Actually, my results are quite nice now, as I have waited a bit longer for training to complete. But on areas with little color variation one can still spot stitches.
Note that the authors say they use 180x180 images but they actually split them into 40x40 pixels patches. Patches that overlap each other every 20 pixels. And they train the network on those patches.
I think that maybe the authors got their final results by not just splitting an input image into separate 40x40 patches, but they also included those overlapping one, and ran all of them through the network. After that they used inferred overlapped patches and separate patches and used some form of interpolation to blend between them. I think that could work but would induce some performance cost to obtaining the final output image. And authors don’t mention anything like that so it’s just my guess.