diff --git a/Analyser/ImagingAnalyser.py b/Analyser/ImagingAnalyser.py
index 488e68c..e818fb2 100644
--- a/Analyser/ImagingAnalyser.py
+++ b/Analyser/ImagingAnalyser.py
@@ -208,12 +208,12 @@ class ImageAnalyser():
         :rtype: numpy array
         """
 
-        numerator = np.atleast_1d(imageBackground - imageDrak)
-        denominator = np.atleast_1d(imageAtom - imageDrak)
+        denominator = np.atleast_1d(imageBackground - imageDrak)
+        numerator = np.atleast_1d(imageAtom - imageDrak)
         
-        numerator[numerator == 0] = 1
         denominator[denominator == 0] = 1
-        imageOD = np.abs(np.divide(denominator, numerator)) 
+        numerator[numerator == 0] = 1
+        imageOD = np.abs(np.divide(numerator, denominator))
         imageOD= -np.log(imageOD)
 
         if len(imageOD) == 1: