EIGHT_UNBALANCE = 37

def weighted_binary_crossentropy(y_true, y_pred):
    # Calculate the binary crossentropy
    b_ce = K.binary_crossentropy(y_true, y_pred)

    # Apply the weights
    weight_vector = (y_true * WEIGHT_UNBALANCE + (1.-y_true)) / 2.
    weighted_b_ce = weight_vector * b_ce

    return K.mean(weighted_b_ce,axis=-1)