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Chapter 10 How Remote Sensing Works
When multiple bands of imagery are available, they can be combined
together to view the image in color, rather than grayscale. Displaying imagery in color requires three bands to be displayed simultaneously, each
shown in a separate color other than gray. This is simplifying the technical
aspects a bit, but a display monitor (like a computer screen) is equipped
with devices called color guns that can draw a pixel on the screen in varying degrees of red, green, and blue. If an 8-bit image was drawn using the
red color gun, the values of 0 to 255 would not be in a range of black, gray,
and white, but instead would be in a range of the darkest red, medium red,
and very bright red. The same goes for the blue and green color guns—each
gun would be able to display an image in its respective color on a range of
0 to 255.
A color composite can be generated by displaying the brightness values
of one band of imagery in the red gun, a second band of imagery in the green
gun, and a third band of imagery in the blue gun. Each pixel would then be
drawn using brightness values as the intensity of the displayed color. For instance, a pixel could be displayed using a value of 220 in the red gun, 128 in
the green gun, and 75 in the blue gun, and the resulting color shown on the
screen would be a combination of these three color intensities. By using the
three primary colors of red, green, and blue, and combining them to varying
degrees using the range of values from 0 to 255, many other colors can be created (using the 256 numbers in the 0–255 range, with three colors, there are
16,777,216 possible color combinations) to be displayed on the screen (see
Figure 10.9 for examples of color formation).
To create colors, different values can be assigned to the red, green, and
blue guns. Table 10.1 shows some examples of ways to combine values together to form other colors (keeping in mind that there are millions of possible
FIGURE 10.9 Colors that
can be formed by adding
different colors together
(left) and subtracting
different colors from each
other (right).
Yellow
White
Blue
Blue
Green
Cyan
Cyan
Black
Magenta
Magenta
Red
Yellow
Green
Red
color gun equipment
used to display a
color pixel on a screen
through the use of the
colors red, green, and
blue.
color composite an
image formed by
placing a band of
imagery into each of
the three color guns
(red, green, and blue)
to view a color image
rather than a grayscale
one.
Chapter 10 How Remote Sensing Works
When multiple bands of imagery are available, they can be combined
together to view the image in color, rather than grayscale. Displaying imagery in color requires three bands to be displayed simultaneously, each
shown in a separate color other than gray. This is simplifying the technical
aspects a bit, but a display monitor (like a computer screen) is equipped
with devices called color guns that can draw a pixel on the screen in varying degrees of red, green, and blue. If an 8-bit image was drawn using the
red color gun, the values of 0 to 255 would not be in a range of black, gray,
and white, but instead would be in a range of the darkest red, medium red,
and very bright red. The same goes for the blue and green color guns—each
gun would be able to display an image in its respective color on a range of
0 to 255.
A color composite can be generated by displaying the brightness values
of one band of imagery in the red gun, a second band of imagery in the green
gun, and a third band of imagery in the blue gun. Each pixel would then be
drawn using brightness values as the intensity of the displayed color. For instance, a pixel could be displayed using a value of 220 in the red gun, 128 in
the green gun, and 75 in the blue gun, and the resulting color shown on the
screen would be a combination of these three color intensities. By using the
three primary colors of red, green, and blue, and combining them to varying
degrees using the range of values from 0 to 255, many other colors can be created (using the 256 numbers in the 0–255 range, with three colors, there are
16,777,216 possible color combinations) to be displayed on the screen (see
Figure 10.9 for examples of color formation).
To create colors, different values can be assigned to the red, green, and
blue guns. Table 10.1 shows some examples of ways to combine values together to form other colors (keeping in mind that there are millions of possible
FIGURE 10.9 Colors that
can be formed by adding
different colors together
(left) and subtracting
different colors from each
other (right).
Yellow
White
Blue
Blue
Green
Cyan
Cyan
Black
Magenta
Magenta
Red
Yellow
Green
Red
color gun equipment
used to display a
color pixel on a screen
through the use of the
colors red, green, and
blue.
color composite an
image formed by
placing a band of
imagery into each of
the three color guns
(red, green, and blue)
to view a color image
rather than a grayscale
one.