===== Detect edges =====

{{:processing:edge_detect.jpg|}}

This function detects edges of objects using [[http://en.wikipedia.org/wiki/Canny_edge_detector|Canny algorithm]]. This algorithm is considered to be the best to detect edges on noisy images. The algorithm consists of:

  * Noise Reduction;
  * Gradient Calculation;
  * Non-Maximum Suppression which chooses only the points of gradient local maximum in the direction of gradient vector to be pixels of the edges;
  * Threshold Analysis and final selection of the edges.

In practice this algorithm works well with SPM images of rather big objects with distinct edges, for example, virus particles on mica surface:

{{:processing:edge_detect_1.jpg|}}

When the function is called up from [[меню_математика|Mathematics menu]] a setting window appears where threshold value and noise level must be specified as a fraction of 1.