x = (images.reshape(n_images, -1) - np.mean(images)) / np.std(images)
y = bounding_boxes.reshape(n_images, -1) / img_size
x_train, x_test, y_train, y_test = train_test_split(x, y, test_size = 0.33, random_state = 42)
x.shape, y.shape