Digital Image Processing Tutorial-Image Display
DIP- Image Display and Band Combination
In
the previous article of image processing, it is understood requirement of layer
stacking for a satellite image. Through layer stacking, satellite image, which
acquired/downloaded as individual bands can be displayed as true color
composite and false color composite. This article will help you to understand
about display a satellite image as well as process to make false color
composite through band combination.
Display Satellite Image in Erdas
After
layer stacking i.e. combined all bands in single layer, now color composite is
ready for display and analysis.
A viewer has
following menu…..
a. File
b. Utility
c. View
d. AOI
e. Raster
f. Vector
g. Help
The
File
menu in the viewer can be used to open an image and applying basic viewer functions.
If you move the cursor over the icons, you see a short indication of the
function in the lower left corner of the viewer.
b. Open
c. Raster Layer
d. Select drive to open the folder of satellite images.
e. Select the .img or .tiff file and
f. then click OK in the window.
To change Band combination in Erdas
Band combination can be changed by
Clicking Raster
option in Viewer
Click on band
combination from drop down menu bar
Change bands by selecting layer as in below red
circle
Now
it is important to understand the requirement of band combination. Satellite
images have reflectance value, which is stored in each pixel in the form of
digital number or value. This DN value
is recorded by sensor, which is reflected by earth surface feature and these
are recorded by sensor during the rotation around the earth. Sensors are
designed in such a way that they can record reflectance of different wave
length in different bands. This technology is very useful as it provide earth
surface pattern as per behavior with different portion of spectrum. One more
advantage, sensors can record reflectance in wavelength/band, which are not
visible to human eye such as infra-red and microwave.
This
band combination tool facilitates us to change band (which have reflectance
value recorded for a specific wave length). With this one can also make
visible, the wave length which is not visible to human eyes such as infra-red.
Through
this band combination, one can make true color composite and false color
composite. In remote sensing technology visible, infra-red and microwave length of
electromagnetic spectrum is used. In visible part of spectrum, blue, green and
red wave length is used where as in infra-red, near infra-red, shortwave
infra-red and thermal infra-red is used.
When
assign blue, green and red color to recorded blue, green and red wave lengths
respectively, than it is called True
color composite. Where as in false color composite, blue wave length is
skipped and near infra-red wave length is introduced. Now blue, green and red
color is assigned to green, red and near infra-red wave length respectively.
Such types of arrangement are called False
color composites.
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