make ImageDataGenerator behaviour fully seedable/repeatable (keras-te…

…am#3751)

* make ImageDataGenerator behaviour fully seedable/repeatable

This makes ImageDataGenerator fully seedable.
- the seed argument in fit is now used
- the seed argument in flow and flow_from_directory now effects
transforms
- added example to docs of transforming images and masks together
- added test of using two seeded streams at once

* implemented requested changes

- PEP8
- explicit names
- classes=None
- remove test

docs/templates/preprocessing/image.md

@@ -56,12 +56,14 @@ Generate batches of tensor image data with real-time data augmentation. The data
             - __X__: sample data.
             - __augment__: Boolean (default: False). Whether to fit on randomly augmented samples.
             - __rounds__: int (default: 1). If augment, how many augmentation passes over the data to use.
+            - __seed__: int (default: None). Random seed.
     - __flow(X, y)__: Takes numpy data & label arrays, and generates batches of augmented/normalized data. Yields batches indefinitely, in an infinite loop.
         - __Arguments__:
             - __X__: data.
             - __y__: labels.
             - __batch_size__: int (default: 32).
             - __shuffle__: boolean (defaut: True).
+            - __seed__: int (default: None).
             - __save_to_dir__: None or str (default: None). This allows you to optimally specify a directory to which to save the augmented pictures being generated (useful for visualizing what you are doing).
             - __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: "jpeg".
@@ -77,7 +79,7 @@ Generate batches of tensor image data with real-time data augmentation. The data
             - __class_mode__: one of "categorical", "binary", "sparse" or None. Default: "categorical". Determines the type of label arrays that are returned: "categorical" will be 2D one-hot encoded labels, "binary" will be 1D binary labels, "sparse" will be 1D integer labels. If None, no labels are returned (the generator will only yield batches of image data, which is useful to use `model.predict_generator()`, `model.evaluate_generator()`, etc.).
             - __batch_size__: size of the batches of data (default: 32).
             - __shuffle__: whether to shuffle the data (default: True)
-            - __seed__: optional random seed for shuffling.
+            - __seed__: optional random seed for shuffling and transformations.
             - __save_to_dir__: None or str (default: None). This allows you to optimally specify a directory to which to save the augmented pictures being generated (useful for visualizing what you are doing).
             - __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: "jpeg".
@@ -151,3 +153,40 @@ model.fit_generator(
         validation_data=validation_generator,
         nb_val_samples=800)
 ```
+
+Example of transforming images and masks together.
+
+```python
+# we create two instances with the same arguments
+data_gen_args = dict(featurewise_center=True,
+                     featurewise_std_normalization=True,
+                     rotation_range=90.,
+                     width_shift_range=0.1,
+                     height_shift_range=0.1,
+                     zoom_range=0.2)
+image_datagen = ImageDataGenerator(**data_gen_args)
+mask_datagen = ImageDataGenerator(**data_gen_args)
+
+# Provide the same seed and keyword arguments to the fit and flow methods
+seed = 1
+image_datagen.fit(images, augment=True, seed=seed)
+mask_datagen.fit(masks, augment=True, seed=seed)
+
+image_generator = image_datagen.flow_from_directory(
+    'data/images',
+    class_mode=None,
+    seed=seed)
+
+mask_generator = mask_datagen.flow_from_directory(
+    'data/masks',
+    class_mode=None,
+    seed=seed)
+
+# combine generators into one which yields image and masks
+train_generator = zip(image_generator, mask_generator)
+
+model.fit_generator(
+    train_generator,
+    samples_per_epoch=2000,
+    nb_epoch=50)
+```

keras/preprocessing/image.py

@@ -390,6 +390,9 @@ def fit(self, X,
                 how many augmentation passes to do over the data
             seed: random seed.
         '''
+        if seed is not None:
+            np.random.seed(seed)
+
         X = np.copy(X)
         if augment:
             aX = np.zeros(tuple([rounds * X.shape[0]] + list(X.shape)[1:]))
@@ -431,11 +434,11 @@ def _flow_index(self, N, batch_size=32, shuffle=False, seed=None):
         # ensure self.batch_index is 0
         self.reset()
         while 1:
+            if seed is not None:
+                np.random.seed(seed + self.total_batches_seen)
             if self.batch_index == 0:
                 index_array = np.arange(N)
                 if shuffle:
-                    if seed is not None:
-                        np.random.seed(seed + self.total_batches_seen)
                     index_array = np.random.permutation(N)
 
             current_index = (self.batch_index * batch_size) % N