ABSTRACT
Digital
image processing is not a new phenomenon; techniques for the manipulation,
correction and enhancement of digital images have been in practical use for
over 30 years and the underlying theoretical ideas have been around far
longer. The term image
processing refers to manipulation and analysis of two-dimensional pictures.
Digital image processing is processing of two-dimensional pictures by a digital
computer. A Digital image is an array of numbers represented by finite number
of bits .An image given in form is first digitized and stored as
two-dimensional matrices of binary digits in computer memory. This digitized
image can then be processed and/or displayed on a high-resolution monitor. Image-to-image
transformation, not explicit description building .Image processing is used to
control image sharpness, noise and color reproduction. It is also used to
maximize the information content of images and to compress data for economical
storage and rapid transmission. Image processing algorithms based on complex
statistical methods and artificial intelligence may be used to perform such
operations as automatic colour balancing, object and text recognition and image
enhancement and manipulation.
Interest
in digital image processing stems from two principle application areas:
1)
Improvement of pictorial information for human interpretation
2) Processing
of image data for storage, transmission and representation for autonomous
machine perception.
One
of the first applications of image processing techniques in the first category was
in improving digitized newspaper pictures sent by submarine cable between London
and New York .
Introduction of Bart lane cable picture transmission system in early 1920's
reduced the time required to transport the picture across the Atlantic from more
than a week to less than 3 hours. Specialized printing equipment coded pictures
for Cable transmission and reconstructed them at the receiving end .Some of the
initial problems in improving the visual quality of these early digital
pictures were related to selection of brightness levels. During this period
introduction of a system for developing a plate via light beams developed by
coded picture tape improved the reproduction process considerably .From that
time to until now the improvements on processing methods for translation of digital pictures are continued .
INTRODUCTION
Digital
image processing is not a new phenomenon; techniques for the manipulation,
correction and enhancement of digital images have been in practical use for
over 30 years and the underlying theoretical ideas have been around far
longer.The term image
processing refers to manipulation and analysis of two dimensional pictures.
Digital image processing is processing of two dimensional pictures by a digital
computer. A Digital image is an array of numbers represented by finite number
of bits .An image given in form is first digitized and stored as
two-dimensional matrices of binary digits in computer memory. This digitized
image can then be processed and/or displayed on a high-resolution monitor. Image-to-image
transformation, not explicit description building .Image processing is used to
control image sharpness, noise and colour reproduction. It is also used to
maximize the information content of images and to compress data for economical
storage and rapid transmission. Image processing algorithms based on complex
statistical methods and artificial intelligence may be used to perform such
operations as automatic colour balancing, object and text recognition and image
enhancement and manipulation.
Interest
in digital image processing stems from two principle application areas:
1)
Improvement of pictorial information for human interpretation
2) Processing
of image data for storage, transmission and representation for autonomous
machine perception.
One
of the first applications of image processing techniques in the first category was
in improving digitized newspaper pictures sent by submarine cable between Landon
and New York .
Introduction of Bart lane cable picture transmission system in early 1920s
reduced the time required to transport the picture across the Atlantic from more
than a week to less than 3hours.Specialized printing equipment coded pictures
for Cable transmission and reconstructed them at the receiving end .Some of the
initial problems in improving the visual quality of these early digital
pictures were related to selection of brightness levels. During this period
introduction of a system for developing a plate via light beams developed by
coded picture tape improved the reproduction process considerably .From that
time to until now the improvements on processing methods for translation of digital pictures are continued .
Image
understanding involves the most basic knowledge of images. It is the science of
automatically understanding, predicting and creating images from the
perspective of image sources. Image source characteristics include illuminant
spectral properties, object geometric properties; object reflectance’s and
surface characteristics as well as numerous other factors, such as ambient
lighting conditions. The essential technologies of the science include image
component modeling, image creation and data visualization. Scientists at Kodak
work to develop automated ways to detect various characteristics of objects in
a picture (indoor/outdoor, people, faces, trees, buildings, etc.) that may be
useful in future applications such have database management or automatic
creation of photo albums. Let’s say you are writing an e-mail note to family or
friends. You mention your recent vacation trip. Automatically several pictures
from this trip are inserted in the note. Or you are creating the annual
Christmas letter, and pictures related to the events described during the
previous year become automatically available for insertion in the document.
Making this happen requires a number of technologies to identify what's in each
picture, the location of the scene, the day it was taken, who is in the picture
and on and on. Kodak laboratories are working to deliver such technologies as:
Image segmentation, the ability to automatically identify meaningful regions in an image. Face detection and
feature finding Image similarity (Identifying scenes that are similar in
location) a picture's main subject Scene categorization (i.e., what type of
scene is it?)
Image representation basics
1) Continuous
versus discrete data: an image is a discrete function of 2 variables
Represented by a
2D array of brightness values f(x, y), one for each pixel (x, y), also
Called picture
element , pel, image element.
2) Raster scan:
the rectangular grid scanning pattern is known as a raster.
3) Digitizers:
convert an image into a numerical representation
4) Image
sampling: digitization of spatial coordinates, e.g., a 512 x 512 image
5) Gray-level
quantization: amplitude digitization, e.g., 256 gray levels
ELEMENTS OF IMAGE PROCESSING SYSTEMS
A. Image Acquisition
Two
elements are required to acquire digital images
1. SENSORS
Physical
device that is sensitive to a band in the electromagnetic energy spectrum such as x-ray, ultraviolet, visible or
infrared bands and that produces an electrical signal output proportional to
level of sensed.
2. Digitizer
A
physical device for converting electrical output of physical sensing device
into digital Form.
i.
Scanner
A
scanner, briefly, is a very skinny CCD chip that is physically dragged across
the document to be scanned. As the document is scanned, light is bounced off
the document, and reflected back to the CCD chip, which records the intensity,
and sent to the computer.
ii.
Video
cameras:
Conventional
analogue video cameras are connected to a PC with a frame grabber who performs
conversion of the analogue video signal to digital images. The size of these
images is typically 768 
572 pixels which
corresponds to 0.44 MB per band. These cameras are relatively cheap, and they
are well-suited for real-time applications; this is why they are used for
industrial and medical purposes. On the other hand, both their sensor size and
their resolution are restricted. Currently, really digital video cameras are
gaining increasing importance.
572 pixels which
corresponds to 0.44 MB per band. These cameras are relatively cheap, and they
are well-suited for real-time applications; this is why they are used for
industrial and medical purposes. On the other hand, both their sensor size and
their resolution are restricted. Currently, really digital video cameras are
gaining increasing importance.
iii.
Amateur
cameras with CCD sensors:
CCD
Sensors can be mounted in the image planes of conventional photographic
cameras. In addition, such cameras need a device for data storage, e.g. a
PCMCIA drive, Flash card, etc. They can then be used just like analogue
cameras, the advantage being that the images can be checked immediately after
they have been taken on a laptop PC, and bad photographs can be replaced by
better ones. The sensor size varies considerably between different sensor models:
A typical one-chip sensor may have about 2000 
3000 pixels which
correspond to 6 MB per grey scale image or to 18 MB for a true color image. The
format of these sensors is about 2.4 
1.6 cm2; thus, it
is still 33% smaller than a common small format analogue photograph. These
cameras can be used for architectural applications and basically for everything
that can be photographed because their handling is very flexible. However, in
order to achieve an economic operating cycle, camera objectives with small
focal lengths have to be used which enlarge the aperture angle but bring about
geometrical problems due to distortions. The latest achievement is a digital
aerial camera consisting of four CCD chips delivering four perspective images
which can be resample to one quasi-perspective digital image.
3000 pixels which
correspond to 6 MB per grey scale image or to 18 MB for a true color image. The
format of these sensors is about 2.4 1.6 cm2; thus, it
is still 33% smaller than a common small format analogue photograph. These
cameras can be used for architectural applications and basically for everything
that can be photographed because their handling is very flexible. However, in
order to achieve an economic operating cycle, camera objectives with small
focal lengths have to be used which enlarge the aperture angle but bring about
geometrical problems due to distortions. The latest achievement is a digital
aerial camera consisting of four CCD chips delivering four perspective images
which can be resample to one quasi-perspective digital image.
iv.
Analogue
metric cameras:
Photographs
taken by metric cameras correspond with high accuracy to central perspective
images. These cameras deliver analogue images which have to be scanned
off-line. They are used for high-precision applications or if the format of the
CCD sensors is too small for an economic operating cycle, which is especially
true for, e.g., mapping purposes. Even the digital aerial camera cited above is
not yet operational, and for high-precision applications, the resembling
process required for combining the four images is not appropriate. Scanning
off-line turns out to be a very time-consuming process, which is especially
true for aerial images: The format of aerial images is usually 23 
23 cm2, and due to
the high demands for accuracy, they have to be scanned with high resolution,
thus yielding an enormous amount of data.
23 cm2, and due to
the high demands for accuracy, they have to be scanned with high resolution,
thus yielding an enormous amount of data.
v.
CMOS Image
Sensors
The
new Complimentary Metal Oxide Semiconductor (CMOS) based replacement for
25-Year-old CCD technology is called “CMOS Image Sensor Technology”. It is an
integrated circuit technology for realizing electronic “film”. Unlike CCD
technology, which relies on specialized processes, CMOS Image Sensor uses
mainstream microelectronics fabrication processes to produce the sensor chips.
It is likely that CMOS
Image Sensors
will replace CCDs within next few years, offering significant advantages over
CCDs in cost, performance, power consumption and system size.
vi.
Cameras
A
CCD camera is used to replace conventional cameras that use photographic film.
The main difference: instead of a piece of film in the focal plane, we have the
CCD chip. The intensities are recorded as an array of electrons, converted to numbers,
and stored in computer, to be processed later.
vii.
X-ray
imaging system:
The
output of an x-ray source is directed at object and a medium sensitive to
x-rays is placed on the other side of object. The medium thus acquires an image
of materials (such As bones and tissues) having various degree of x-ray
absorption.
viii.
Micro densitometers:
In
this sensor, the image to be digitized is in the form of transparency (such as
film negatives) or photograph. This photograph or transparency is mounted on a
flat bed or a Wrapped around a drum .scanning is accomplished by focusing a
beam of light on the image and translating the or rotating the drum in relation
to beam. In case of transparencies, beam passes through transparency; in
photographs it is reflected from surface of image. In both cases beam is
focused on a photo detector and detector based on intensity of beam records
gray level at any point.
ix.
Vidicon
camera:
Operation
of vidicon camera is based on principle of photo conductivity .An image focused
on the tube surface produces a pattern of varying conductivity that matches
distribution of brightness in optical image. Independently, electron beam scans
the rear surface if target and produces a signal proportional to input
brightness pattern. A digital image is obtained by quantizing this signal.
x.
Solid state
arrays:
Solid
state arrays are composed of discrete silicon imaging elements called photo sites.
They have a voltage output proportional to intensity of incident light. They
are of
Two types:
a. Line Scan Sensors-
Line scan sensors consist of a row of photo
sites and produces a two dimensional image by relative motion between scene and
detector.
b. Area sensors-
An
area sensor composed of a matrix of photo sites and is therefore capable of capturing
an image in the same manner as vidicon tube . These are used in freezing
applications.
B. Storage
An
8 bit image of size 1024x1024 pixels
requires one million bytes of storage. Thus providing adequate storage is
usually a challenge in the design of image processing systems.
Digital storage for image processing
applications falls into three principles Categories:
1. Short term
storage: For use during processing
2. On line
storage: For relatively fast recall.
3. Archival
storage: For massive storage.
One method of providing short term storage is
computer memory. Another is frame buffers that store one or more images and can
be accessed rapidly, usually at rapid rates. It also includes zoom, pan and
scroll. In on line storage it takes form of magnetic disks. A more recent
technology called M.O. (Magneto
Optical) storage to achieve close to G-byte of storage on a 5 ¼ in. Archival
storage is characterized by massive storage requirements but infrequent need
for access .Magnetic tapes and optical disks are usual media for archival
application.
C. Processing
Processing of digital images involves procedures that
are usually expressed in algorithmic
form. Thus, with the execution of image acquisition and display, most image
processing functions can be implemented in software. The only reason for
specialized image processing hardware is the need for speed in some
applications or to overcome some fundamental computer limitation. In
particular, the principle imaging hardware being added to these computers
consist of a digitizer and Frame
buffer combination for image digitization & temporary
storage, a so called arithmetic/logic
unit(ALU) processor for performing
arithmetic/logic operations at
frame rates & one or more frame buffer for fast access to image data during processing.
A significant amount of basic image
processing software can now be obtained commercially. When combined with other
software for application such as spread sheets
& graphics, it provides an excellent starting point for the solution
of specific image processing problem.
Sophisticated display device & software for word processing & report
generation facilitate presentation at result.
D. Communication
Communication in digital image
processing primarily involves local
communication between image
processing system and remote communication
from one point to another,
typical in connection with transmission of image data. Hardware & software for local communication
are readily available for most computers. Most computer networks use
standard communication protocols.
Communication across vast distances
presents a more serious challenge it the intent is to communicate image data rather than
abstracted result. We know that image contain a significant amount of data. A
voice-grade telephone line can transmit at a
maximum rate of 9,600 bits per second. Thus, to transmit a 512x512, 8
bit image at this rate would require nearly five minutes. Wireless links using
intermediate stations, such as satellites are much faster but they also cost
considerably more. The point is that transmission trivial. In this case, data
compression & decompression techniques play a central role in addressing this
problem.
E. Display
The
displays used for image processing--particularly the display systems used with
computers--have a number of characteristics that help determine the quality of
the final image.
Interlacing
To
prevent the appearance of visual flicker at refresh rates below 60 images/s,
the display can be interlaced as described in Section 2.3. Standard interlace
for video systems is 2:1. Since interlacing is not necessary at refresh rates
above 60 images/s, an interlace of 1:1 is used with such systems. In other
words, lines are drawn in an ordinary sequential fashion: 1, 2, 3, 4…., N.
Refresh Rate
The refresh rate is defined as the
number of complete images that are written to the screen per second. For
standard video the refresh rate is fixed at the values given in Table 3, either
29.97 or 25 images/s. For computer displays the refresh rate can vary with
common values being 67 images/s and 75 images/s. At values above 60 images/s
visual flicker is negligible at virtually all illumination levels. Monochrome
or color TV monitors are principle
display devices used in modern image
processing systems. Monitors are driven
by outputs of a hardware image display module in the back plane of host
computer or as a part of the hardware associated with an image processor. The signals at the output of display
module can also be fed in to an image recording device that produces a hard
copy (slides, photographs or transparencies) of the image being viewed on the monitor screen. Other display
media include random access cathode ray tubes (CRTS) & printing devices.
Printing image display devices are useful primarily for low, resolution image
processing work. Common means of recording an image directly on paper include laser printers, heat sensitive paper
devices & ink-spray systems.
1) Digital image
processing
2) Fundamental
steps in digital image processing:
3) Image
representation and modeling
4) Image
enhancement
5) Image
restoration
6) Image
analysis and computer vision
7) Image reconstruction
8) Image data
compression
IMAGE RESTORATION
Digital image restoration system:
Image Analysis and Computer
vision:
Computer vision
system
IMAGE ANALYSIS TECHNIQUES
1)
Feature Extraction:
2)
Spatial Features
3)
Amplitude Features
4)
Shape Features
5)
Geometrical Features
6)
Segmentation of Image
7)
Classification and Understanding
8)
Contour Following
9)
Boundary Representation
10) Chain
Coding
11) Image
Reconstruction
12) Image
Data Compression
1)
Neighbours of pixel
2)
Connectivity
3)
Need of transform
4)
Image Enhancement
5)
Spatial domain method
6)
Frequency domain method
7)
Point processing method
8)
Image negatives
9)
Contrast stretching
10) Compression
stretching
11) Gray
level slicing
12) Image
subtraction
13) Filtering
Approach
14) Spatial
filtering
15) Frequency
domain filtering
1) Medical diagnostic imaging
2) Remote sensing via satellite
3) Defence
4) Document processing
5) Others
6) Image
representation and modelling
7) Image
formation in eye
8) Image
sampling and quantization
CONCLUSION
In this topic of
image processing we studied every aspect related to improvement of degraded
image , by using image enhancement , histogram processing ,contrast
stretching, image
negative etc. We
come to know that image processing is need for any type of investigation and
recognition.
No comments:
Post a Comment