Fix ImageDataGenerator docs

docs/templates/preprocessing/image.md

@@ -14,7 +14,7 @@ keras.preprocessing.image.ImageDataGenerator(featurewise_center=True,
     vertical_flip=False)
 ```
 
-Generate batches of tensor image data with real-time data augmentation.
+Generate batches of tensor image data with real-time data augmentation. The data will be looped over (in batches) indefinitely.
 
 - __Arguments__:
     - __featurewise_center__: Boolean. Set input mean to 0 over the dataset.
@@ -62,9 +62,19 @@ datagen = ImageDataGenerator(
 # (std, mean, and principal components if ZCA whitening is applied)
 datagen.fit(X_train)
 
+# fits the model on batches with real-time data augmentation:
+model.fit_generator(datagen.flow(X_train, Y_train, batch_size=32),
+                    samples_per_epoch=len(X_train), nb_epoch=nb_epoch)
+
+# here's a more "manual" example
 for e in range(nb_epoch):
     print 'Epoch', e
-    # batch train with realtime data augmentation
-    for X_batch, Y_batch in datagen.flow(X_train, Y_train):
+    batches = 0
+    for X_batch, Y_batch in datagen.flow(X_train, Y_train, batch_size=32):
         loss = model.train(X_batch, Y_batch)
+        batches += 1
+        if batches >= len(X_train) / 32:
+            # we need to break the loop by hand because
+            # the generator loops indefinitely
+            break
 ```