| Image
Processing Articles
Index |
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| Background |
| The
OR binary operation
takes two binary inputs
and outputs 0 only
when both the inputs
are 0 and if at least
one input is 1 then
it outputs 1. The
NOR binary operator
is the complete inverse
of the AND binary
operation. NOR outputs
1 when both the inputs
are 0, else it produces
0. The functionality
of OR and NOR are
clarified by the help
of the truth tables: |
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| OR
NOR |
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| Using
OR and NOR boolean
algebra allows you
to represent things
like: |
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| He
will be at home or
in office. |
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| Understanding
OR & NOR Mathematically: |
| The
ORing of two images
is carried out by
performing OR operation
to the corresponding
images of the two
images to produce
the output pixel value.
For instance, suppose
that we wish to AND
the integers 167 and
211 together using
8-bit integers. 167
is 10100111 in binary
and 255 is 11010011.
ORing these together
in bitwise fashion,
we have 11110111 in
binary or 247 in decimal. |
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| This
is not at all the
only implementation
of this of the logical
operators rather you
can implement the
logical ORing and
NORing using some
thresholding to transform
the digital image
data into the binary
format, or simply
by taking the 0 pixel
value as the logical
0 and the non-zero
pixel values as the
logical 1 value. |
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| General
Working |
| The
OR and NOR operations
are performed through
a single pass module
which during operation
passes through the
each pixel of each
image and calculates
the pixels of the
output image by doing
the respective operation
on the corresponding
pixels to calculate
the output pixels.
It is necessary to
have two images of
the identical size.
In the sample program,
if two images are
not identical in size,
then they are made
of the same size (
explained below).
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| Guidelines
for Use |
| We
can illustrate the
function of the OR
operator using |
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| and |
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| The
images show a scene
with two objects,
one of which was moved
between the exposures.
We can use OR to compute
the union of the images,
i.e. highlighting
all pixels which represent
an object either in
the first or in the
second image. First,
we threshold the images,
since the process
is simplified by use
binary input. If we
OR the resulting images
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| and |
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| we
obtain applying OR
operator on the image |
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| and
we obtain applying
NOR operator |
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| C#
Sample Program: |
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| The
algorithm is coded
in C# using unsafe
so the quality and
speed of the program
may not be affected.
The class BitmapData
is used to read and
process the pixels
in the image. This
is the speicality
of C# to provide such
a speed even on image
processing applications.
There is a set of
modules that are designed
to implement the algorithm.
The program expects
that the input images
are grayscaled. Then
it takes the BitmapData
objects of the two
input images. It determines
which image is bigger
in width as well as
in height. Then it
scales the smaller
image to acquire the
size of the bigger
image to make the
sizes of both the
images equal. Then
the algorithm calculates
the ORed image in
the single pass through
the image. The final
output is an image
showing the result
of the effect of OR
operator on the two
input images which
is then displayed
on the screen in the
down most picture
box. |
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