diff --git a/radiomics/glcm.py b/radiomics/glcm.py
index 04986ad0..73115a5e 100644
--- a/radiomics/glcm.py
+++ b/radiomics/glcm.py
@@ -141,19 +141,14 @@ def _calculateMatrix(self, voxelCoordinates=None):
     self.logger.debug('Process calculated matrix')
 
     # Delete rows and columns that specify gray levels not present in the ROI
-    NgVector = range(1, Ng + 1)  # All possible gray values
     GrayLevels = self.coefficients['grayLevels']  # Gray values present in ROI
-    emptyGrayLevels = numpy.array(list(set(NgVector) - set(GrayLevels)), dtype=int)  # Gray values NOT present in ROI
-
-    P_glcm = numpy.delete(P_glcm, emptyGrayLevels - 1, 1)
-    P_glcm = numpy.delete(P_glcm, emptyGrayLevels - 1, 2)
+    P_glcm = P_glcm[:, GrayLevels - 1, :, :]
+    P_glcm = P_glcm[:, :, GrayLevels - 1, :]
 
     # Optionally make GLCMs symmetrical for each angle
     if self.symmetricalGLCM:
       self.logger.debug('Create symmetrical matrix')
-      # Transpose and copy GLCM and add it to P_glcm. Numpy.transpose returns a view if possible, use .copy() to ensure
-      # a copy of the array is used and not just a view (otherwise erroneous additions can occur)
-      P_glcm += numpy.transpose(P_glcm, (0, 2, 1, 3)).copy()
+      P_glcm = P_glcm + numpy.transpose(P_glcm, (0, 2, 1, 3))
 
     # Optionally apply a weighting factor
     if self.weightingNorm is not None: