phistothresholding

Performs multi-thresholding on image using histogram analysis.

Synopsis

phistothresholding length [im_in|-] [im_out|-]

Description

phistothresholding classifies the input image pixels into a small number of clusters according to their value. Every pixel p of the input image is assigned to a cluster identified by the related threshold value:

   if threshold[k-1]<im_out[p]<=threshold[k].
   then im_out[p]=threshold[k]

The last threshold is equal to 255.

The number of clusters and the value of the thresholds are determined from the histogram. Thresholds are located as regional maxima of the histogram. The maxima are searched in the space of length gray levels around the gray level i.

Notice: This operator can only work on grayscale image of bytes.

Parameters

length defined the length of the search space of the regional minima. It is defined in gray level unit. The greater is the length, the less there are thresholds. A typical value is 10.

Inputs

im_in: a grayscale image of bytes (Img2duc, Img3duc).

Outputs

im_out: a grayscale image of bytes (Img2duc, Img3duc).

Result

Returns the number of thresholds.

Examples

Segments the tangram pieces:

   phistothresholding 10 tangram.pan out.pan

C++ prototype

Errc PHistoThresholding( const Img2duc &im_in, Img2dsl &im_out, int length );

Version française

Multi-seuillage d'une image de niveaux de gris par une ligne de partage des eaux de son histogramme.

Author: Olivier Lezoray