MeanVarMatrixRing
Declaration: 
MeanVarMatrixRing (Data: TDouble2DArray; CentX, CentY, Rad1, Rad2: integer; var Mean, Variance: double): integer; 
Calculates the mean and the variance of the data contained in the twodimensional array Data, using all values in the annular region defined by its center [CentX,CentY] and the inner and outer radius given by the parameters Rad1 and Rad2 (the center coordinates and the radii are in pixels, the array Data has 0based indices).
The function returns the following error codes:
0 ... everything is OK
1 ... CentX and/or CentY are out of range
2 ... one of the radii is too low or negative

Hint: 
In order to calculate the mean and the variance in a circular region, set Rad1 to a zero value. 
