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Introduction to Grayscale and Color Images

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EE465: Introduction to Digital Image Processing. 1 ... Kodak Easyshare. Photography 101. pros. Interchangable lens. Greater quality and lower noise ... – PowerPoint PPT presentation

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Title: Introduction to Grayscale and Color Images


1
Introduction to Grayscale and Color Images
  • Image acquisition
  • Light and Electromagnetic spectrum
  • Charge-Coupled Device (CCD) imaging and Bayer
    Pattern (the most popular color-filter-array)
  • Sampling and Quantization
  • Image representation
  • Spatial resolution
  • Bit-depth resolution
  • Local neighborhood
  • Block decomposition

2
Electromagnetic spectrum
3
Light the Visible Spectrum
  • Visible range 0.43µm(violet)-0.78µm(red)
  • Six bands violet, blue, green, yellow, orange,
    red
  • The color of an object is determined by the
    nature of the light reflected by the object
  • Monochromatic light (gray level)
  • Three elements measuring chromatic light
  • Radiance, luminance and brightness

4
Sensor Array CCD Imaging
5
Charge coupled device (CCD) image sensor
http//en.wikipedia.org/wiki/Charge-coupled_device
6
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7
Complementary Metal Oxide Semiconductor (CMOS)
Image Sensor
http//www.dalsa.com/corp/markets/CCD_vs_CMOS.aspx
8
Image Formation Model
f(x,y)i(x,y)r(x,y)n(x,y)
0ltf(x,y)lt8
Intensity proportional to energy radiated by a
physical source
0lti(x,y)lt8
illumination
0ltr(x,y)lt1
reflectance
(intrinsic images)
n(x,y)
noise
9
Sampling and Quantization 1D Case
10
2D Sampling and Quantization
11
3D Visualization
It is useful to take an analogy to rain gauge
(image intensity values Measure the amount of
photon rain)
12
Color Imaging Bayer Pattern
38,990
309
US3,971,065
http//en.wikipedia.org/wiki/Bayer_pattern
http//ask.metafilter.com/17138/3CCD-vs-1CCD
13
Demosaicing (CFA Interpolation)
14
Simple Ideas Linear Interpolation
You will be asked to try these simple ideas in
CA2
15
Biological vs. Artificial Sensors
Cone distribution in human retina
US3,971,065
Question Engineers invention vs. natures
evolution, who wins?
16
Digital Single-Lens Reflection (DSLR) Cameras
17
Nikon D50
18
Kodak Easyshare
19
Photography 101
  • pros
  • Interchangable lens
  • Greater quality and lower noise
  • Suitable for high-motion and low-light
    environment
  • Better focusing capability
  • Larger focal length
  • Cons
  • Larger and heavier
  • More expensive
  • Lack of video mode
  • Sensor dust problem
  • More difficult to focus on very close objects

20
The Plague in Photography Motion Blur
21
High Dynamic Range Imaging
Q Can we generate a HDR image (16bpp) by a
standard camera? A Yes, adjust the exposure and
fuse multiple LDR images together
22
HDR Display (After Toner Mapping)
Note that any commercial display devices we see
these days are NOT HDR
23
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24
Beyond Visible
  • Gamma-ray and X-ray medical and astronomical
    applications
  • Infrared (thermal imaging) near-infrared and
    far-infrared
  • Microwave imaging
  • Radio-frequency MRI and astronomic applications

25
Thermal Imaging
Operate in infrared frequency
Grayscale representation (bright pixels correlate
with high-temperature regions)
Pseudo-color representation (Human body
dispersing heat denoted by red)
26
Low Signal-to-Noise (SNR) Behavior
noise
signal
27
Radar Imaging
Operate in microwave frequency
Mountains in Southeast Tibet
28
Synthetic Aperture Radar (SAR)
  • Environmental monitoring, earth-resource mapping,
    and military systems
  • SAR imagery must be acquired in inclement weather
    and all-day-all-night.
  • SAR produces relatively fine azimuth resolution
    that differentiates it from other radars.

29
Magnetic Resonance Imaging (MRI)
Operate in radio frequency
knee
spine
head
30
Basic Principle of MRI
k-space
IFT
31
Comparison of Different Imaging Modalities
infrared
radio
visible
32
Fluorescence Microscopy Imaging
Operate in ultraviolet frequency
normal corn
smut corn
33
What Does a Neuron Look Like?
Artistic illustration
Real image
34
X-ray Imaging
Operate in X-ray frequency
chest
head
35
Positron Emission Tomography
Operate in gamma-ray frequency
36
Mechanical Categorization of Sensors
  • Motionless imaging
  • Sensor is kept still during the acquisition
    (e.g., CCD cameras)
  • Motion-aided imaging
  • Sensor moves along a line or rotates around a
    center during the acquisition (e.g., document
    scanning and MRI scanning)
  • Subtle relationship between visual perception and
    motion
  • We move because we see we see because we move
    J. Gibson

37
Single-sensor Imaging
38
Motion Aids Imaging
39
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40
Introduction to Grayscale Images
  • Image acquisition
  • Light and Electromagnetic spectrum
  • Charge-Coupled Device (CCD) imaging
  • Sampling and Quantization
  • Image representation
  • Spatial resolution
  • Bit-depth resolution
  • Local neighborhood
  • Block decomposition

41
Image Represented by a Matrix
Spatial resolution
Bit-depth resolution
42
Spatial Resolution
43
Image Resampling
44
Towards Gigapixel
Mega-pel
Giga-pel
Photographers and artists have manually or
semi-automatically stitched hundreds of mega-pel
pictures together to demonstrate how a giga-pel
picture looks like ? the power of pixels
http//triton.tpd.tno.nl/gigazoom/Delft2.htm
45
Aliasing in Digital Images
46
Bit-depth Resolution
47
Bit-depth Resolution (Cond)
48
Commonlyused Terminology
Neighbors of a pixel p(i,j)
N8(p)(i-1,j),(i1,j),(i,j-1),(i,j1), (i-1,j-1),
(i-1,j1),(i1,j-1),(i1,j1)
N4(p)(i-1,j),(i1,j),(i,j-1),(i,j1)
Adjacency
4-adjacency p,q are 4-adjacent if p is in the
set N4(q)
8-adjacency p,q are 8-adjacent if p is in the
set N8(q)
Note that if p is in N4/8(q), then q must be also
in N4/8(p)
49
Common Distance Definitions
D8 distance (checkboard distance)
D4 distance (city-block distance)
Euclidean distance (2-norm)
2
2
2
2
2
2
3
3
4
4
2
1
1
1
1
1
2
2
2
2
3
3
1
1
0
1
1
0
1
2
0
1
2
2
2
2
2
1
1
1
3
1
1
2
2
2
3
2
2
2
2
3
3
4
4
2
2
2
2
50
Block-based Processing
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