[BV] Added variance function

Signed-off-by: Jim Martens <github@2martens.de>

bv/variance.m

@@ -0,0 +1,31 @@
+function [v] = variance( image )
+%VARIANCE Calculates the variance of an image
+
+    if isinteger(image) 
+        error(message('MATLAB:var:integerClass'));
+    end
+
+    % prepare some values needed for both mean and variance
+    n = 0;
+    mean = 0.0;
+    M2 = 0.0;
+    s = size(image);
+    rows = s(1);
+    cols = s(2);
+     
+    for x = 1:cols
+        for y = 1:rows
+            n = n + 1;
+            delta = image(y, x) - mean;
+            mean = mean + delta/n;
+            M2 = M2 + delta*(image(y,x) - mean);
+        end
+    end
+    
+    if n < 2
+        v = float('nan');
+    else
+        v = M2 / (n - 1);
+    end
+end
+