The International Archives of the Photogrammetry, Remote Sensing andSpatial Information Sciences. Vol. XXXVII. Part B7. Beijing 2008 
1104 
Linear Stretch 
Equalization Stretch 
Ik-Orig (red) 
Ik-Shift (green) 
Ik-Str (blue) 
Ik-Orig (red) 
Ik-Str(green) 
Ik-Str-Shift (blue) 
Ik-Orig (red) 
Ik-Shift (green) 
Ik-Str (blue) 
Ik-Orig (red) 
Ik-Str(green) 
Ik-Str-Shift (blue) 
Figure 2. Comparison of quality difference between individual bands of the four testing images (Ik-Orig, Ik-Shift, Ik-Str, and Ik-Str- 
Shift) by overlaying the same band from different images in different colour and checking colour appearance in the overlaid images 
(colour indicating difference exists; no colour indicating no difference) 
2.2 Classification 
To prove that the four testing images have the same image 
quality for digital classification, the ISODATA clustering tool 
is selected to cluster the four images into the same number of 
clusters using exactly the same clustering parameters. The 
ISODATA clustering is selected, instead of any supervised 
classifiers, to avoid operator’s influence in the classification. 
All of the four spectral bands are used in the clustering. The 
images are clustered into 16 clusters. And, the maximum 
clustering iteration is 20. 
To precisely compare the 16 clusters classified from the four 
images, the clustering result from Ik-Orig is shown in Figure 
3.a, and the results from Ik-Shift, Ik-Str and Ik-Str-Shift are 
overlaid with that of Ik-Orig and displayed in Figure 3.b, 3.c