Reformat image preprocessing code

[bvarjavand]

Reformat the code in preprocess.py and image_process.py, along with tests in test_preprocess.py and test_image_processs.py. This means:

• [ ] typing hints on every method and class
• [ ] google-formatted docstrings on every method and class
• [ ] input checking (TypeError and ValueError) on every input for every method
• [ ] tests on each method validating inputs
• [ ] tests on each method validating returns
• [ ] docstring on each test describing what it does

An example method which has been refomatted. An example method which has not been reformatted. Note the lack of type hints and type checking. An example which lacks documentation.