Error UnicodeDecodeError: 'utf-8' codec can't decode byte 0xff in position 0: invalid start byte

https://github.com/affinelayer/pix2pix-tensorflow/tree/master/tools

An error occurred when compiling "process.py" on the above site.

python tools/process.py --input_dir data --operation resize --output_dir data2/resizedata/0.jpg -> data2/resize/0.pngTraceback (most recent call last):  File "tools/process.py", line 235, in <module>    main()  File "tools/process.py", line 167, in main    src = load(src_path)  File "tools/process.py", line 113, in load    contents = open(path).read()  File"/home/user/anaconda3/envs/tensorflow_2/lib/python3.5/codecs.py", line 321, in decode    (result, consumed) = self._buffer_decode(data, self.errors, final)UnicodeDecodeError: 'utf-8' codec can't decode byte 0xff in position 0: invalid start byte

What is the cause of the error?Python's version is 3.5.2.