The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008 
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workflow of homomorphic filtering is showing in Figure 5. The 
function of filtering as follows (Formula 1). 
In transfer function H(u,v), r L <1.0 and r H > 1.0, £> 0 is the cut off 
frequency of highness filtering. For most digital aerial images, 
rp= 3, ^¿=0.5 and £>o=14. The section diagram of filtering is 
showing in figure 6, and figure 7 is the result of homomorphic 
filtering operation of figure 3. 
z(x,y) = \nf(x,y) 
H(u, v) = (r„ - y L )[1 - e- c(Z)2( “’ v)/D ° } ] + y l 0) 
r 0 (x ,y) = e r(x ’ y) 
A. light illumination in cent 
B. water lead hotspot C. sunshine caused top light 
Figure 2. Example of hotspot problems in aerial images 
Figure 3. Two images in left is digital aerial photo, the top of 
image is light, bottom of image is dark, the seam line between 
photos is clear in mosaic orthophoto 
Figure 4. Left is aerial photo, middle is the low frequency 
singles of image (result of low pass filtering), right is the high 
frequency singles of image (result of high pass filtering) 
g{x,y) 
Figure 5. The workflow of homomorphic filtering