Segmentation d'images couleur par un opérateur gradient vectoriel ...

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QUANTIFICATION ET MORPHOLOGIE DE PHASES DE CLINKER PAR ANALYSE D'IMAGE. level in the local structure). The following different feature families for the classification of alite and belite crystals are considered: • Histogram features which describe the grey-level distribution in the analysing window. • Features calculated on the neighbourhood matrix [Haralick et al., 1973] which measure in a limited neighbourhood the coarseness or busyness of a micro-texture. • Features calculated on the run lengths matrix [Galloway, 1975] which measure the length, the number and the distribution of the grey-level runs in the analysing window and allow detection of the degree of homogeneity or heterogeneity. • Cooccurrence features [Haralick et al., 1973], which describe the repetition of greylevel changes, measured for pairs of points in a typical distance and direction. Microtextures and the Macro-textures can be detected preserving the directionality of each texture. • Frequency features (repetition rate of a micro-texture) can be calculated by a frequency transformation (Fourier- or Cosine-transform [Liu et al., 1990]) of the image window. These features evaluate the distribution of the frequencies and the directionality of the texture. The six families group a huge number of characteristic features or parameters. Some of the parameters are correlated, others are redundant in the different groups and may be excluded. The parameter signature obtained in this way will be used for the classification of each window. Discriminating analysis [Rao, 1952] A combination of the features can be found by the Multivariable Discriminating Factorial Analysis (MDFA). It creates a synthetic index, which allows the best separation of the two textures (alite and belite). This index is a linear combination of the texture features and takes into account the whole information. The best results are obtained for a combination of six features. A larger number does not increase the classification result but only introduces noise to the analysis. The feature selection depends on the size of the window. The most discriminate feature is the entropy of the test-window. The MDFA is a statistical analysis and needs a huge learning database. As database, 30 images with about 3000 test-windows for the two kinds of crystals were chosen. Figure 44 shows the histogram of the synthetic texture index computed by the MDFA on the learning base. The distribution shows that the texture index is sufficiently different for the two textures alite and belite, enabling the classification of the majority of the observation-windows. Note that there is an uncertain zone in which the decision is not possible. This zone represents less than 30% of the total population. WORLD CEMENT RESEARCH AND DEVELOPMENT 1998 102
QUANTIFICATION ET MORPHOLOGIE DE PHASES DE CLINKER PAR ANALYSE D'IMAGE. Colour analysis Apart from the texture, the discrimination between alite and belite can be made by colour analysis. The belite colour is brown and the alite colour varies from dark blue to bright green. The coloration depends on the etching and the characteristics of the clinker. In a digital system, each colour is represented by three components like red, green and blue (RGB) or hue, saturation and intensity (HSI). The hue and the saturation represent in polar coordinate the chromatic plane of the colour space. The chromatic plane can also be divided in the two orthogonal coordinates C 1 , C 2 which allow the separation of alite and belite crystals (Figure 45). This colour plane includes only the coloration and not the intensity. In the RGB colour space, a separation is not possible due to the tiny difference between the colours. This is mainly due to the poor saturation of the clinker colours. Figure 45 shows the distribution of alite and belite points in the C 1 C 2 colour plane. Two distinguished zones clearly appear for the two crystal types. Figure 44. - Histogram of the texture index. Figure 45.- 2D-Histogram in the chromatic plane. WORLD CEMENT RESEARCH AND DEVELOPMENT 1998 103
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N° d’ordre 2001ISAL0062 Année 2
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TABLE DES MATIERES. 3. Gradient cou
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TABLE DES MATIERES. La cuisson et l
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INTRODUCTION GENERALE. Le Clinker e
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Chapitre 2 INTRODUCTION AU TRAITEME
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INTRODUCTION AU TRAITEMENT D'IMAGES
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Chapitre 3 GRADIENT COULEUR MULITEC
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GRADIENT COULEUR MULITECHELLE (GCM)
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Page 51 and 52: GRADIENT COULEUR MULITECHELLE (GCM)
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