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

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