digital image processing fundamentals

Resmi N.G.Reference: Digital Image Processing

Rafael C. GonzalezRichard E. Woods

What is a digital image?� An array of real or complex numbers represented by a

finite number of bits.

2CS 04 804B Image Processing - Module13/18/2012

What is digital image processing?

� Processing of a two dimensional image using acomputer.computer.

� Digital processing of any two dimensional data forstorage, transmission and machine perception.


Three Types of Processing� Low-Level

� Both inputs and outputs are images.� Involves primitive operations such as image

preprocessing to reduce noise, contrast enhancement,and image sharpening.and image sharpening.

� Middle-Level� Inputs are images; Outputs are attributes extracted from

images.� Involves image segmentation (partitioning image into

regions), classification or recognition of individualobjects.


� High-Level� Working with recognized objects as in image analysis.� eg; automated analysis of text

I. Acquiring image of area containing the text.II. PreprocessingII. PreprocessingIII. Segmenting individual characters.IV. Describing characters in a form suitable for computer

processing.V. Recognizing the individual characters.


Origin of Image Processing� One of the first applications of digital imaging was

in the newspaper industry.� Early 1920’s- Introduction of The Bartlane Cable

Picture Transmission system.Picture Transmission system.� Pictures were sent by submarine cable between

London and New York.� 5 distinct levels of grey.


� 1929: Levels of grey increased to 15.

3/18/2012 CS 04 804B Image Processing - Module1 7

� 1964: Pictures of moon transmitted by Ranger7 wereprocessed using computers to correct various types ofimage distortion.


Applications of DIP� Medical applications-to study X-ray images.


� Geographic Information Systems-to study pollution patterns from aerial and satellite images.


� Astronomy


Applications classified based on their sources of energy

� Electro-magnetic spectrum (gamma rays with highest energy to radio waves with lowest energy)


� Gamma-ray Imaging� Radioactive isotope emits positrons while it decays.� Gamma rays are given off when a positron hits an

electron.� These are detected and image is created.


� X-ray Imaging� X-rays are generated using an X-ray tube(vacuum tube

with a cathode and an anode).


� Imaging in Ultra Violet Band


� Imaging in Visible and Infrared Bands


� Remote sensing applications


Other areas of application� Microwave band – Radar (explores inaccessible region’s of

earth’s surface)� Radio band – in medicine(Magnetic Resonance Imaging)

and astronomy� Acoustic Imaging (mineral and oil exploration over land

and water)and water)� Synthetic Imaging� Archaeology� Physics� Biology� Defense� Industry� Machine perception


Fundamental Steps in Digital Image Processing


Image acquisition� Involves preprocessing such as scaling


Image Enhancement� Brings out details that are obscured.� Highlights certain features of interest in an image.


Image Restoration� Improves appearance of an image� Based on mathematical or probabilistic models of

image degradation.


Colour Image Processing

� Colour is used to extract features of interest in an image.


Wavelets and MultiresolutionProcessing

� Wavelets are used: � for representing images in various degrees of resolution� for data compression� for data compression� pyramidal representation


Compression� Reduces the storage required to save an image or

bandwidth required to transmit it.


Morphological Processing� Tools for extracting image components that are useful

in the representation and description of shape ofimage. eg; boundary extraction.


Segmentation

� Partitions image into its constituent parts or objects.


Representation and description

� Output of segmentation stage - Raw pixel data(either theboundary of a region or the region as a whole).

� Choosing a representation - one step in transforming raw� Choosing a representation - one step in transforming rawdata into form suitable for computer processing.

� Description(feature selection) deals with highlightingfeatures of interest.


Object Recognition� Assigning labels to objects based on its descriptors.


Image Representation� Each digital image consists of a finite number of

elements called picture elements or pixels.� Each pixel has a particular location and value.� Image representation concerns with charaterization of� Image representation concerns with charaterization of

the quantity that each pixel represents.� Luminances of objects� Absorption characteristics of body tissue� Radar cross-section of target� Temperature profile of a region


Definition for a Digital Image� Any two dimensional function that bears information

is considered an image.� An image is defined as a two-dimensional function

f(x,y), where x and y are spatial coordinates.f(x,y), where x and y are spatial coordinates.� Amplitude of ‘f ’ at any pair of coordinates (x,y) is

called intensity of image at that point.� When x, y and amplitude values of ‘f ’ are all finite,

discrete quantities, the image is called a digital image.


Knowledge Base


� Knowledge about the problem domain.� Details regions of an image where information of

interest is known to be located.� Advantage: limits the search.� Advantage: limits the search.� Controls the interaction between modules.


Components of an Image Processing System


Image Acquisition� Two elements:

� Image sensors� Digitizer

Image sensor – Physical device that is sensitive to theenergy radiated by the object we wish to image.

Digitizer – Converts sensing device output to digital form.


Specialized Image Processing Hardware

� High speed front end subsystem.� Two elements:

� Digitizer� Arithmetic and Logic Unit (ALU)� Arithmetic and Logic Unit (ALU)

ALU performs arithmetic and logical operations inparallel on entire images.

eg; averaging images for noise reduction.


Image Processing Software

� Consists of specialized modules that perform specific tasks.

� User can write code utilizing these specialized � User can write code utilizing these specialized modules.


Mass Storage� A must for image storage� Image of size 1024 x 1024 pixels in which intensity of

each pixel is an 8-bit quantity requires 1 MB of storagespace.

� 3 categories:� Short-trem (during processing)� Online storage (for fast access)� Archival (infrequent access, massive storage)


Short-term: � Computer memory� Frame buffers

Online: � Magnetic disks� Magnetic disks� Optical media

Archival: � Magnetic tapes� Optical disks


Image Displays

Hardcopy devices

� Color TV monitors

� Laser printers, cameras, heat-sensitive devices.


Hardcopy devices

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digital image processing fundamentals

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