I'm studying the U-Net CNN architecture. I'm new to CNNs and am confused regarding the "number of channels".
Referring to the U-Net diagram, the input image is convolved with a 3x3 mask which generates a 570x570 output. This output image is then convolved again by a 3x3 mask to produce a 568 x 568 signal. However, what do the 64's correspond to?
The U-net says something about a multi-channel feature map. But how does convolving an image by a 3x3 mask results in a "64".