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Figure 1 : Situation map 
Figure 2: Digitized aerial photography 
The studied area is a watershed (about 60 hectares) where the 
transition between the two poles is a gradual one. The study 
and the structural cartography (scale 1/1000) was? done by 
L.VEILLON (1984). The corresponding image is extracted from 
the I.G.N. aerial photography (scale 1/20 000 ). 
2.1 Proceeding 
1. The two poles of the transformation system are drawn 
from the given map. 
2. The aerial photography is digitized; then processed so that 
a partition is done . The principle of the processing is to 
associate thresholding and counting. 
3. The comparison is made, at first visually, between the two 
maps and the processed image. 
4. We simulate others resolutions, starting from 30 p. that is 
0.60 m on the ground until 480 p that is 9,60 m on the ground; 
we stopped when the partition on the image was no more valid. 
2.2 Results 
1. None of the 13 pedological morphological criteria used to 
depict the system and then to draw the map seem to have a 
particular response in terms of forest cover. 
Figure 4: Result of the Fig. 3 image counted with a scanning 
window. 
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2. The "podzol" curve, reflects the mean of 6 different criteria 
(its precision is about 10 m. on the ground); it is digitized and 
then registered on the numerical image: it shows (Fig. 2) that 
the domain of forest cover which is therefore defined, is 
heterogeneous: because of the grey values and because of the 
size of the crowns (between 2m. and 20m.). The image 
processing (Fig. 3 and Fig. 4 ) makes appear a domain which 
form can be compared to the one of the "podzol" domain. The 
limits of the two domains can't be superimposed; only shapes 
may be compared (Fig. 5).