ee.sharif.edu/~dip E. Fatemizadeh, Sharif University of Technology, 2011 1 Digital Image Processing Digital Image Fundamental • Digital Image Fundamentals: – Elements of Visual Perception – Light and the Electromagnetic Spectrum – Image Sensing and Acquisition – Image Sampling and Quantization – Some Basic Relationships between Pixels – An Introduction to the Mathematical Tools Used in Digital Image Processing
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ee.sharif.edu/~dip
E. Fatemizadeh, Sharif University of Technology, 2011
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Digital Image Processing
Digital Image Fundamental
• Digital Image Fundamentals:
– Elements of Visual Perception
– Light and the Electromagnetic Spectrum
– Image Sensing and Acquisition
– Image Sampling and Quantization
– Some Basic Relationships between Pixels
– An Introduction to the Mathematical Tools Used in Digital Image Processing
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Digital Image Processing
Digital Image Fundamental
• Eye Physiology:
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Digital Image Processing
Digital Image Fundamental
• Optical Sensors in retina: – Cones: Highly Sensitive to Color (6-7)×106
– Rods: Highly Sensitive to Low Levels of Illumination (75-150) ×106
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Digital Image Processing
Digital Image Fundamental
• Image Formation in the Eye:
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Digital Image Processing
Digital Image Fundamental
• Brightness Adaptation:
– Eyes can adapts a large dynamic ranges of intensity (1010) But NOT Simultaneously.
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Digital Image Processing
Digital Image Fundamental
• Brightness Discrimination:
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Digital Image Processing
Digital Image Fundamental
• Weber Ratio:
CΔI =Increment of illumination discriminable 50% times
Rods
Cons
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Digital Image Processing
Digital Image Fundamental
• Match Band Effect:
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Digital Image Processing
Digital Image Fundamental
• Simultaneous Contrast:
Appear Darker
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Digital Image Processing
Digital Image Fundamental
• Eye illusions:
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Digital Image Processing
Digital Image Fundamental
• 2.2: Light and the Electromagnetic Spectrum
• 2.3: Image Sensing and Acquisition
• Ignored!
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Digital Image Processing
Digital Image Fundamental
• A Simple Image Formation:
• Gray Level :Intensity of monochrome images.
, , ,
0 , : Illumination
0 , 1: Reflection
f x y i x y r x y
i x y
r x y
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Digital Image Processing
Digital Image Fundamental
• Image Sampling and Quantization (1):
Scan Line
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Digital Image Processing
Digital Image Fundamental
• Image Sampling and Quantization (2):
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Digital Image Processing
Digital Image Fundamental
• Image Sampling and Quantization:
– Spatial and Gray Level Resolution
– How to determine the sampling rate?
– Nyquist sampling theorem • If input is a band-limited signal with maximum frequency ΩN
• The input can be uniquely determined if sampling rate ΩS > 2ΩN
– Nyquist frequency : ΩN
– Nyquist rate : ΩS
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Digital Image Processing
Digital Image Fundamental
• Digital Image Representation:
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Digital Image Processing
Digital Image Fundamental
• Digital Image, Mathematical Definition:
– I = f(x,y)
– I: intensity (or color)
– (x,y): Position or Coordination
– When (x,y) and I are finite and discrete quantities -→ digital image
– pixels, picture elements, image elements
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Digital Image Processing
Digital Image Fundamental
• Mathematical Representation:
bits to store the image = M x N x k gray level = L = 2k
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Digital Image Processing
Digital Image Fundamental
• L- level digital image of size M×N
– Means: A digital image having: • A spatial resolution M×N pixels
• A gray-level resolution of L levels (0 … L-1)
• Spatial resolution in real-world space
line width=W cm space width=W cm
Resolution = 1/2W (line/cm)
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Digital Image Processing
Digital Image Fundamental
• L = 2k gray levels, gray scales [0,…,L-1]
• The dynamic range of an image
– [min(image) max(image)]
– If the dynamic range of an image spans a significant portion of the gray scale → high contrast
– Otherwise, low dynamic range results in a washed out gray look.
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Digital Image Processing
Digital Image Fundamental
• Saturation and Noise:
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Digital Image Processing
Digital Image Fundamental
• Number of Storage bits (M=N):
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Digital Image Processing
Digital Image Fundamental
• Spatial and Intensity Resolution:
1250 dpi 300 dpi 150 dpi 75 dpi
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Digital Image Processing
Digital Image Fundamental
• Bits Reduction (More Quantization):
– 8 bits to 1 bits (Left to Right-Top to Down)
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Digital Image Processing
Digital Image Fundamental
• Three types of image (Low/Medium/High Details):
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Digital Image Processing
Digital Image Fundamental
• Sampling-Quantization Tradeoff:
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Digital Image Processing
Digital Image Fundamental
• Image Interpolation: – Nearest Neighbor (NN)
– Bilinear (BL) using 4 nearest neighbor:
– Bicubic (BC) using 16 nearest neighbor:
– …
,f x y ax by cxy d
3 3
0 0
, i j
ij
i j
f x y a x y
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Digital Image Processing
Digital Image Fundamental
• Image Interpolation (Example): – Reduced to 72 dpi
– NN, BL, BC
– Reduced to 150 dpi
– NN, BL, BC
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Digital Image Processing
Digital Image Fundamental
• Basic Relationships Between Pixels:
– 4-Neighbors
– Diagonal Neighbors
– 8-Neighbors:
4 : 1, , 1, , , 1 , , 1N p x y x y x y x y
: 1, 1 , 1, 1 , 1, 1 , 1, 1DN p x y x y x y x y
8 4: DN p N p N p
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Digital Image Processing
Digital Image Fundamental
• Basic Relationships Between Pixels:
4 8
1 1 1 1 1 1
1 1 1 1
1 1 1
1
0 0 0
0 0
0
1
0 0
1
1 1 1
DN N N
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Digital Image Processing
Digital Image Fundamental
• Adjacency:
– p and q are 4-adjacent:
– p and q are 8-adjacent:
– p and q are m-adjacent:
4q N p
8q N p
4 4 4Dq N p or q N p and N p N q
8 m
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Digital Image Processing
Digital Image Fundamental
• Distance Measure:
• Examples:
– Euclidean:
– D4 (City Block or Manhattan):
– D8 (Chessboard):
a. D p,q 0 D p,q 0 iff
b. D p,q D q,p
b. D p,q D p,r D r,q
p q
2 2
,eD p q x s y t
4 ,D p q x s y t
8 , ,D p q Max x s y t
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Digital Image Processing
Digital Image Fundamental
• Constant Distance Contour:
– D4 (Left)
– D8 (Right)
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Digital Image Processing
Digital Image Fundamental
Mathematical Tools:
– Array and Matrix Operations
– Linear and nonlinear Operation • Fourier Filtering, Ordered Statistics Filtering, …