Improvement of the curvature computation

The improvement of computing the the curvature of the digitized curves is presented. The standard scheme, i.e. computing curvature using convolution with the truncated Gaussian kernel, was studied. First, we show that systematic bias caused by curvature smoothing can be removed. Second, we demonstrate that large portion of the error has roots in other phenomena (i.e. anisotropy of the raster, limited size of the Gaussian, numerical integration of the convolution, and discretization).