Image processing LECTURE 2-A
Transcript of Image processing LECTURE 2-A
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Digital Image Processing
ELE-4707
Lecture 2
Dr Hassan Ahmed
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Image Processing (Computer Vision) -Recap
Inverse Photography
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Stages in Computer Vision
Physics: Image Formation (Light,
Reflectance)
Physics: Cameras: Optics (Lens),
Sensors (CCD, CMOS)
Image Processing: Coding
(Transmission, Compression)
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Image Acquisition
Light is emitted by light source
Light is reflected from objects
Reflected light is sensed (captured) by eyeor by camera
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Type of illumination Incident light illumination: Camera and
light source are on the same side of theobject. The image shows the distribution
of the light intensity reflected by the object.
Transmitted light illumination: Camera
and light source are on opposite sides ofthe object. The screen shows the dark
form of the object in front of a light
background. Transmitted light illumination
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Type of Image capturing system
In everyday life a number of image
capturing systems are used,
depending on the application field.They differ in the acquisition principle
acquisition speed
spatial resolution sensor system
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the most-used sensors for capturing
images electronically are: area scan cameras
line scanners
laser scanners
nuclear magnetic resonance (NMR) tomographs
Thermo-graphic sensor systems (e.g. infrared cameras)
ultrasonic devices
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Classification of Sensors
Sensors can be categorized into the
following classes according to their
sensitivity ranges: Electromagnetic sensors - sensitive to a
certain range of electromagnetic radiation gamma radiation
X-ray radiation
the visual spectrum
the infrared spectrum
the radio wave range
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most important acquisition
method CCD cameras Single
imaging
sensor
Line sensor
Array Sensor
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CCD
The incoming light falls on a CCD (Charge
Coupled Device) sensor, which consists o
light-sensitive semi-conductor elements.
They can be arranged in a line (line
camera) or a matrix (area scan camera).
The number of electrons which are
collected is ro ortional to the li ht which
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Single sensor acquisition
Mechanical motion can be controlled with high precision, this
method is an inexpensive (but slow) way to obtain high-resolution
images.
Other similar mechanical arrangements use a flat bed, with the
sensor moving in two linear directions.
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Using Sensor Strip
Image acquisition through
linear sensor strip
Image acquisition through
circular sensor strip
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Sensor Arrays
Individual sensors can also be arranged
in the form of a 2-D array.
A number of electromagnetic and some
ultrasonic sensing devices frequently are
arranged in an array format.
Predominant arrangement found in digital
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Image Acquisition
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Image descriptionf(x,y):intensity/brightness of the image at
spatial coordinates (x,y)
0< f(x,y)
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The Digital Image Formation
The digital image is a numerical computer
representation of the physical image.The physicalimage is divided into small regions calledpicture
elements, orpixels. The number stored in eachpixel
represents the brightness of the scene in the designated
region.
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The Digital Image
The conversion process from physical to digital image is
called digitisation. At each pixel location, the
brightness of the physical image is sampled and
converted into an integer number, called the grey level.
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Sampling
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Quantisation
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Sampling and Quantization
Sampling and
quantization
Digital line scan
qua
ntization
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The Digital Image
The image displayed is stored as an array of numbers inthe computer memory.
Colour images are sampled 3 times, giving 3 digitalimages, 1 each for a primary colour variable (RGB, CMYor HSI).
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Digital ImageEachpixelhas an
address in the digitalimage, i.e. row or line
number and column or
sample number.
Typically, the origin
(x,y)=(0,0) is at the top-
left corner of the image.
A digital image of 640horizontal pixels and 400
vertical pixels will have
address values of x=0-
639 and y=0-399