preprocess_image.py

from skimage.transform import resize

target_size = 96

def preprocess_image(x):
    # Resize the image to have the shape of (96,96)
    x = resize(x, (target_size, target_size),
            mode='constant',
            anti_aliasing=False)
    
    # convert to 3 channel (RGB)
    x = np.stack((x,)*3, axis=-1) 
    
    # Make sure it is a float32, here is why 
    # https://www.quora.com/When-should-I-use-tf-float32-vs-tf-float64-in-TensorFlow
    return x.astype(np.float32)