| Image
Processing Articles
Index |
 |
| Overview |
| The
histogram in the context
of image processing
is the operation by
which the occurrences
of each intensity
value in the image
is shown. Normally,
the histogram is a
graph showing the
number of pixels in
an image at each different
intensity value found
in that image. For
an 8-bit grayscale
image there are 256
different possible
intensities, and so
the histogram will
graphically display
256 numbers showing
the distribution of
pixels amongst those
grayscale values. |
|
| Normalized
Histogram |
| Normalized
histogram is the histogram
in which the no. of
pixels for each intensity
level is divided by
the total no. of pixels
in the image. Hence,
if the whole of the
image is of the same
color, e.g. a white
paper picture, then
its normalized histogram
contains only one
non-zero number, and
that is 1 for the
255th intensity level,
which is the intensity
level for the white
color. |
|
| Normalized
Histogram(i)=(Total
Number of Pixels of
Intensity i)/(Total
Number of Pixels) |
|
| General
Working |
| The
image is scanned in
a single pass and
a running count of
the number of pixels
found at each intensity
value is kept. This
is then used to construct
a suitable histogram.
This operation is
performed in a single
pass algorithm, surfing
each pixel once, and
increment the no.
of occurrences of
the specific intensity
level depending upon
the intensity of that
particular pixel. |
|
| Guidelines
for Use: |
| Following
is the histogram: |
 |
|
| obtained
by the application
of the histogram operation
of the following image: |
|
 |
|
| The
histogram graph is
spread over all the
intensity levels.
But if the image is
dark then the histogram
graph is denser near
the low intensity
region. And denser
in the high intensity
region, when the image
is the bright one. |
|
| Sample
Project |
|
| 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 specialty 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 interface designed
for the sample project
as: |
|
 |
|
| In
this project the histogram
is obtained by calculating
the no. of pixels
for each gray image
intensity level. Then
calculate the maximum
no. of pixels for
one intensity level.
Then divide each of
the 256 no. of pixels
one for each intensity
level by the maximum
no. of pixels by max
and multiply by 300.
Thus the maximum length
of an intensity level
in the image is 300. |
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Project Files
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|
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