Elements of Visual Perception

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Elements of Visual Perception

• Dr. Jiajun Wang
• School of Electronics Information Engineering
• Soochow University

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Elements of Visual Perception
Outline

• Structure of the human eye
• Image formation in the human eye
• Brightness adaptation and discrimination

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Elements of Visual Perception
Structure of the human eye

• The cornea and sclera outer cover
• The choroid
• Ciliary body
• Iris diaphragm
• Lens
• The retina (two kinds of receptors)
• Cones vision (photopic/bright-light vision)
  centered at fovea, highly sensitive to color
• Rods (scotopic/dim-light vision) general view
• Blind spot

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Elements of Visual Perception
Structure of the human eye
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Elements of Visual Perception
Structure of the human eye
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Elements of Visual Perception
Image formation in the human eye

• Flexible lens the principle difference from an
  ordinary optical lens.
• Controlled by the tension in the fibers of the
  ciliary body
• To focus on distant objects flattened
• To focus on objects near eye thicker
• Near-sighted and far-sighted

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Elements of Visual Perception
Image formation in the human eye
Radiant Energy
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Elements of Visual Perception
Brightness adaptation

• Dynamic range of human visual system 10-6104 mL
  (millilambert)
• Can not accomplish this range simultaneously
• The current sensitivity level of the visual
  system is called brightness adaptation level

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Elements of Visual Perception
Brightness adaptation
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Elements of Visual Perception
Brightness discrimination

• Weber ratio (the experiment)
• I the background illumination
• the increment of illumination
• Small Weber ratio indicates good discrimination
• Larger Weber ratio indicates poor discrimination

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Elements of Visual Perception
Brightness discrimination
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Elements of Visual Perception
Psycho-visual effects

• The perceived brightness is not a simple function
  of intensity
• Mach band pattern
• Simultaneous contrast
• Optical illusion

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Elements of Visual Perception
Mach band pattern
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Elements of Visual Perception
Simultaneous contrast
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Elements of Visual Perception
Optical illusion
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Elements of Visual Perception
Optical illusion
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Elements of Visual Perception
Optical illusion
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Sampling, Quantization and Other Simple Operations

• Dr. Jiajun Wang
• School of Electronics Information Engineering
• Soochow University

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Sampling, Quantization, and Operations
Outline

• Image formation model
• Uniform sampling
• Uniform quantization
• Digital image representation
• Relationships between pixels
• Arithmetic operations
• Logical operations

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Sampling, Quantization and Other Simple Operations
Image Formation Model
may be characterized by two components
Monochrome image
Illumination
Reflectance
Typical values of the illumination and
reflectance
Illumination sun on earth 90,000 lm/m2 on a
sunny day 10,000 lm/m2 on a cloud day moon on
clear evening 0.1 lm/m2 in a commercial office
is about 1000 lm/m2
Reflectance 0.01 for black velvet, 0.65 for
stainless steel, 0.80 for flat-white wall paint,
0.90 for silver-plated metal, and 0.93 for snow
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Sampling, Quantization, and Operations
Uniform sampling and quantization

• Sampling
• digitalized in spatial domain
• Quantization
• digitalized in amplitude

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Sampling, Quantization, and Operations
Uniform sampling and quantization
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Sampling, Quantization, and Operations
Digital image representation
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Sampling, Quantization, and Operations
Image resolution

• Spatial resolution the more pixels in a fixed
  range, the higher the resolution
• Gray-level resolution the more bits, the higher
  the resolution

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Sampling, Quantization, and Operations
Image zooming and shrinking

• Both applied to digital image
• Zooming
• Creation of new pixel locations
• Assignment of gray levels to those new locations
• Pixel replication, when increasing the size of an
  image an integer times
• Nearest neighbor interpolation
• Bilinear interpolation
• Bicubic interpolation
• Shrinking

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Sampling, Quantization, and Operations
Bilinear Interpolation
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Sampling, Quantization, and Operations
Relationships between pixels

• Neighbors of a pixel
• 4-neighbors
• diagonal-neighbors
• 8-neighbors
• Adjacency
• 4-adjacency
• 8-adjacency
• m-adjacency

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Sampling, Quantization, and Operations
Relationships between pixels

• m-adjacency

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Sampling, Quantization, and Operations
Relationships between pixels

• Path 4, 8, and m-paths
• A sequence of distinct pixels from pixel p to q.
• Connectivity
• Connect set only has one connected component.
• Region
• Region is a connected set.
• Boundary
• The set of pixels in the region which has one or
  more neighbors that are not in the region.

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Sampling, Quantization, and Operations
Arithmetic operations

• Addition
• Subtraction
• Multiplication
• Division

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Sampling, Quantization, and Operations
Logical operations

• AND
• OR
• Complement (NOT)
• XOR