pvariancemerging

Performs priority region merging based on variance criterion.

Synopsis

Description

pvariancemerging merges connected regions of the input image rg_in if the difference between the variance of the region is lower than the specified threshold.

Two regions are connected if there exits a link between the related nodes in the input graph gr_in.

The principle of the algorithm is as follows:

For each region of the input region map rg_in:
- if the difference between the criterion value of the two connected regions ≤ threshold
  then merge them into one region.

The algorithm uses the priority merging that consists in merging regions with the lower difference.

The output region map reg_out defines the new regions and the output graph gr_out defines the new relationship between regions.

The variance is calculated as follows:

    variance(R)= SUM((im_in[i] - mean(R))^2, i in R) / N

where im_in[i] are pixels of the region R, and N is the number of pixels of the region R.

Parameters

number specifies the number of allowed merging. If number = -1 then all possible merging are done.
threshold specifies the maximum difference allowed between two regions to decide to merge them. Values are from the gray scale of the input image.

Inputs

rg_in: a region map.
gr_in: a graph.
im_in: a grayscale image.

Outputs

rg_out: a region map.
gr_out: a graph.

Result

Returns the number of merging.

Examples

Merges regions yielded by a quadtree splitting process:

   puniformityquadtree 0.9 tangram.pan a.pan
   prg2gr a.pan b.pan
   pvariancemerging -1 45 a.pan b.pan tangram.pan c.pan d.pan

C++ prototype

Errc PVarianceMerging( const Reg2d &rg_in, Graph2d &gr_in, Img2duc &im_in, Reg2d &rg_out, Graph2d &gr_out, long number, float threshold );

Version française

Fusion prioritaire de régions selon le critère de la variance.

Author: Laurent Quesnel