diff --git a/derain b/derain
index 280c47a..ce5ff25 100755
--- a/derain
+++ b/derain
@@ -1,6 +1,7 @@
 #!/usr/bin/env python
 
 import argparse
+import img
 from scipy.misc import imread, imsave
 from cv2.ximgproc import guidedFilter
 from guided_filter.core.filters import FastGuidedFilter
@@ -20,11 +21,7 @@ parser.add_argument(
 
 args = parser.parse_args()
 
-img = imread(args.input)
-
-gf = FastGuidedFilter(img,16,2,4)
-img_base = gf.filter(img)
-img_detail = img / 255.0 - img_base
+img_base, img_detail = img.split(imread(args.input))
 
 img_combine = img_base + img_detail
 
diff --git a/img.py b/img.py
new file mode 100644
index 0000000..0440b5e
--- /dev/null
+++ b/img.py
@@ -0,0 +1,7 @@
+from guided_filter.core.filters import FastGuidedFilter
+
+def split(img):
+    gf = FastGuidedFilter(img, 16, 2, 4)
+    base = gf.filter(img)
+    detail = img / 255.0 - base
+    return (base, detail)