up6 = merge([Convolution2D(256, 2, 2,activation='relu', border_mode='same')(UpSampling2D(size=(2, 2))(conv5)), conv4], mode='concat', concat_axis=1)

concat_axis=1,why not 0? the input size is [channels height width],so I think axis=1 corresponds to height but not channel. Please tell me why?