image processing lecture 2-a

8/14/2019 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
http://en.wikipedia.org/wiki/Image:CCD_line_sensor.JPGhttp://en.wikipedia.org/wiki/Image:CCD_line_sensor.JPG


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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
http://en.wikipedia.org/wiki/Image:CCD.jpghttp://en.wikipedia.org/wiki/Image:CCD.jpghttp://en.wikipedia.org/wiki/Image:CCD.jpg


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08/12/09 15

Image Acquisition


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08/12/09 16

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

image processing lecture 2-a

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