Solved by vmirly1 in post #5 
              
              
                Yes, that’s right. I did not notice that the output size should be [2048, 1, 12, 12], so specifically 1 output channel. So the convolution kernel shape is [output_channels, input_channels, kernel_dim_0, kernel_dim_1]. 
So determining the kernel size: 

Desired output channels: 1

Input channels: 1

…