Is it possible to define unetlayers which considers only one pixel at a time in the input image?

I want to use UNET for my image segmentation but want the Filter size 1*1 of first 2D convolution Layer so that it considers only a single pixel at a time. My image is gray scale. But I dont know how to set parameters of different layers in the bridge and decoder section. I want encoder depth of 1 only. If anyone can help? I m thankful.