Make normalization optional

Closes #216 (closed)

dan/ocr/predict/inference.py

@@ -125,6 +125,9 @@ class DAN:
         image = read_image(path)
         preprocessed_image = self.preprocessing_transforms(image)
 
+        if self.mean is None and self.std is None:
+            return preprocessed_image, preprocessed_image
+
         size = preprocessed_image.shape
         normalized_image = torch.zeros(size)