Properties of PCA can be used for determination of selected object orientation or its rotation,
too [2, 4]. Various method of image segmentation to object definition (like thresholding, edge
detection or others) must be used at first. Binary image containing object boundary or its area
in black (or white) pixels on the inverse background results from this process. After that two
vectors a and b containing the cartesian x and y coordinates of object’s pixels can be simply
formed. The vector x in the Eq. (1) is in this case a 2-dimensional vector consisting of a and
b respectively. The mean vector mx and the covariance matrix Cx are computed as well as its
eigenvector e. Its two elements - vectors e1 and e2 enable the evaluation of object rotation in
the cartesian axis or object rotation around the center given by mx. Fig. 4 illustrates the PCA
use for the determination of selected object orientation. The object boundary was detected at
first by means of LoG filter in the original gray-level image. The original has been rotated by a