Figure 2.

Illustration of U-Net convolution network structure. The left side of the U-shape is the encoding stage, also called contraction path with each layer consisting of two 3 ∗ 3 convolutions with ReLu activation and a 2 ∗ 2 maximum pooling layer. The right side of the U-shape, also called expansion part, consists of the decoding stage and the upsampling process that is realized via 2 ∗ 2 deconvolution to reduce the quantity of input channels by half [2].