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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004
regression on a neighbourhood of 16 by 16 pixels. The large
deviation spectrum was computed for each point of the image
by the box method over a 32 by 32 pixels window. The number
of quantization values of the fractal components was fixed to a
reasonable value to avoid a too long computing time. The
singularity spectrum values in each point are the input to a k-
means algorithm.
All the parameters of the LMS algorithm were fixed in an
empirical way. The choice of the sizes of the neighbourhood
and of the studying windows results from a compromise
between the processing time and the quality of the results.
However, the size of the neighbourhoods is strongly related to
the characteristic dimension of the objects that have to be
detected in the image. The automatic estimation of all these
parameters will be the subject of future work, so that the
segmentation algorithm will be completely automatic.
e
4. RESULTS AND COMMENTS
In order to appreciate the contribution of the LMS method, we
compare the results with those obtained by the grey-level co-
occurrence method (Haralick et al, 1973) and by the Laws
filters method (Laws, 1980). We use only six of Haralick
texture parameters: energy, entropy, dissimilarity, contrast,
homogeneity and the correlation. The Laws filters of size 5 are
used, then the energy measures used for the segmentation are
computed by averaging the output of the filters on a square
window of size 15. Then, for each method, the computed
parameters are used as input to the k-means algorithm.
We initially carried out tests on images of the brodatz set of
textural images, then on a very high spatial resolution image of
a forestry scene. The results obtained for each image are then
compared with those resulting from the analysis based on the
grey-level co-occurrence matrices. The results are compared by
means of percentage of good classification in the case of the
brodatz image, and qualitatively in the case of the satellite
image. A ground truth map of this region will be done in a
future work. This will enable the computation of classification
rates for the IKONOS image. This map will be realized by
image-interpretation.
4.1 The brodatz image
f
Figure 1. Image create
The brodatz set of textural images provides many images of
natural textures. Some of them are rather close to what can be
seen in our IKONOS image. That is why we chose them to try
out our algorithm. They are usually used in the field of the
textural analysis, and thus it is easy to compare the results
provided with those presented in other articles. We have created
an image of 500x500 pixels with 5 different textures from the
brodatz set of natural textures (D29, D93, D100, D9 and D4),
see Figure 1.
The results given by the three methods are presented in Figure
2, Figure 3 and Figure 4.
Le 55
Figure 4. The LMS method
We noticed that the LMS method gives more homogeneous and
compact segments and that the rate of classification is much
better. The Laws filters method is not efficient for thé central
texture because it is a very chaotic texture which can be easily
confused with the others. The grey level co-occurrence method
can not differentiate some of the classes and gives the worst
results.
Method used Classification
results (in 96)
LMS algorithm 81
Grey level co-occurrence 57
Laws filters 67
Table 1. Classification results on the brodatz image