Add documentation for 'subset' and interpolation' arguments (ImageDataGenerator)
diff --git a/keras/preprocessing/image.py b/keras/preprocessing/image.py
index 901f43ae43d..7013b2a4fdd 100644
--- a/keras/preprocessing/image.py
+++ b/keras/preprocessing/image.py
@@ -680,6 +680,8 @@ def flow(self, x, y=None, batch_size=32, shuffle=True, seed=None,
                save_prefix: str (default: `''`). Prefix to use for filenames of saved pictures
                 (only relevant if `save_to_dir` is set).
                 save_format: one of "png", "jpeg" (only relevant if `save_to_dir` is set). Default: "png".
+               subset: Subset of data (`"training"` or `"validation"`) if
+                `validation_split` is set in `ImageDataGenerator`.
 
         # Returns
             An Iterator yielding tuples of `(x, y)` where `x` is a numpy array of image data and
@@ -739,6 +741,14 @@ def flow_from_directory(self, directory,
                 save_prefix: str. Prefix to use for filenames of saved pictures (only relevant if `save_to_dir` is set).
                 save_format: one of "png", "jpeg" (only relevant if `save_to_dir` is set). Default: "png".
                 follow_links: whether to follow symlinks inside class subdirectories (default: False).
+                subset: Subset of data (`"training"` or `"validation"`) if
+                 `validation_split` is set in `ImageDataGenerator`.
+                interpolation: Interpolation method used to resample the image if the
+                 target size is different from that of the loaded image.
+                 Supported methods are `"nearest"`, `"bilinear"`, and `"bicubic"`.
+                 If PIL version 1.1.3 or newer is installed, `"lanczos"` is also
+                 supported. If PIL version 3.4.0 or newer is installed, `"box"` and
+                 `"hamming"` are also supported. By default, `"nearest"` is used.
 
         # Returns
             A DirectoryIterator yielding tuples of `(x, y)` where `x` is a numpy array of image data and

Methods flow (subset) and flow_from_directory (subset + interpolation) are currently missing it.