  Hough transform is a popular low-level computer vision algorithm. Its
computationally effective modification, Fast Hough transform (FHT), makes use
of special subsets of image matrix to approximate geometric lines on it.
Because of their special structure, these subset are called dyadic patterns.
  In this paper various properties of dyadic patterns are investigated. Exact
upper bounds on approximation error are derived. In a simplest case, this error
proves to be equal to $\frac{1}{6} log(n)$ for $n \times n$ sized images, as
was conjectured previously by Goetz et al.
