peulernumberselection

Selects regions from Euler number.

Synopsis

peulernumberselection relation threshold [-m mask] [rg_in|-] [rg_out|-]

Description

peulernumberselection selects regions from their Euler number. The parameter relation specifies the order relation to the threshold value that is used to select or not a region.

The Euler number E for a region is defined as 1 - the amount of holes H in the region. Conversely, the amount of holes H can be determined from the Euler number: H = 1 - E.

The algorithm used to calculated the Euler number uses the local operation:
Let X(R) the number of the following 2x2 patterns (r region label for region R, et 0 other labels):

0 0
0 r

Let V(R) the number of the following 2x2 pattern

0 r
r r

then Euler(R) = X(R) - V(R)

Parameters

relation is an integer from [-3,3] which specifies the order relation to the threshold value:
- relation = 3: regions with the maximum value.
- relation = 2: regions >= threshold.
- relation = 1: regions > threshold.
- relation = 0: regions = threshold.
- relation = -1: regions < threshold.
- relation = -2: regions <= threshold.
- relation = -3: regions with the minimum value.
threshold is an integer. It corresponds to a Euler number.

Inputs

rg_in: a 2D region map.

Outputs

rg_out: a 2D region map.

Result

Returns the number of selected regions.

Examples

Selects regions with at least 2 holes (E=1-2=-1):

   peulerselection 2 -1 rin.pan rout.pan

C++ prototype

Errc PEulerNUmberSelection( const Reg2d &rg_in, Reg2d &rg_out, int relation, long threshold );

Version française

Sélection de régions sur leur valeur de nombre d'Euler.

Author: Régis Clouard