pentropymerging

Performs priority region merging based on entropy criterion.

Synopsis

Description

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

Two regions are connected if there exists 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 entropy for a region is calculated as follows:

   entropy= - SUM { Pi * log₂(Pi) }

where Pi is the probability of pixel i. (Pi is computed from the normalized histogram.)

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. A typical value is 0.

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
   pentropymerging -1 -2 a.pan b.pan tangram.pan c.pan d.pan

C++ Prototype

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

Version française

Fusion prioritaire de régions selon le critère de l'entropie.

Author: Laurent Quesnel