Why the output of FCN32 is a black image (zero values)?

[Shima Caffe]

Hi,

I am trying to get the output from FCN 32. I trained FCN32 with pascalcontext-fcn32-heavy.caffemodel pre-trained model. I could run for grayscale images with 5 classes. However, during inference, the output is all zero (a black image). I have two major questions:

1. I am wondering why the output is black? and 
2. How can I know when to stop running the algorithm (i.e., iteration number)? I really do not know what is the optimum iteration number and loss value that I can stop fine tuning in that stage. I stopped training in 40.000 iteration, I have no idea about this.
   

I have attached two files: the log file of the inference and the inference code. 

I really do not know how much I am doing the right way. Quite CONFUSED :(

Does anyone have any suggestion? I really appreciate your help.

Thanks in advance