**3. Techniques for the Detection of Individual Cracks and the Whole Cracking Pattern**

The first studies concerning the analysis of the morphology of cracks in cement composites were more qualitative than quantitative. Cracks were analyzed by means of a visual evaluation. This introduced great inaccuracies because the study was contaminated with human factor. Small portable measuring microscopes were started to be used for more accurate measurements, which were mainly used to determine the crack opening width in reinforced concrete structures [53]. It was only the development of digital technologies that initiated the development of research methods for the cracks analysis, as the computer image analysis was used for this purpose. The main problem of methods based on the digital image analysis is still the correct detection of cracks on the material surface. The reason for this is mainly a weak contrast of cracks to the remaining surface of the material. In the case of cement composites, cracks are visible as black or dark grey, and the natural shade of this group of materials is similar to grey. In recent years there has been a great development of digital testing methods for analyzing single cracks as well as the whole cracking patterns. This section discusses the most frequently used and at the same time most popular image analysis techniques, used in the analysis of cracks in cement composites, from the simplest in application to advanced segmentation algorithms.
