Data augmentation

train_datagen = ImageDataGenerator(
	rotation_range=40,
	width_shift_range=0.2,
	height_shift_range=0.2,
	shear_range=0.2,
	zoom_range=0.2,
	horizontal_flip=True,
	fill_mode='nearest')

• rotation_range is a value in degrees (0–180) within which to randomly rotate pictures.
• width_shift and height_shift are ranges (as a fraction of total width or height) within which to randomly translate pictures vertically or horizontally.
• shear_range is for randomly applying shearing transformations.
• zoom_range is for randomly zooming inside pictures.
• horizontal_flip is for randomly flipping half of the images horizontally. This is relevant when there are no assumptions of horizontal assymmetry (e.g. real-world pictures).
• fill_mode is the strategy used for filling in newly created pixels, which can appear after a rotation or a width/height shift.