sborník

Henryk Gliński
distortion coefficients requires fairly complex calculations. In the author’s
opinion, it is purposeful to separate the elements and determine the
distortion center first on the basis of the photographs of a specially prepared
pattern and then, on the basis of the photographs of another pattern, the
distortion coefficients.
2 Distortion center determination
The method suggested by the author is based on the remark that the straight
lines passing through the distortion center are not deformed. Thus, if a
bundle of parallel straight lines is photographed, then the one with least
deformed picture shall pass nearest the distortion center.
3 Practical determination of the distortion center
A pattern consisting of 25 straight lines, each 200 cm long and 0.5 cm
distance between each line, was prepared and printed. The pattern was
placed along the diagonal. In total, 20 photographs were taken – 10 along
each diagonal. From each photograph recorded in the RAW format, only the
luminance component (green) was used, in order to avoid the chromatic
distortion. Then, using the generally known algorithms, the pictures of the
straight lines were recognized by converting them into sequences of points.
Figure 1. The pattern for determination of the distortion center
For each sequence of points the correlation coefficient was calculated
and the equation coefficients of the straight line approximating a given
sequence of points. A sequence of points with the highest correlation
coefficient was selected from each photograph. Photograph 2 presents the
location of the straight lines approximating the selected sequences. Based
on the statistical calculations, considering the correlation coefficients, an
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