Penalize low density regions on an image

Hi thank you for your response. Are you suggesting to use CrossEntropyLoss? My model and training steps are same as in the following link: UNET model on GPU runtime error
The issue is for each image patch that I have a very small portion of it belongs to mask pixel class of 1. My ground truth only has 2-pixel values. Either 1 or zero.

I am not sure how to implement a weighted loss increasing it for the loss class of 0. Can you suggest some methods?