Digital Image Processing
Lecture - 2
Fall-2019
SEECS, NUST
Instructor: Muhammad Aasim Rafique
Steps in DIP
Human Vision
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Iris
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Lens
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Retina
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Cones
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6-7 Million
Rods
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75-150 Million
Human Vision
Cones
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Located near fovea
Highly sensitive to color
Each cone is connected to single
nerve, so details are resolved
Muscles rotate eye to make an
image fall on fovea
Photopic or bright vision
Rods
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Distributed
Several rods connected to a single
nerve, reduces the amount of details
Sensitive to low level of illumination
Scotopic or dimlight vision
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Fixed distance between lens and retina
Vary the shape of lens to achieve proper
focus
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The range of focal length 14mm – 17mm
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e.g height of retinal image
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H/D = h/d, 2.55 mm
Brightness Adaptation
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Humans can adapt to enormous
light intensity levels
subjective brightness is a
logarithmic function of the light
intensity incident on the eye
visual system cannot operate
over such a range
simultaneously
accomplishes this large variation
by changing its overall sensitivity
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Brightness adaptation
Brightness discrimination
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ability of the eye to discriminate between changes in light intensity at any specific
adaptation level
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uniformly illuminated area large enough to occupy the entire field of view
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Delta Ic / I is Weber ratio
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typical observer can discern a total of one to two dozen different intensity changes
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eye is capable of a broader range of overall intensity discrimination
Mach Band
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brightness is not a simple function of intensity
Simultaneous Band
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a region’s perceived brightness does not depend only on
its intensity
Optical Illusion
EM Spectrum
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the range of colors we perceive in visible light is a small portion
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Expressed in terms of wavelength, frequency and Energy
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Lambda is wavelength, v is frequency, c is speed of light
EM Spectrum
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Energy of various components is given by, E = hv
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plank’s constant, h
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Visible band is 0.43 um to 0.79 um
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Light that voids color is called monochromatic
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Intensity, gray level, grayscale
Chromatic light
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Radiance: total amount of energy that flows from the light source
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Luminance: a measure of the amount of energy an observer
perceives from a light source
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Brightness
Image Sensing and Acquisition
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Illumination, Scene, Sense
Single Sensing Element
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Inexpensive
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Precise control
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Slow
Sensor Strips
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in-line sensor strip
Sensor Array
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individual sensing elements arranged in the form of a 2-D
array
Image Formation Model
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f(x,y) , scalar quantity, non negative
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0 <= f(x,y) < infinity
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Source illumination, I
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Reflection from the object, r
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f(x,y) = i(x,y) x r(x,y)
0 <= I < infinity
● 0(total absorption) <= r <= 1 (total reflectance)
● Reflectance can be replaced with transmissivity
Examples
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Clear day luminance 90,000 lm/m2
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Cloudy day, 10,000
Clear Evening, 0.01
Commercial office: 1000 lm/m2
Homework 1
Homework # 1
EE433- Fall 2019
It is important to know what you are learning and what will be the outcome of this learning. It is better to
know “what” and approach “How”?. This homework is about getting an intuition of “what”
We have discussed about the course Digital Image Processing (DIP). We had a brief introduction of it
applications with images.
You need to identify an application of DIP and write a two page summary of its usages, approaches
of DIP used in it. You dont need to understand the “How” part. Th focus should be on “what” part.
Submission details: Submit a soft copy
Deadline: 12th Sept. 2019
Note: No late day for this homework.
Thankyou
Questions?