*4.4. The Crack Area*

The crack area is a surface parameter and determines which area is occupied by cracks. This parameter is used in two versions, i.e., as an absolute value expressed, e.g., in mm2, and as a relative value in relation to the total area of the area under analysis, then often the crack area is given as a percentage value. Compared to the previously mentioned parameters, the crack area is more difficult to determine because it requires more complex digital image processing techniques.

Similarly as in the case of measuring the crack length, also in the case of the measurement of the crack area, Szel ˛ag [12–16,98,101,102] applied a modification consisting in the measurement of the area which is limited by the cracks.
