diff --git a/pixelocr/page.py b/pixelocr/page.py
index 6064fe1..fbf2cb5 100644
--- a/pixelocr/page.py
+++ b/pixelocr/page.py
@@ -101,9 +101,11 @@ class Line(PageObject):
         """Detect baseline height, relative to the top."""
         bitmap = self.image.bitmap.astype(np.float)
         histogram = bitmap.sum(axis=1)
-        gradient = filters.correlate1d(histogram, [-1, 1], axis=0)
+        gradient = list(filters.correlate1d(histogram, [-1, 1], axis=0, mode='constant'))
+        gradient[0] = histogram[0]
+        gradient.append(-histogram[-1])
         # top = gradient.argmax()
-        bottom = gradient.argmin()
+        bottom = np.argmin(gradient)
         return self.y + bottom
 
     @property