import tensorflow as tf

                   .FullyConnected('fct', out_dim=6, nl=tf.identity,
                                   W_init=tf.constant_initializer(),
                                   b_init=tf.constant_initializer([1, 0, HALF_DIFF, 0, 1, HALF_DIFF]))())
            # output 6 parameters for affine transformation
            stn = tf.reshape(stn, [-1, 2, 3], name='affine')  # bx2x3
            stn = tf.reshape(tf.transpose(stn, [2, 0, 1]), [3, -1])  # 3 x (bx2)
            coor = tf.reshape(tf.matmul(xys, stn),
                              [WARP_TARGET_SIZE, WARP_TARGET_SIZE, -1, 2])
