110 Prakt. Met. Sonderband 38 (2006) 
pre-processing (11,6+0,6%) and with edge enhancement (11,7+0,6%), use of the high 
pass filter resulted in rather low values (11,0£0,6%). 
ı ZZ 
LS 
Frc 
pro 
ma 
por 
pro 
ed 
res 
pot 
7:2 
0.8 
Fig. 2: 200x micrograph as in Fig. 1 after high pass filter: steeper gradual change from dark to bright colours 
at the boundary of pore phase and matrix phase 
By 
im: 
mae 
shc 
nui 
est 
hig 
qu 
Fig. 3: 200x micrograph as in Fig. 1 after noise reduction and edge enhancement: well defined boundary of 
pore phase and matrix phase