[Solvd]: Output tensors to a Model must be Keras tensors. Found: Tensor

 You can use the Lambda layer to wrap your tensorflow operations

from tensorflow.python.keras.layers import Lambda;def norm(fc2):    fc2_norm = K.l2_normalize(fc2, axis = 3);    illum_est = tf.reduce_sum(fc2_norm, axis = (1, 2));    illum_est = K.l2_normalize(illum_est);    return illum_est;illum_est = Lambda(norm)(fc2);