€ discernible, 
'egetation are 
  
zation 
rsion 
re 3d) linear 
ing serves as 
wes and the 
t which the 
intensity changes sharply, giving in this way picture of the 
boundaries. 
  
  
Figure 3d. Gallikos river, Sobel operator 
Axios (figure 2, number 4) is an important interboundary river 
in northern Greece. Its estuaries in Thermaikos Gulf, form a 
large bird-foot delta (as defined by Zuidam et al, 1979) (figure 
4). 
  
Figure 4. Axios delta 
The area has been formed by a combination of fluvial processes 
with marine influences. Several fluvial features (as tributaries) 
as well low vegetation (tonal and textural differences) in the 
riverbed can be discerned in figure 4. Cultivated areas on the 
left and right side of the riverbed and linear forms of roads are 
also detectable. The river transports and deposits material at the 
estuaries, detectable from the changes of light to dark tones in 
the mouth of the river (Lillesand T.M, 1987). 
The application of point operations (figures 4a, 4b) substantially 
helps to the detection of the above. The areas of deposition in 
the sea have characteristic form. 
  
Figure 4a. Axios delta — histogram equalization 
  
Figure 4b. Axios delta — brightness inversion 
The application of local operations (figures 4c, 4d) enhances 
details as areas of low vegetation, cultivations, roads, riverbed 
boundaries and highlights the changes in image intensity 
detecting boundaries of similar regions.