fix image.py

tensorpack/dataflow/image.py

@@ -11,11 +11,12 @@ __all__ = ['ImageFromFile']
 
 class ImageFromFile(DataFlow):
     """ generate rgb images from files """
-    def __init__(self, files, channel, resize=None):
+    def __init__(self, files, channel=3, resize=None):
         """ files: list of file path
             channel: 1 or 3 channel
-            resize: a (w, h) tuple. If given, will force a resize
+            resize: a (h, w) tuple. If given, will force a resize
         """
+        assert len(self.files)
         self.files = files
         self.channel = int(channel)
         self.resize = resize
@@ -30,6 +31,6 @@ class ImageFromFile(DataFlow):
             if self.channel == 3:
                 im = cv2.cvtColor(im, cv2.COLOR_BGR2RGB)
             if self.resize is not None:
-                im = cv2.resize(im, self.resize)
-            yield (im,)
+                im = cv2.resize(im, self.resize[::-1])
+            yield [im]