about train size

[andre20000131]

hi,
dongyoung,I would like to ask you a question.

i found that you make all images resized to 256×256 images as used in U-Net.i want to know why resized to 256,if i want use 4k(3840,2160) to train unet, Will this have any impact? and , if i train use 256 but when i test image, i use 4k image, Will it affect accuracy?
In short, what is the size of my training that I want to apply to 4k images? I saw that you have a crop operation, and I am very puzzled why do you still need to resize the original image after the crop? I would like to hear your suggestions and look forward to your response.