Fig. 3.

Network structure of the convolutional neural network (CNN) in our proposed spatially-constrained quantification (SQ) module, i.e., U-Net. The blue blocks represent spatial feature maps obtained from spatial convolutions, and gray blocks represent feature maps copied from previous layers. Each feature map has one feature dimension and two spatial dimensions, while only one feature dimension and one spatial dimension are shown for simplicity. The feature dimension is labeled on the top of each block.