Elements of Visual Perception-Digital Image Processing-Lecture 02 Slides Slides-Electrical and Computer Engineering, Slides for Digital Image Processing. University of Alabama (AL)

Digital Image Processing

Description: Elements of Visual Perception, Visual Perception, Cross Section, Human Eye, Retinal Surface, Rods, Cones, Distribution, Receptors, Imaging, Sampling, Quantization, Spatial, Resolution, Reducing, Gray Levels, Pixels, Connectivity, Adjacencies, Paths, Connected Components, Labeling, Digital Image Processing, Lecture Slides, Dr D J Jackson, Department of Electrical and Computer Engineering, University of Alabama, United States of America.
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Dr. D. J. Jackson Lecture 2-1Electrical & Computer Engineering
Computer Vision &
Digital Image Processing
Dr. David Jeff Jackson
Electrical & Computer Engineering
The University of Alabama
Dr. D. J. Jackson Lecture 2-2Electrical & Computer Engineering
Elements of visual perception
Goal: help an observer interpret the content of an
image
Developing a basic understanding of the visual
process is important
Brief coverage of human visual perception follows
Emphasis on concepts that relate to subsequent material
Dr. D. J. Jackson Lecture 2-3Electrical & Computer Engineering
Cross section of the human eye
Eye characteristics
nearly spherical
approximately 20 mm in
diameter
three membranes
cornea (transparent) & sclera
(opaque) outer cover
choroid contains a network of
blood vessels, heavily
pigmented to reduce amount of
extraneous light entering the
eye. Also contains the iris
diaphragm (2-8 mm to allow
variable amount of light into the
eye)
retina is the inner most
membrane, objects are imaged
on the surface
Dr. D. J. Jackson Lecture 2-4Electrical & Computer Engineering
Retinal surface
Retinal surface is covered in discrete light receptors
Two classes
Cones
6-7 million located primarily near the center of the retina (the fovea)
highly sensitive to color
can resolve fine details because each is attached to a single nerve
ending
Cone vision is called photopic or bright-light vision
Rods
75-150 million distributed over the retinal surface
multiple rods connected to a single nerve ending
give a general overall picture of the field of illumination
not color sensitive but are sensitive to low levels of illumination
Rod vision is called scotopic or dim-light vision
Dr. D. J. Jackson Lecture 2-5Electrical & Computer Engineering
Distribution of rods and cones
Dr. D. J. Jackson Lecture 2-6Electrical & Computer Engineering
Distribution of receptors (continued)
Distribution is radially symmetric about the fovea
Absence of receptors in the blind spot (emergence of the
optic nerve)
Receptor density measured in degrees from the fovea (the
angle formed between the visual axis and a line extending
from the center of the lens to the retina)
Fovea:
circular indentation in the retina (approximately 1.5 mm in diameter)
density of cones in that area is approximately 150,000/mm2
basic ability of the eye to resolve detail is within the realm of
electronic imaging sensors
Dr. D. J. Jackson Lecture 2-7Electrical & Computer Engineering
Imaging in the eye
Variable thickness lens: thick for close focus, thin for distant
focus
Distance of focal center of the lens to the retina (14-17 mm)
Image of a 15m tree at 100m
15/100 = X/17 or approximately 2.55 mm
Image is almost entirely on the fovea
Dr. D. J. Jackson Lecture 2-8Electrical & Computer Engineering
A simple imaging model
An image is a 2-D light intensity function f(x,y)
As light is a form of energy
0 < f(x,y) <
f(x,y) may be expressed as the product of 2 components
f(x,y)=i(x,y)r(x,y)
i(x,y) is the illumination: 0 < i(x,y) <
Typical values: 9000 foot-candles sunny day, 100 office room, 0.01
moonlight
r(x,y) is the reflectance: 0 < r(x,y) < 1
r(x,y)=0 implies total absorption
r(x,y)=1 implies total reflectance
Typical values: 0.01 black velvet, 0.80 flat white paint, 0.93 snow
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