A further possibility to define textural patterns after performing 
picture. preprocessing is the interpretation of the Fourier power 
DEN = spectrum /5/ of individual evaluation units (see fig. 5d). Ad- 
= vantage is hereby taken of the fact, that the radial and angular 
Ves. distribution of the values in the power spectrum is sensitive 
to the coarseness and directionality of the texture in the corres- 
lere ponding grey level distribution. Thus, a set of patterns can be 
a obtained by the evaluation of the averages AF (roc) of the power 
spectrum Ir (u, vJ* for ring and wedge shaped regions (eqn. (4)). 
3. 5a Uncertainties are given by the selection of appropriate inner 
lage, and outer radii (v? r,) lower and upper angle (x, o2); the 
iyed number of regions and the degree of overlapping between neigh- 
n boured regions. Errors can also be produced by the transformation 
3 algorithm itself. So it can be necessary to implement weight 
tri- functions to reduce errors caused by the different grey level 
tion distributions along the rim of the evaluation unit. These weight 
An functions again influence the Fourier power spectrum and, there- 
3 fore, the selected patterns, too. 
li- 
om 
lobal 
2 
sine AF, ifo M in ) = 7 | Flav) 
for- To (4) 
ural 
e and 
and 
ris alow | TET SH, 
     
id = Lan uw); dota tX,