm
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Aperture(d) controls Depth of Field
Changing the aperture size affects depth of field A smaller aperture increases the range in which the
object is approximately in focus
But small aperture reduces amount of light need to
increase exposure
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Varying the aperture
f/2.8Large apeture = small DOF
f/22Small apeture = large DOF
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f
FOV depends of Focal Length
Smaller FOV = larger Focal Length
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Field of View (Zoom)
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Field of View (Zoom)
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Large Focal Length compresses depth
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Field of View / Focal Length
Large FOV
Camera close to car
Small FOV
Camera far from the car
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Large Focal Length compresses depth
1995-2005 Michael Reichmann
400 mm 200 mm 100 mm 50 mm 28 mm 17 mm
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Lens Flaws: Chromatic Aberration
Dispersion: wavelength-dependent refractive index (enables prism to spread white light beam into rainbow)
Modifies ray-bending and lens focal length: f()
color fringes near edges of image
Corrections: add doublet lens of flint glass, etc.
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Chromatic Aberration
Near Lens Center Near Lens Outer Edge
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VIGNETTING
Light incident on the sensor at a right angle
produces a stronger signal than light hitting it
at an oblique angle
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Radial Distortion (e.g.Barrel and pin-cushion)
straight lines curve around the image center
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Radial Distortion
Radial distortion of the image Caused by imperfect lenses
Deviations are most noticeable for rays that pass through theedge of the lens
in "barrel distortion", image magnification decreases withdistance from the optical axis.
In "pincushion distortion", image magnification increases with thedistance from the optical axis.
No distortion Pin cushion Barrel
http://en.wikipedia.org/wiki/Optical_axishttp://en.wikipedia.org/wiki/Magnificationhttp://en.wikipedia.org/wiki/Optical_axishttp://en.wikipedia.org/wiki/Optical_axishttp://en.wikipedia.org/wiki/Optical_axishttp://en.wikipedia.org/wiki/Optical_axishttp://en.wikipedia.org/wiki/Optical_axishttp://en.wikipedia.org/wiki/MagnificationTop Related