Introduction to Grayscale and Color Images

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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

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Electromagnetic spectrum
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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

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Sensor Array CCD Imaging
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Charge coupled device (CCD) image sensor
http//en.wikipedia.org/wiki/Charge-coupled_device
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Complementary Metal Oxide Semiconductor (CMOS)
Image Sensor
http//www.dalsa.com/corp/markets/CCD_vs_CMOS.aspx
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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
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Sampling and Quantization 1D Case
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2D Sampling and Quantization
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3D Visualization
It is useful to take an analogy to rain gauge
(image intensity values Measure the amount of
photon rain)
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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
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Demosaicing (CFA Interpolation)
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Simple Ideas Linear Interpolation
You will be asked to try these simple ideas in
CA2
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Biological vs. Artificial Sensors
Cone distribution in human retina
US3,971,065
Question Engineers invention vs. natures
evolution, who wins?
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Digital Single-Lens Reflection (DSLR) Cameras
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Nikon D50
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Kodak Easyshare
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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

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The Plague in Photography Motion Blur
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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
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HDR Display (After Toner Mapping)
Note that any commercial display devices we see
these days are NOT HDR
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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

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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)
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Low Signal-to-Noise (SNR) Behavior
noise
signal
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Radar Imaging
Operate in microwave frequency
Mountains in Southeast Tibet
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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.

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Magnetic Resonance Imaging (MRI)
Operate in radio frequency
knee
spine
head
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Basic Principle of MRI
k-space
IFT
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Comparison of Different Imaging Modalities
infrared
radio
visible
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Fluorescence Microscopy Imaging
Operate in ultraviolet frequency
normal corn
smut corn
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What Does a Neuron Look Like?
Artistic illustration
Real image
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X-ray Imaging
Operate in X-ray frequency
chest
head
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Positron Emission Tomography
Operate in gamma-ray frequency
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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

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Single-sensor Imaging
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Motion Aids Imaging
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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

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Image Represented by a Matrix
Spatial resolution
Bit-depth resolution
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Spatial Resolution
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Image Resampling
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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
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Aliasing in Digital Images
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Bit-depth Resolution
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Bit-depth Resolution (Cond)
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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)
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Common Distance Definitions
D8 distance (checkboard distance)
D4 distance (city-block distance)
Euclidean distance (2-norm)
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Block-based Processing