Digital Image Processing Tutorial-Image Display

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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 or false color composite using multi band. This article will help 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.

a. Click on File
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 wavelength 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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