| Image
Processing Articles
Index |
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| What
is a Color Image? |
| It
is possible to construct
(almost) all visible
colors by combining
the three primary
colors red, green
and blue, because
the human eye has
only three different
color receptors, each
of them sensible to
one of the three colors.
Different combinations
in the stimulation
of the receptors enable
the human eye to distinguish
approximately 350000
colors. A RGB color
image is a multi-spectral
image with one band
for each color red,
green and blue, thus
producing a weighted
combination of the
three primary colors
for each pixel. |
|
| A
full 24-bit color
image contains one
8-bit value for each
color, thus being
able to display 16777216
different colors.
However, it is computationally
expensive and often
not necessary to use
the full 24-bit image
to store the color
for each pixel. Therefore,
the color for each
pixel is often encoded
in a single byte,
resulting in an 8-bit
color image. The process
of reducing the color
representation from
24-bits to 8-bits,
known as color quantization,
restricts the number
of possible colors
to 256. However, there
is normally no visible
difference between
a 24-color image and
the same image displayed
with 8 bits. An 8-bit
color images are based
on colormaps, which
are look-up tables
taking the 8-bit pixel
value as index and
providing an output
value for each color. |
|
| What
is a GrayScale Image? |
| A
grayscale (or graylevel)
image is simply one
in which the only
colors are shades
of gray. The reason
for differentiating
such images from any
other sort of color
image is that less
information needs
to be provided for
each pixel. In fact
a `gray' color is
one in which the red,
green and blue components
all have equal intensity
in RGB space, and
so it is only necessary
to specify a single
intensity value for
each pixel, as opposed
to the three intensities
needed to specify
each pixel in a full
color image. |
|
| Often,
the grayscale intensity
is stored as an 8-bit
integer giving 256
possible different
shades of gray from
black to white. If
the levels are evenly
spaced then the difference
between successive
graylevels is significantly
better than the graylevel
resolving power of
the human eye. |
|
| Grayscale
images are very common,
in part because much
of today's display
and image capture
hardware can only
support 8-bit images.
In addition, grayscale
images are entirely
sufficient for many
tasks and so there
is no need to use
more complicated and
harder-to-process
color images. |
|
| What
is meant by the Term
RGB |
|
| It
is a useful fact that
the huge variety of
colors that can be
perceived by humans
can all be produced
simply by adding together
appropriate amounts
of red, blue and green
colors. These colors
are known as the primary
colors. Thus in most
image processing applications,
colors are represented
by specifying separate
intensity values for
red, green and blue
components. This representation
is commonly referred
to as RGB. |
|
| The
primary color phenomenon
results from the fact
that humans have three
different sorts of
color receptors in
their retinas which
are each most sensitive
to different visible
light wavelengths. |
|
| The
primary colors used
in painting (red,
yellow and blue) are
different. When paints
are mixed, the `addition'
of a new color paint
actually subtracts
wavelengths from the
reflected visible
light. |
|
| Guidelines
for Use |
| To
illustrate Conversion
of Color Image to
Grayscale image, we
start with a simple
image containing some
distinct artificial
objects(specifically
text) |
|
| C#
Sample Program: |
 |
|
| Now
we apply Grayscale
conversion to the
image to convert it
to Grayscale image. |
|
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