Computer Vision and Robotics

8/2/2019 Computer Vision and Robotics

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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/Magnification

Computer Vision and Robotics

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