Resmi N.G. Reference: Digital Image Processing Rafael C. Gonzalez Richard E. Woods
What is a digital image? An array of real or complex numbers represented by a
finite number of bits.
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What is digital image processing? Processing of a two dimensional image using a
computer. Digital processing of any two dimensional data for storage, transmission and machine perception.
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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. Middle-Level Inputs are images; Outputs are attributes extracted from images. Involves image segmentation (partitioning image into regions), classification or recognition of individual objects.
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High-Level Working with recognized objects as in image analysis. eg; automated analysis of text I. II. III. IV.
V.
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Acquiring image of area containing the text. Preprocessing Segmenting individual characters. Describing characters in a form suitable for computer processing. Recognizing the individual characters.
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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. Pictures were sent by submarine cable between London and New York. 5 distinct levels of grey.
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1929: Levels of grey increased to 15.
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1964: Pictures of moon transmitted by Ranger7 were
processed using computers to correct various types of image distortion.
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Applications of DIP Medical applications-to study X-ray images.
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Geographic Information Systems-to study pollution
patterns from aerial and satellite images.
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Astronomy
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Applications classified based on their sources of energy Electro-magnetic spectrum (gamma rays with highest
energy to radio waves with lowest energy)
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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.
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X-ray Imaging X-rays are generated using an X-ray tube(vacuum tube with a cathode and an anode).
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Imaging in Ultra Violet Band
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Imaging in Visible and Infrared Bands
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Remote sensing applications
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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) Synthetic Imaging Archaeology Physics Biology Defense Industry Machine perception
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Fundamental Steps in Digital Image Processing
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Image acquisition Involves preprocessing such as scaling
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Image Enhancement Brings out details that are obscured. Highlights certain features of interest in an image.
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Image Restoration Improves appearance of an image Based on mathematical or probabilistic models of
image degradation.
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Colour Image Processing Colour is used to extract features of interest in an
image.
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Wavelets and Multiresolution Processing Wavelets are used: for representing images in various degrees of resolution for data compression pyramidal representation
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Compression Reduces the storage required to save an image or
bandwidth required to transmit it.
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Morphological Processing Tools for extracting image components that are useful
in the representation and description of shape of image. eg; boundary extraction.
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Segmentation Partitions image into its constituent parts or objects.
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Representation and description Output of segmentation stage - Raw pixel data(either the
boundary of a region or the region as a whole).
Choosing a representation - one step in transforming raw
data into form suitable for computer processing.
Description(feature selection) deals with highlighting
features of interest.
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Object Recognition Assigning labels to objects based on its descriptors.
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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 the quantity that each pixel represents. Luminances of objects Absorption characteristics of body tissue Radar cross-section of target Temperature profile of a region
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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. 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.
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Knowledge Base
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Knowledge about the problem domain. Details regions of an image where information of
interest is known to be located. Advantage: limits the search. Controls the interaction between modules.
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Components of an Image Processing System
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Image Acquisition Two elements: Image sensors Digitizer Image sensor – Physical device that is sensitive to the energy radiated by the object we wish to image. Digitizer – Converts sensing device output to digital form.
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Specialized Image Processing Hardware High speed front end subsystem. Two elements: Digitizer Arithmetic and Logic Unit (ALU) ALU performs arithmetic and logical operations in parallel on entire images. eg; averaging images for noise reduction.
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Image Processing Software Consists of specialized modules that perform specific
tasks. User can write code utilizing these specialized modules.
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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 storage space. 3 categories: Short-trem (during processing) Online storage (for fast access) Archival (infrequent access, massive storage) 3/18/2012
