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Dr. Chittaranjan Verma delivered this lecture for Digital Image Processing course at B R Ambedkar National Institute of Technology. It includes: Motivation, Digital, Image, Processing, Storage, Standard, Definition, Frame, Rate
Typology: Slides
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Image size = 720 x 480 pixels
Frame rate = 30 fps (frame per seconds)
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11
3
Transmission: Broadcast TV, remote sensing via satellite,military
communications
via
aircraft,
radar
and
sonar,
teleconferencing, computer communications, facsimile, …
Storage:
Educational
and
business
documents,
medical
images (CT, MRI and digital radiology), motion pictures,satellite images, weather maps, geological surveys, ...
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6
Compression Ratio (
)
b
C
b
of the first dataset b
if b = b’, C = 1 and R = 0, relative to the second data set, thefirst set contains no redundant data
if b >> b’, C
∞
and R
1, relative to the second data set,
the first set contains highly redundant data
if b << b’, C
0 and R
∞
, relative to the second data set,
the first set is highly compressed
C = 10 means 90% of the data in the first data set is redundant
8
A system of symbols (letters, numbers, bits, etc.) used torepresent a body of information
Code word:
Each piece of information is assigned a sequence of code
symbols
Code length: The number of symbols in each code word
A natural m-bit coding method assigns m-bit to each graylevel without considering the probability that gray level occurs
very likely to contain coding redundancy
Basic concept
Utilize
the
probability
of
occurrence
of
each
gray
level
(histogram)
to
determine
length
of
code
representing
that
particular gray level:
variable-length coding
Assign shorter code words to the gray levels that occur mostfrequently or vice versa
9
M
x
N
pixel
image is
MNL
avg
For a natural m-bit coding
L
avg
= m
Let 0
1: Gray levels (discrete random variable)
) :Propability of occurrence of
:Frequency of gray level:Total number of pixels in the image :Total number of gray level
) :Number of bits
k
r
k
k
k
k
k
r
p
r
r
n
r
n L
l r
(^10)
used to represent
:Average length of code words assigned to gray leve
ls
k
L
k
avg
k
r
k
r
k
k
avg
n
l r
p
r
where p
r
k
n
r
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11
Image features
All 256 gray levels are equallyprobable
uniform histogram
(variable length coding can notbe applied)
The gray levels of each lineare selected randomly sopixels are independent of oneanother in vertical direction
Pixels along each line areidentical, they are completelydependent on one another inhorizontal direction
A computer generated(synthetic) 8-bit image
M = N = 256
Spatial redundancy
12
Start of new intensity
Number of consecutive pixels having that intensity
(consider the image shown in previous slide)
Each 256 pixel line of the original image is replaced by a single8-bit intensity value
Length of consecutive pixels having the same intensity = 256
Compression Ratio =
14
The eye does not respond with equalsensitivity to all visual information
Certain
information
has
less
relative
importance
than
other
information
in
normal
visual
processing
psychovisually
redundant
(which
can
be
eliminated
without
significantly
impairing
the
quality
of
image
perception)
The
elimination
of
psychovisually
redundant
data
results
in
a
loss
of
quantitative
information
lossy data
compression method
A computer generated(synthetic) 8-bit image
M = N = 256
This image appears
homogeneous so we
can use its mean value
to encode this image
15
Image
compression
methods
based
on
the
elimination
of
psychovisually redundant data (usually called quantization) areusually
applied
to
commercial
broadcast
TV
and
similar
applications for human visualizationQuantization: Mapping a broad range of input values to a limitednumber of output values
Computer generated
(synthetic) 8-bit image
M = N = 256
Histogram of
the image
Result of
histogram
equalization
17
The
base
of
logarithm
determine
the
unit
used
to
measure
the
information.
If
base
is
selected
the
resulting unit of information is bit (binary). Similarly, form-base log the unit is m-ary
Example: Flipping a coin and communicating the result P(E)
= 0.5 (either head or tale)
= - log
2
= 1 bit
i.e. 1 bit is the amount of information conveyed whenone of the two possible equally likely events occurs
