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Bio-medical Ontologies Maintenance and Change Management

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126 L. Stanescu, D. Dan Burdescu, <strong>and</strong> M. Brezovan<br />

In ultrasound imaging the deformable models were successfully applied for<br />

segmentation of the echocardiograms, to detect the boundary of the fetus <strong>and</strong> the<br />

fetus head, or to outline the cysts in breast images. Though, the segmentation algorithms<br />

are limited in ultrasound images because of the high level of speckling present<br />

in this type of <strong>medical</strong> images [76].<br />

5.2 The Color Set Back-Projection Algorithm<br />

For detecting color regions, at Software Engineering Department Craiova, it was<br />

chosen the color set back-projection algorithm, introduced initially by Swain <strong>and</strong><br />

Ballard <strong>and</strong> then developed in the research projects at Columbia University, in the<br />

content-based visual retrieval domain [83, 86, 87]. This technique provides the<br />

automatic extraction of regions <strong>and</strong> the representation of their color content. The<br />

extraction system for color regions has four steps [83, 86, 87]:<br />

1. The image transformation, quantization <strong>and</strong> filtering (the transformation from<br />

the RGB color space to HSV color space <strong>and</strong> the quantization of the HSV color<br />

space at 166 colors)<br />

2. Back-projection of binary color sets<br />

3. The labeling of regions<br />

4. The extraction of the region features<br />

The algorithm reduces the insignificant color information <strong>and</strong> makes evident<br />

the significant color regions, followed by the generation, in automatic way, of the<br />

regions of a single color, of the two colors, of three colors.<br />

To conclude with, the second step of the color set back-projection algorithm is<br />

the following [83, 86, 87]:<br />

1. Detection of single color regions<br />

– Having the image histogram, H[m], all the values m ' = m for which<br />

H[ m]<br />

≥ p0<br />

are detected.<br />

– For each m' the color set c having the property c[ k]<br />

= 1for<br />

k = m <strong>and</strong><br />

c [ k]<br />

= 0 in other cases is found. On the image R[m,n] the back-projection<br />

algorithm for each color set c is applied <strong>and</strong> the color regions are found.<br />

For each region n the local histogram Ln [m] is stored.<br />

– The residue histogram [ m]<br />

= H [ m]<br />

− ∑ L [ m]<br />

is computed<br />

H r<br />

n n<br />

2. Detection of two colors regions<br />

– The values l '= 1 <strong>and</strong> m ' = m , l ≠ m , H[ 1]<br />

≥ p , 0 H[ m]<br />

≥ p <strong>and</strong> 0<br />

–<br />

H r[ 1]<br />

≥ p , 1 H r[ m]<br />

≥ p are found.<br />

1<br />

For each set l', m' the color set c having the property c [ k]<br />

= 1 for k = l'<br />

or<br />

k = m'<br />

<strong>and</strong> c[ k]<br />

= 0 in other cases is found. On the image R[m,n] the

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