CSCE 452 ROBOT VISION
Introduction to Computer VisionDezhen Song,
Department Computer Science and EngineeringTexas A&M University
Part of slides are from Bahadir K. Gunturk’s EE4780
Digital Image Acquisition
Imaging Sensors Charge-Coupled Device (CCD)
Imaging Sensors Complementary Metal Oxide
Semiconductor (CMOS)
CCD Vs. CMOS
Responsivity: CMOS >CCD Dynamic range: CCD is 2 times better Uniformity: CCD > CMOS Shuttering
CCD: synchronous shutter (better) CMOS: rolling shutter
Speed: CMOS >> CCD Reliability: CMOS >>CCD Cost: CMOS < CCD
Bahadir K. Gunturk 6
Matrix Representation of Images
A digital image can be written as a matrix
1 2
[0,0] [0,1] [0, 1]
[1,0] [1,1] [1, 1][ , ]
[ 1,0] [ 1, 1]MxN
x x x N
x x x Nx n n
x M x M N
35 45 20
43 64 52
10 29 39
RGB Color Model
Dynamic range (Contrast Ratio)
Nature light: 1010:1 Human eye: 109:1 CMOS Sensor: 11000-6000:1 LCD panel: 1000-10000:1
Measured Dynamic Range
Bit Precisionof A/D Converter
Contrast Ratio
8 256:110 1024:112 4096:114 16384:116 65536:1
10
ExposuresLong exposure time
Short exposure time
Cameras
2D camera (i.e. surveillance camera) Pin-hole camera Surveillance camera Robotic pan-tilt-zoom camera Wide angle camera –
fisheye, omni, etc 1D camera (satellite camera, scanner) Photo cell
12
Perspective Projection Perspective projection equations
' ' 'x y z
x y z
13
Pinhole Camera Model
14
Cameras With Lenses Most cameras are equipped with lenses. There are two main reasons for this:
To gather light. To keep the picture in sharp focus while gathering
light from a large area.
15
Real Lenses Rays may not focus at a single point.
Spherical aberration
Spherical aberration can be eliminated completely by designing aspherical lenses.
Bahadir K. Gunturk 16
Real Lenses
Chromatic Aberration
Bahadir K. Gunturk 17
Real Lenses Special lens systems using two or more pieces of glass with
different refractive indeces can reduce or eliminate this problem. However, not even these lens systems are completely perfect and still can lead to visible chromatic aberrations.
Finite projective camera
1yx
xx
p
ps
K
C~|IKRP
11 dof (5+3+3)
Camera Calibration
Bahadir K. Gunturk 20
Compound Lens Systems
Lens modelling Thin lens Thick lens Lens with mirrors Radial Distortion
22
Real Lenses Barrel Distortion & Pincushion Distortion
Stop (Aperture)
Causes of distortion
(normal)
Chief ray