Segmentation d'images couleur par un opérateur gradient vectoriel ...
Segmentation d'images couleur par un opérateur gradient vectoriel ...
Segmentation d'images couleur par un opérateur gradient vectoriel ...
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QUANTIFICATION ET MORPHOLOGIE DE PHASES DE CLINKER PAR ANALYSE D'IMAGE.<br />
The contrast of the phases depends on the pre<strong>par</strong>ation of the sample. To saturate the<br />
pores of the clinker, it has to be embedded with epoxy resin in a vacuum, and after hardening,<br />
the pre<strong>par</strong>ation is polished. To make the following etching as regular as possible, the surface<br />
should be scratch-free and without any relief. Different etching methods can be used for the<br />
visual microscopic examination. For the human visual system, coloration is only one of many<br />
<strong>par</strong>ameters in the crystal identification, but for image processing, a regular coloration is<br />
presupposed. Therefore, etching should fulfil the following requirements:<br />
• The coloration of the different phases must be as homogeneous as possible. The<br />
crystals of the same phase should be coloured equally. The colour should be<br />
homogeneous within a crystal.<br />
• The etching must be repeatable.<br />
• The etching should make the inner structure of the crystals visible (texture in the<br />
belite).<br />
The upper requirements are fulfilled with a combination of HNO3 and NH4Cl. This<br />
method is preferred to the etching via HF vapour, which is used in other studies [Märten et al.,<br />
1994 ; Theisen, 1997]. The first ones are easier to use and less dangerous. They colour alite blue,<br />
belite brown and emphases the laminar structure of the belite. Little variations in the hue of<br />
certain crystal and in the internal coloration of the crystal can be accepted. Image processing can<br />
be adapted to these tolerances. The proposed system is optimised to a clinker, which is pre<strong>par</strong>ed<br />
as described.<br />
2.3 IMAGING SYSTEM<br />
Automatic image processing is based on digital images. The transition from the<br />
microscope to the computer is made in two steps. Firstly, the microscopic image is changed in an<br />
electric signal by a video camera. Current CCD colour cameras (SONY DXC-C1MDP) produce<br />
images with high resolution. The video signal can be visualised with a TV-screen or it can be<br />
digitised by a PC-digitiser-board (MATROX Meteor frame grabber) which forms a digital image<br />
from the input signal. The colour information in the video signal is divided in the three<br />
components: red, green and blue (RGB). Each component is se<strong>par</strong>ately digitised, allowing the<br />
representation of the true colours of the clinker on the PC-screen.<br />
The well-focused image can be saved and the system is ready for the next image. The<br />
operator can store a great number of images for the same clinker sample in a very short time.<br />
These images are then processed on a standard PC that easily provides the possibility to store the<br />
colour images and print them out.<br />
2.4 IMAGE CHARACTERISTICS<br />
The digitiser divides the image in 768*576 picture elements (PAL-format). By using a<br />
magnification factor of the microscope as the point co<strong>un</strong>ting uses it, a resolution of<br />
WORLD CEMENT RESEARCH AND DEVELOPMENT 1998 97